Telemetry User Manual

Contents

Introduction

[20-MAY-25] Our telemetry sensors and stimulators are battery-powered devices designed for use with small animals. All devices capable of transmitting samples or acknowledgements do so using the same frequency-modulated, microwave messages. All devices capable of receiving commands respond to the same amplitude-modulated, microwave commands. Animals can be co-housed or housed separately. Telemetry receivers record signals from all devices within range of their antennas. Command transmitters control all devices within range of their antennas. Combined telemetry receivers and command transmitters use the same antennas to both record and control all devices within range of their antennas.

Figure: Example Subcutaneous Transmitters (SCTs). Left: The two-channel A3049H for adult mice and small rats, 2.9±0.1 g. The A3049H2Z variant has bandwidth 0.0-80 Hz, 120-mV dynamic range, and operating life 40 days. The A3049H4 variant has bandwidth 0.3-320 Hz, 30-mV dynamic range, and operating life 13 days. Right: The single-channel A3048S for adult mice. Mass 1.9±0.1 g. The A3048S2 has bandwidth 0.2-80 Hz, 30-mV dynamic range, and operating life 41 days.

Our Subcutaneous Transmitters (SCT) are small, battery-powered telemetry sensors designed for implantation beneath the skin of mice and rats. Animals with implanted SCTs can be co-housed. We turn them on and off with a magnet. Each SCT measures between one and four biopotentials. Some measure temperature as well. All versions sample biopotentials with an on-board sixteen-bit analog-to-digital converter. Features such as input dynamic range, low-frequency cut-off, bandwidth, sample rate, device mass, operating life, lead length, and lead terminations are chosen by the customer to suit their needs, subject to the constraints of current consumption and battery capacity. Typical dynamic ranges are 30 mV, 120 mV, and 300 mV. The pass-band of a sensor is the range of frequencies it can record faithfully. The passband of our SCTs can occupy any portion of 0.0-640 Hz. One of the most common pass-bands is 0.2-80 Hz. Another popular pass-band is 0.0-160 Hz. Less common is 0.2-640 Hz. Sample rates range from 64-2048 SPS (samples per second). Operating life can be as short as seven days and as long as five years. Our smallest transmitters have mass 1.5 g and are suitable for implantation in young mice. Our largest are 14 g and suitable for implantation in large rats. All our existing SCTs turn on and off with a magnet. Their batteries cannot be replaced, but operating life is often long enough to permit several useful implantations of the same device.

Figure: Four-Channel Head-Mounting Transitter (HMT). An A3040D3Z wrapped in teflon tape. Mass 2.2±0.1 g. The A3040D3Z variant has bandwidth 0.00-160 Hz and operating life 7 days.

Our Head-Mounting Transmitters (HMT) attach to an Electrode Interface Fixture (EIF) cemented to the skull of an animal. They have no on-off switch, but we can remove one HMT and replace it with another with the same signal channel numbers and a fresh battery. We can then replace the battery in the exhausted HMT and prepare it for redeployment later. Although our telemetry system supports recording from multiple HMTs in the same animal cage, we recommend against co-housing animals with HMTs because it is so easy for one animal to chew on the HMT mounted on one of its cage-mates.

Our Implantable Inertial Sensors (IIS) transmit acceleration and rotation. They turn on and off with a magnet. The IIS is designed for implantation in animals or attachment to fish. When implanted in animals, the animals can be co-housed.

Figure: Implantable Stimulator-Transponder (IST). This is the A3041C with an attached test lamp.

Our Implantable Stimulator-Transponders (ISTs) hibernate when placed next to a magnet, but otherwise are activated and controlled by amplitude-modulated microwaves. These amplitude modulated commands are distinct from the frequency-modulated messages transmitted by our implantable devices, but they use of the same telemetry antennas. Animals implanted with ISTs can be co-housed.

Figure: Schematic of Telemetry System. A TCB-B16 telemetry receiver and command transmitter connects to four antennas with coaxial cables that enter a Faraday enclosure by coaxial feedthroughs. A PoE switch provides power and communication. A network cable passes into the Faraday enclosure for a camera.

A Telemetry System at the very least consists of one or more telemetry sensors, a telemetry receiver, and a data acquisition computer running our LWDAQ Software. Most telemetry systems include one or more Faraday enclosures to isolate the system from ambient microwave interference. Some telemetry systems use a combined telemetry receiver and command transmitter in order to operate our implantable stimulators as well as receive from our implantable sensors. The computer and receiver communicate with one another over TCPIP messages. A coaxial antenna receiver gathers telemetry signals with telemetry antennas on the end of coaxial cables. A coil array receiver gathers telemetry signals with antennas fixed in an array on a platform.

Figure: Telemetry Antenna (A3015C). For use with coaxial antenna receivers.

The Animal Location Tracker (A3038, or ALT) is a coil array receiver that we connect to Power over Ethernet (PoE). The Telemetry Control Box (TCB) is a coaxial antenna receiver. The discontinued Octal Data Receiver (ODR) is a coaxial antenna receiver that requires a LWDAQ Driver to provide power and an Ethernet interface.

Figure: Animal Location Tracker (ALT).

The ALT requires no external antennas. It will record from whatever transmitters share its Faraday enclosure, or we can configure the ALT to record from only certain transmitters. The ALT provides, in addition to telemetry signals, a measurement of the position of each transmitter on its array of detector coils.

Figure: Telemetry Control Box (TCB).

The Telemetry Control Box (TCB-A16) provides sixteen antenna inputs to which we can connect up to sixteen Telemetry Antennas (A3015) for telemetry reception. The Telemetry Control Box (TCB-B16) provides sixteen antenna connections that act both as telemetry receivers and command transmitters for radio-controlled implants. We can place four such antennas in each of four bench-top Faraday enclosures. Or we can place sixteen antennas in a single Faraday canopy that encloses a shelf or rack. In each case, we can record from dozens of animals.

Figure: Schematic of Coil Array Telemetry System. We have two Animal Location Trackers in each of Four Faraday Enclosures (FE3A). A data acquisition computer (1) runs the Neurotracker software and records telemetry and position to disk. A power over Ethernet switch (2) provides communication between eight ALTs and the computer, as well as providing power to the ALTs. Unshielded Ethernet cables (4) connect the switch to a feedthrough (8) in the back wall of each Faraday enclosure (5). A shielded Ethernet cable (3) completes the connection to the ALT (6) inside the enclosure. Each ALT will provide tracking for half a dozen animals with implanted transmitters (7).

Our Faraday enclosures isolate the telemetry system from ambient microwave interference. Before investing in one of our telemetry systems, send us your animal laboratory's latitude and longitude so we can check for nearby mobile phone base stations. We will consult a global database to see if there are any base stations near your building. We recommend you do not attempt to operate our telemetry system within 50 m of a 6-kW base station or within 20 m of a 1-kW base station. Our telemetry system uses the 902-928 MHz band for communication. This band is one of the unlicensed Industrial, Scientific, and Medical (ISM) bands in the United States, so we are free to transmit power in this band without a license. But in other countries this same band may be assigned for licensed use, in which case our Faraday enclosures serve two purposes. Not only do they isolate the telemetry system from local, licensed microwave interference, they also prevent the telemetry system from radiating microwave power in any licensed frequency band.

Figure: Subcutaneous Transmitters. D: dual-channel, 6.0 g. S: single-channel, 1.9 g. H: dual-channel, 2.9 g. B: single-channel, 2.2 g.

Our SCT and HMTs will monitor electroencephalogram (EEG), local field potential (LFP), electrocorticogram (ECoG), electrocardiogram (ECG), electromyogram (EMG), and electrogastogram (EGG) at frequencies down to 0.0 Hz and up to 640 Hz. We describe the sources of EEG, LFP, and ECoG in The Sources of EEG. For recordings made with our devices, see our Example Recordings. We currently have three models of SCT in production, each of which is available in a large number of variants. Every operational input on an SCT or HMT produces a stream of telemetry samples with a particular identifying channel number. Thus we refer to a transmitter with two sampled inputs as a two-channel transmitter, and so on.

The A3048 SCTs are a family of single-channel telemetry sensors. The A3048P is our smallest telemetry sensor with mass 1.5 g and thickness 3.7 mm. The A3048S is slightly larger, with mass 1.9 g. The A3048S2, with its 0.2-80 Hz passband and 256 SPS sample rate, is our most popular EEG sensor. The A3049 SCTs are a family of one and two-channel sensors. The smallest A3049 is the A3049W with mass 2.0 g. The largest A3049 is the A3049L with mass 14 g. The A3047 is a one to four-channel SCT that incorporates its own temperature sensor. The mass the A3047A is 6.7 g. The A3040 HMTs are a family one to four-channel head-mounting sensors with mass 2.2 g. All these families of SCTs and HMTs can be configured for both AC and DC recordings.

Figure: Connections for Animal Cage Cameras and an Octal Data Receiver. The Octal Data Receiver is now discontinued, but many remain in service. Shielded Ethernet cables are thick, solid lines. Unshielded Ethernet cables are thick, hollow lines. Coaxial cables for radio frequency signals are thin, solid lines. Two BNC feedthroughs provide connection for coaxial cables running to antennas inside a Faraday enclosure. Two shielded Ethernet feedthroughs provide connection for Ethernet cables running to cameras inside the same enclosure.

The primary purpose of our telemetry system is to record biopotentials continuously for weeks at a time, to provide intermittent stimuli for weeks at a time, and to analyze the recordings automatically. When recording EEG in epileptic animals, we want to count seizures in tens of thousands of hours of recording. Our two-channel transmitters can be equipped with either three or four leads. In the three-lead configuration, the two biopotential inputs share the same reference potential. These devices are ideal for recording EEG in two locations using the cerabellum as the reference potential. In the four-lead configuration, each input has its own reference potential. These devices are ideal for recording two distinct biopotentials, such as EEG and ECG. Our four-channel transmitters can be equipped with eight leads, so that each input has its own reference potential. These devices are ideal for measuring four distinct biopotentials, such as EEG, ECG, EMG, and EGG.

We assemble every set of telemetry sensors to suit each customer's requirements. To record spreading depolarization and all ictal activity with the same input, we set the pass-band to 0.0-160 Hz and the dynamic range to 120 mV. To count epileptic seizures with the greatest accuracy and precision, we set the pass-band to 0.2-80 Hz and the dynamic range to 30 mV. To record EGG we set the pass-band to 0.0-20 Hz. The bandwidth of a sensor is, strictly speaking, the width of the pass-band, but we use "bandwidth" to mean the high-frequency cut-off of the pass-band. Our low-frequency cut-off is always so much smaller than the high-frequency cut-off that the bandwidth and the high-frequency cut-off are almost the same. The higher the bandwidth of an input, the higher the sample rate we must use to record the signal, and the higher the current consumption of the device. Operating life of SCTs and HMTs is inversely proportional the current consumption, as we discuss below. The larger the dynamic range, the greater the electronic and quantization noise in the recorded signal. The greater the mass of the device, the larger the battery, and therefore the longer the operating life.

You will find the prices of subcutaneous transmitter system components in our price list. Our Event Detection page gives a history of our automatic event detection software. You will discussion of the technology behind our telemetry system in the Appendices.

Components

[06-MAY-25] Our transmitters provide one or more telemetry signals, depending upon how they are configured. We have two classes of telemetry receiver: coaxial antenna and coil array. The coaxial antenna systems use antennas on the end of coaxial cables. We distribute the antennas among our Faraday enclosures, placing them between and adjacent to our animal cages. A coaxial antenna system will record from a hundred transmitters. Our Telemetry Control Box (TCB) is a coaxial antenna system. It provides an approximate animal location measurement for multi-room habitats, by reporting which of its antennas is receiving the most power from each telemetry channel. Our coil array systems provide a platform upon which we can place one or two animal cages. Beneath the platform is an array of antenna coils. The array provides activity measurement in units of centimeters moved per unit time, and reliable disambiguation of animals in video recordings. Our Animal Location Tracker (ALT) is a coil array.

The Telemetry Control Box (A3042, TCB-A16, TCB-B16) and Animal Location Tracker (A3038, ALT) require only one Power over Ethernet (PoE) connection for power and communication combined. The TCB-A16 provides sixteen antenna inputs, each with its own independent telemetry receiver. The TCB-B16 provides the same sixteen antennas, but each can be used to receive telemetry or transmit commands to radio-controlled devices such as the Imlantable Stimulator-Transponder (A3041). The ALT permits recording from all animals moving over its coil array. The A3038C platform is 51 cm × 27 cm, so we can place one large rat cage or two small mouse cages upon a single platform.

Our Octal Data Receiver (A3027, ODR) is now discontinued, but many remain in operation, and we have no plans to discontinue support for them. They operate with a LWDAQ Driver. The ODR comes in a 30 cm × 22 cm × 11 cm metal box. The box connects to the LWDAQ Driver with a shielded network cable. It receives power through the same cable. Eight BNC sockets on the back of the box provide connections for a coaxial cables to the antennas. There are thirty indicator lights on the front of the box. There is one white light for each transmitter channel, one white light for each antenna input, and power, reset, upload, and empty lights. The Octal Data Receiver comes with eight Dampled Loop Antenna (A3015C). These attach to the antenna inputs with coaxial cables that pass through a Faraday enclosure wall with the help of a BNC feedthrough. Each antenna can stand on its own, or we can take the mounting brackets off and lay it on a table or wedge it between the cages in an IVC rack.

Figure: The Octal Data Receiver and LWDAQ Driver System. We shipped these systems from 2013 to 2023. They have now been replaced by the ALT and TCB, but we will support them indefinitely. The Faraday enclosure is one made by the machine shop at our customer's institute.

Here is a list of electronic assemblies, including sensors and radio-controlled implants.

Faraday enclosures can be bench-top with hinged doors, or they can be canopies supported by an aluminum frame around a free-standing rack of shelves. The bench-top enclosures have back walls made of aluminum sheet where we place coaxial and Ethernet feedthroughs to carray coaxial and Ethernet connections. The canopies have floors made of aluminum sheet to which we attach coaxial and Ethernet feedthroughs.

Set-Up

[15-MAY-25] Before investing in one of our telemetry systems, we suggest you send us your animal laboratory's latitude and longitude so we can consult the global mobile phone base station database for transmitters near your facility. Mobile phone networks that use the 902-928 MHz band are less common now than they were ten years ago, but they still exist. If you have one on the building opposite you, directing power right through your windows, your telemetry system will not perform well.

We recommend you set up your telemetry system several weeks before you plan to perform your first animal experiments. During these weeks, you can install our software on your computer and learn how to acquire and analyze telemetry signals. We supply one or two sample transmitters with your recording system, so use these to test reception and recording. Place one or two transmitters within a Faraday enclosure and record their signals continuously for a week to make sure that your computer, local area network, and hardware is functioning correctly. Recording might be interrupted every few hours, and you will be glad to figure out what causes these interruptions before you have animals with transmitters implanted. Reception from the transmitters may cease all-together every few hours, and you will be glad to figure out what is interfering with reception long before you have begun an experiment with live animals.

List of parts required for a coaxial antenna system with Telemetry Control Box:

1. Power over Ethernet (PoE) Switch (such as PoE-16)
2. Two Short Shielded Ethernet Cables
3. Telemetry Control Box (TCB)
4. Either a Faraday Enclosure (FE3B) or a Faraday Canopy (FE5A) with 8-8 Coaxial Feedthrough (A3039E)
5. Subcutaneous Transmitter (such as the A3049)
6. A Magnet (such as a cow magnet)

List of parts required for a coil array recording system with Animal Location Tracker:

1. Power over Ethernet (PoE) Switch (such as PoE-16)
2. Long Unshielded Ethernet Cable
3. Short Shielded Ethernet Cable
4. One or more Animal Location Trackers (A3038)
5. Faraday Enclosure (FE3A) or Faraday Canopy (FE5A) with 8-8 Ethernet Feedthrough (A3039D)
6. Subcutaneous Transmitter (such as the A3049)
7. A Magnet (such as a cow magnet)

List of parts required for a coaxial antenna recording system with Octal Data Receiver:

1. Computer Power Cable with Local Wall Plug (use one left over from an old computer)
2. Power Supply (connect to wall power socket)
3. Ethernet Cable (can be shielded or unshielded)
4. LWDAQ Driver (A2071E), the Black Box
5. Shielded LWDAQ Cable (do not use an unshielded Ethernet cable)
6. Octal Data Receiver (A3027), the Silver Box
7. Long Coaxial Cable (with BNC plugs, usually 240 m)
8. Short Coaxial Cable (with BNC plugs, usually 30 cm)
9. Either a Faraday Enclosure (FE3A) or a Faraday Canopy (FE5A) with 8-4 Coaxial Feedthrough (A3039C)
10. Damped Loop Antenna (A3015C)
11. Subcutaneous Transmitter (such as the A3049)
12. A Magnet (such as a cow magnet)

Assuming you have the above parts in hand, follow the set-up steps in the following paragraphs. These steps will take you through the organisation and configuration of your hardware and software. They show you how to test that your system is working well. By the end, you will be able to record from any of our telemetry sensors.

Connect Power: We don't provide the power cord that runs from your wall socket to the plug in our power adaptors. We leave it to you to dig out an old computer power cord for use with the power adaptor. Your power cord will be compatible with your own native wall socket. If your recording system uses Animal Location Trackers (ALTs) or Telemetry Control Boxes (TCBs), plug power into the adaptor that comes with your Power over Ethernet (PoE) switch and plug this adaptor into the switch itself. Place ALTs in Faraday Enclosures. Connect each ALT to the back wall of your enclosure with a shielded network cable. From the back wall connect each to your PoE switch using another network cable, which can be shielded or unshielded. Place TCB near PoE switch and connect with a shielded network cable. If your recording system uses an Octal Data Receiver (ODR) with LWDAQ Driver, plug power into the adaptor that comes with the LWDAQ Driver, and plug this adaptor into the driver itself. Now connect your ODR to one of the sockets on the front side of the driver with a shielded network cable. Do not place your LWDAQ Driver or your PoE switch in your Faraday enclosure. The only things you should permit in your Faraday enclosure are coaxial antennas, ALTs, and video cameras that we have approved for use with our telemetry system.

Connect Recording System to Laptop: If your recording system uses PoE, connect your computer to the same PoE switch with an Ethernet cable. If your recording system uses a LWDAQ Driver, plug an Ethernet cable into the Ethernet socket on the LWDAQ Driver. We ship our LWDAQ Drivers with short, unshielded Ethernet jumper cables for this purpose. The Ethernet socket is the one on the back, next to the power jack. The driver has other sockets of the same type as the Ethernet socket, but these are not Ethernet sockets. They are LWDAQ driver sockets. You can plug your Ethernet cable into them if you like, but it won't do you much good. On the other hand, you won't break anything either. Plug the other end of your Ethernet cable directly into your laptop computer. Download the LWDAQ Software suitable for your computer's operating system from the LWDAQ software download page. Go to our Software Installation section and follow the instructions for your operating system. Go to our Configurator section and follow the instructions to establish communication between your computer and the drivers or PoE receivers. You will set up your computer to operate on a local network that contains only the computer and the recording system. We have done this a bunch of times, so it takes us less than a minute. But the first time you try it can be frustrating.

Connect Recording System to Local Area Network (Optional): Once you have established communication between your computer and recording system, you may wish to configure the recording system to operate on your local area network (LAN). Follow the instructions in the Configurator section of the manual. You may find this step takes a while to accomplish because you will have to work with your network administrator to obtain an Internet address, and they may not be happy about allowing you to put a strange device like a LWDAQ Driver or Animal Location Tracker on their network. You must obtain permission from them to allow connections on port TCPIP protocol port number ninety (90).

Systems with LWDAQ Drivers Only, Test Control of LWDAQ Power Supplies: If your receiver uses a LWDAQ Driver, you can test communication between your computer and the LWDAQ Driver at any time with the Diagnostic Instrument. Try turning on and off the LWDAQ power supplies and obtaining plots of the power supply voltages. When you turn off the power supplies, you will see the three power supply lights turn off.

Systems with LWDAQ Drivers Only, Connect the Receiver: Connect your receiver (such as the Octal Data Receiver, A3027) to your LWDAQ Driver (A2071E or A2037E) with a shielded LWDAQ Cable. We ship the receivers with a shielded cable for this purpose. The shielded cable protects data acquisition from static discharge. Pick one of the LWDAQ sockets on the driver for the connection. Any one will do. Socket number one is the one closest to the indicator lamps. Socket number eight is the one farthest from the indicator lamps. Let's suppose you pick socket number one. You should see a power light come on the receiver. If not, press the hardware reset button on your LWDAQ Driver to bring up the power supplies again. The hardware reset button is next to the indicator lights on the LWDAQ Driver.

Check Receiver: Open the Neurorecorder in the Tool Menu. Specify the assembly number and internet protocol (IP) address of your receiver. If you are using a LWDAQ Driver, specify the socket into which you have plugged your ODR. Select a directory into which you can record an archive file. Press Reset. You should see the red EMPTY light on the receiver flash briefly. Now press Record. You should see the red EMPTY light flashing. Press Signals and you will see a new window open up showing telemetry signals and a clock signal. This new window is the Receiver Instrument.

Coaxial Antenna Systems Only, Connect One Antenna: Connect a long coaxial cable to one of the antenna sockets on the receiver. Whenever you connect a BNC plug to a BNC socket, make sure that you turn the locking flange on the plug until it locks. If you don't lock the connector, your system will still work, but it will work poorly now and then, which makes for a difficult problem to diagnose. Plug the other end of your long coaxial cable into a coaxial feedthrough at the back of your Faraday enclosure or on the floor of your Faraday canopy. Connect another cable inside the Faraday enclosure or canopy from the feedthrough to a Telemetry Antenna (A3015).

Turn On Transmitter: We provide two or more SCTs with each recording system so as to help with your setup. Take one of these and place it near your coaxial antenna or upon a coil array platform. If it's off, bring your magnet next to the transmitter and move it away again. One of the white channel activity lights on receiver should turn on, and at least one of the antenna activity lights as well. If not, try again with the magnet. The transmitter should turn on and off easily. If not, your magnet is not powerful enough or it is too small. The magnets we provide are big and strong. Hold the transmitter in your hand and move it around near the antenna. You should see the Channel Receive light turning off now and then, or it may be intermittent. If you move far enough from the antenna, the light will certainly turn off. The light indicates signal reception. When reception is robust, the intensity of the Channel Receive light is constant.

View Transmitter Signal: You should now see the telemetry signal in the Receiver Instrument. If you are sitting in a Faraday canopy, you may have to look at your computer screen through the steel mesh walls of the canopy. Wet your finges and press the transmitter leads together. You will see noise. The noise on an SCT input is around 20 counts. Other versions may have more or less noise. Separate the leads. You should see mains hum (50 Hz or 60 Hz). Wet the thumb and forefinger of both your hands and hold the tip of each lead in one hand. Rest the transmitter on your bench with the two leads running close together. Try to stay still. You should see a small bump in the received signal every second or so. This bump is your heartbeat.

Test Reception: Place the transmitter near the antenna or coil array. In the Receiver Instrument, you will see a status line below the signal display. This line tells you how many messages are being received from each active channel during each recording interval. By default, the recording interval is 1 s, so you will get 128 clock messages from channel zero. With an active A3049E, you should see 512 messages per second from the transmitter. Watch the reception for a few minutes. When the Channel Receive light starts blinking, the number of messages received will drop in the Receiver Instrument. Does it vary dramatically? If reception is, for example, 100% for three seconds, and 30% for ten seconds, you have local interference power turning off for three seconds, and on for ten seconds.

Coaxial Antenna Systems Only, Connect Additional Antennas: The Octal Data Receiver (A3027) has eight independent antenna inputs, and you can connect two antennas to each of these inputs with the help of BNC T-adaptors or our 8-4 Coaxial Feedthrough (A3039C). Make sure antennas are separated by 30 cm and are at least 5 cm from the conducting walls of the enclosure. For an example of three antennas arranged adequately, see here. We recommend four antennas per Faraday enclosure, with none of the antennas in a single Faraday enclosure being combined with any other antenna in the same enclosure. We recommend eight or sixteen antennas per Faraday canopy, with no antenna combined with any other antenna less than 60 cm distant. Test reception in your enclosures or canopy as described above. If you get less than 95% reception anywhere in the enclosure, with the transmitter on a plastic cup, there is a problem with the system that needs to be fixed.

Record to Disk: Select the Neurorecorder from the Tool menu. Follow the set-up instructions in the Neurorecorder Manual. Press Start to begin recording to disk. Press Receiver to see the raw signals the Neurorecorder is downloading from the receiver.

Exercise the Neuroplayer: Select the Neuroplayer from the Tool menu. The Neuroplayer allows you to play back signals you have recorded to disk, process those signals into summary measurements, and navigate through data archives to examine recorded signals. All these actions are explained in the Neuroplayer Manual. Select your live recording archive and press Play. Experiment with the frequency and voltage displays in the Neuroplayer.

Test Continuous Data-Taking: Consult the Interval Processing section of the Neuroplayer Manual. Create a text file on your computer that contains processing instructions to record reception and power in a few frequency bands. Select this processor in the Neuroplayer and enable processing. With one or more transmitters in your Faraday enclosure, record their signals for several days. Process and display the data as it is being recorded. The data acquisition should proceed without interruption.

Measure Reception: Consult the Interval Analysis section of the Neuroplayer Manual. Download the Reception Average script and paste it into the LWDAQ Toolmaker. Select the channel numbers of your active transmitters. Set the averaging period to an hour. Press Execute to Apply the analysis to all the characteristics files you recorded in the previous few days. You will get the average reception hourly for several days. Plot a graph of reception in Excel or whatever program you like. You should see at least 95% reception on average, more likely 98%. Use the Reception Failure script to look for periods of <80% reception. How often do these occur? Such reception failures are the result of interference penetrating into the system through power supplies and network cables. Save the list of failures in a text file. Select this file as the Events file in the Neuroplayer and use the event navigation buttons to view the failures in detail. You may see hundreds of spurious messages from non-existent channels during the failures.

When our telemetry system consists of several receivers, we will need one Neurorecorder for each. If we want to process the signals as they are recorded, we will need at least one Neuroplayer per receiver. We may even need one Neuroplayer per animal. For example, we may have two animal location trackers (ALTs) with four animals over each tracker, and we want to export the signals from each animal to separate EDF files. We need two Neurorecorders and eight Neuroplayers. The Startup Manager allows us to define our telemetry recording and processing with a script and start all processes by running the script. After an interruption, we can re-start the system with a few mouse clicks.

Operating Range

[06-MAY-25] Reception of our telemetry signals is always limited by RF interference. Our faraday enclosures reduce ambient interference by a factor of one thousand. Where a single antenna receives the signal from an implanted transmitter 95% of the time, two independent antennas pick up the signal 99.5% of the time. Our Telemetry Control Box (TCB-A16) provides sixteen independent antenna inputs. Each input has its own amplifier, demodulator, and decoder. By distributing these antennas between our animal cages, the probability that at least one of them will receive any particular message approaches 100%. With eight antennas distributed through an IVC rack, for example, we obtained 100% reception everywhere within the rack, despite the presence of a 900-MHz mobile phone base station 80 m from the recording room. One TCB-A16 can record from dozens of animals in one such IVC rack. Our FE3A enclosure stands on its own, and is 90 cm wide, 60 cm high, and 65 cm deep. With a shelf half-way up, it holds six animal cages. With four antennas inside, it provides recording from forty co-habiting animals.

We define operating range as the greatest range from the pick-up antenna at which we obtain robust reception. An A3049B3 SCT transmits 512 messages per second, so the operating range is the greatest range at which we receive 410 or more messages per second in 95% of orientations and positions at the operating range. In practice, we operate the transmitters inside a Faraday enclosure, so their operating range must be adequate to cover the range from the antenna in the center of the enclosure to the farthest corner of the enclosure volume. For details of our studies of poor reception in various locations, see our Reception page.

Operating range without a Faraday enclosure varies dramatically with location. In Harwell, UK, in a rural location, we obtained robust reception out in the open at up to 200 cm. In a basement laboratory in Boston, operating range in the open was 150 cm. In a second-floor office in Waltham, MA, operating rante was 70 cm. In the tenth-floor animal room at ION in London, operating range with no enclosure is 20 cm. Decreasing operating range is the result of ambient interference. If you are operating in a basement or in a windowless, central room of a brick building, we suggest you first purchase a hand-held microwave spectrometer and measure your background interference. With this measurement, we can advise you on whether or not you need to include Faraday enclosures in your system.

In all other locations, we recommend you operate in Faraday enclosures, even though they are expensive and add a complication to your study. If your location is not protected by several meters of earth or brick, anyone can put a stop to your study at any time by starting up a 900-MHz GSM base station within a hundred meters of your location. So it's not worth taking the risk just to avoid the expense and inconvenience of the enclosures. We call them Faraday enclosures so we don't get them confused with animal cages, which are used to contain animals. Usually, these conducting cages are called Faraday cages. Our Faraday enclosures are all equipped with microwave absorbers inside, without which they do not function well at all. We describe the performance and construction of Faraday enclosures in Faraday Enclosures. Because Faraday enclosures give us at least a 20-dB (one hundred-fold) reduction in ambient interference, they increase the operating range of our transmitters by a factor of 10 (square root of one thousand). Even if the operating range is only 20 cm without a Faraday enclosure, it will be 200 cm within a Faraday enclosure.

Cleaning and Storage

[12-MAY-25] Let us begin with disinfection, cleaning, and storage of implantable devices, such as our Subcutaneous Transmitters (SCT), Implantable Inertial Sensors (IIS), and Implantable Stimulator-Transponders (IST). All these devices are coated with silicone so that they may be implanted within the body of an animal host. The first time you deploy a particular device, you remove it from the bag or package in which we shipped it to you, disinfect the device, and implant it. Later, when your work with the host animal is complete, you will remove the device from the host. We call this removal explantation. If the device still has sufficient operating life remaining for a second experiment, you must first remove cement from the device's electrodes, cut away remaining scar tissue from around the leads, and wash off the hair and blood that adheres to the device's silicone coating. We call this process cleaning. The final stage of cleaning is to rinse the device in water and dry it off. Now you put it back in the package we provided, make sure it is turned off, and put it on a shelf. We call this process storage. We discuss disinfection, cleaning, and storage of implantable devices in separate paragraphs below. Our objective is to make sure your disinfection, cleaning, and storage are effective, but at the same time avoid causing damage to the implant or exhausting its battery.

Some of our customers use the word sterilization in place of "disinfection". So far as we know, they mean the same thing. We recommend four different ways to disinfect your implantable devices. Feel free to use all four of them, one after the other, if you want to make absolutely sure your devices are sterile. You may disinfect your implantable devices by immersing them in ethanol. Use 70% or 100% ethanol at room temperature. Stir or shake, and allow to sit for for ten minutes. Do not allow them to sit in ethanol for more than one hour. Ethanol dissolves slowly in silicone at room temperature, but not to any significant extent during the course of one hour. You may also disinfect our implantable devices with ethylene oxide gas sterilization. The sterilizing gas process subjects the device to 60°C and 80% humidity for six hours. It causes no harm to the implant's battery and there is insufficient time for the water vapor to penetrate the implant's encapsulation. You may disinfect implantable devices with boiling water. Drop them in the boiling water for up to ten minutes, but no longer. Ten minutes is not long enough for corrosion to initiate in the transmitter encapsulation, but our calculations suggest that an hour will put the transmitter at risk. You may disinfect your implantable devices in an autoclave, provided you limit the temperature and duration of the autoclave process. Autoclave at 121°C and atmospheric pressure for no more than thirty minutes. Autoclave at 132°C and atmospheric pressure for no more than fifteen minutes.

When you clean a transmitter, you will most likely have to immerse it in acetic acid, acetone, or ethanol, or all three. Our devices are encapsulated in epoxy and coated with silicone. Acetic acid does not react with silicone or epoxy any more than does water. Acetic acid dissolves cured cyanoacrylate, so it can be useful for cleaning off cyanoacrylate used to fix electrodes in place during implantation. Feel free to soak our implants in acetic acid at room temperature for one or two days. Acetone dissolves dental cement and cyanoacrylate, so it will dissolve and remove the cement you use to construct head fixtures. Place your device with detnal cement in acetone in a sealed jar at room temperature for six hours. Shake occasionally. Dispose of the dirty acetone. Rince the implant twice in clean acetone. Rinse in water and dry off. By this point, the device should be clean. Do not leave your implant soaking in acetone for more than six hours. Acetone dissolves in silicone and reacts with epoxy, so prolonged exposure to acetone will damage the encapsulation. See Silicone and Solvents for further discussion of acetone as a cleaning fluid. Ethanol dissolves slowly with silicone and epoxy at room temperature. Do not soak your implants in ethanol for more than a few hours. The silicone will begin to take on a slimy feel, and ultimately it will swell and crack. But do feel free to put your implants in a jar of ethanol, shake them for a few minutes, and let them sit for an hour. Exposure to ethanol at room temperature for one hour will not damage the implant.

When you store an implant, we recommend you store it in a dry place at room temperature. Do not store it in any kind of fluid, not even water, and certainly not acetone or ethanol. Assuming the device is dry, it will tolerate storage at any temperature −20°C to 60°C. Provided relative humidity is less than 80%, corrosion within the implant circuit will be slowed to a standstill. The more difficult component to proper storage is making sure the device stays off. Most of our implantable devices turn on with a magnet. Touch them with a magnet and they turn on. Touch them again and they turn off. When we store these, we must first make sure they are turned off, and then store them on a shelf far from any source of magnetic fields. The rest of our devices hibernate when they are placed on a magnet. When we store these, we must make sure they stay sitting on the magnet in the storage box we used to ship them to you. Store all implants at least 30 cm from any electrical power supplies, magnets, or large lumps of iron.

Our Head-Mounting Transmitters (HMT) are not implantable. Nor are they coated in silicone. The HMT is a bare circuit board into which you load a battery, fold up, wrap with teflon tape, and attach to the head of a host animal. It is never implanted. It does not have to operate while immersed in warm saline. Because the HMT is a bare circuit board, however, it is vulnerable to electrostatic discharge. Whenever you carry an HMT, carry it in the anti-static bag in which we shipped it to you. Do not carry an HMT in your bare hands while wearing rubber shoes. While sitting and handling the HMT out of its bag, cover static-generating clothes with a laboratory coat. You may disinfect your HMT using any of the processes we recommend for implantable devices in the preceeding paragraphs. When you detatch an HMT from a host animal, you unwrap its tape and remove the battery. Clean the HMT by washing it in warm running water and scrubbing gently with a toothbrush. After cleaning, dry with compressed air or dab with lint-free cloth and allow to dry in ambient air for twenty-four hours. Now store the HMT in its anti-static bag.

Analog Inputs

[24-OCT-24] Our existing telemetry sensors provided between one and four biopotential inputs. These might share a common reference potential, as in the two-channel A3049H2, or they might each have their own reference potentials, as in the four-channel A3047A3D-C. The figure below is an example of the frequency response we obtain during final quality control of a batch of transmitters before shipping.

Figure: Frequency Response of a Batch of A3049H2 SCTs. The A3049H2 is a two-channel transmitter. Both channels are sampled and transmitted at 256 SPS. The first channel has bandwidth 0.24-80 Hz, the second has bandwidth 0.16-80 Hz.

In our telemetry sensor version tables, we describe each input by its sample rate, high-pass filter frequency, low-pass filter frequency, and input dynamic range. If the amplifier has no high-pass filter, we call it a "DC Transmitter". Otherwise we call it an "AC Transmitter". The dynamic range of the AC transmitters is typically 30 mV, arranged as −18 mV to +12 mV. The dynamic range of DC transmitters is typically 120 mV, arranged as −72 mV to +48 mV. The larger dynamic range allows the DC input to accommodate the largest possible galvanic potential generated by its electrodes. All biopotentials are digitized to sixteen-bit precision before transmission. The raw telemetry signals we read from an NDF file are all sixteen-bit numbers. The value 0 cnt (zer counts) represents the bottom of the dynamic range. The number 65565 cnt represents the top of the dynamic range. We obtain the conversion factor from counts to voltage by dividing the dynamic range by 65536. For input with range 30 mV we use 0.46 μV/cnt, and for an input with range 120 mV we use 1.8 μV/cnt.

Figure: Frequency Response of a Batch of A3049H3Z SCTs. The A3049H3Z is a "DC Transmitter" in that it is sensitive down to 0.0 Hz. It provides two channels with bandwidth 0.0-160 Hz, each sampled at 512 SPS. It is designed to observe spreading depolarization, spreading depression, and ictal activity simultaneously.

When we drop a transmitter in water, we see the electronic noise generated by the transmitter circuit added to the chemical noise generated by the electrodes as they react with the water. With only stainless steel wire for the electrodes, this chemical noise is negligible. For our standard amplifier with gain ×100 and input impedance 10 MΩ, electrical noise is around 5 μV rms in 1-160 Hz, referred to the analog input. With gain ×10 the electrical noise increases to around 10 μV rms in 1-160 Hz.

Figure: Spectrum of Electrical Noise Generated by Channel X4 in A3047A3D. These channels are 0.0-160 Hz, 120 mV range. We take the spectrum of a 32-s interval and plot in the Neuroplayer. Total noise is 5 μV rms.

The distortion of a signal by our telemetry system is the extent to which it changes the shape of a signal. We apply a 10 mVpp sinusoid to the X and Y inputs of an A3049AV3. The AV3 is equipped with two 160-Hz amplifiers. Input dynamic range is 30 mV. We increase the frequency from 1/8 Hz to 200 Hz. For each frequency, we obtain the spectrum of the signal and measure the power outside the sinusoidal frequency as a fraction of the sinusoidal power using this script. We express the result in parts per million.

Figure: Distortion of 10-mVpp Sinusoid versus Sinusoidal Frequency. Non-sinusoidal power as a fraction of sinusoidal power in parts per million. Sine wave generated by BK Precision 4053B, specified total harmonic distortion <1 ppm.

The distortion of the X is dominated by random electronic noise. There are no significant peaks in the spectrum outside the fundamenta.

Figure: Spectrum with 50-Hz, 10-mVpp Sinusoid. Horizonal: 10 Hz/div. Vertical: 0.4 μV/div. The peak is 4000 μV.

Note that the distortion generated by the new A3047, A3048, and A3049 transmitters is hundreds of time less powerful than that of their predecessors (A3013, A3019, and A3028). The new transmitters sample their signals uniformly, thus eliminating the scatter noise present in earlier devices.

Activity Monitoring

[09-FEB-24] Our telemetry system supports four types of activity monitoring. None of the measurements are perfect, but all are useful. The four types are: location monitoring, location tracking, acceleration recording, and acceleration with rotation recording. The first two are provided by the telemetry receiver. The second two are provided by a dedicated implant that holds an accelerometer and gyroscope: the Implantable Inertial Sensor (IIS).

The Telemetry Control Box (TCB) measures the radio-frequency power received by each its antennas whenever it receives and decodes a telemetry message. It provides to us the number of the antenna that received the greatest power and a logarithmic measurement of that power. We call these the top antenna and the top power. In a telemetry system in which the antennas are separated by at least thirty centimeters, the top antenna is almost certainly the one closest to the transmitter. Thus the TCB allows us to determine the location of an animal in a maze or some other environment with multiple chambers. We call this location monitoring.

The Animal Location Tracker (ALT) measures the radio-frequency power received by each of its detector coils whenever it receives and decodes a telemetry message. It provides us with a logarithmic measurement of this power at each of its coils. By taking a weighted centroid of the receive power, the ALT provides us with a location. This location is not an accurate measurement of the location of an animal, but its movement is well-correlated with the movement of the animal, and its value is well-correlated with position. We can use the centroid to obtain a measurement of total distance traveled by each animal in a cage. We can measure the time pairs of animals spend close together. We can use the movement of the centroid to determine which animal is which in continuous video recordings. We call this location tracking.

Both location monitoring and location tracking come at no cost in operating life of the transmitter. We can perform both measurments with any telemetry device that transmits telemetry messages. If we want a higher-resolution measurement of the acceleration of an animal, we must implant an accelerometer. We will obtain 64 SPS of acceleration measurements in three orthogonal directions. We call this measurement acceleration recording. The accelerometer-only versions of the IIS provide acceleration recording. If we want to measure acceleration and rotation, the accelerometer with gyroscope versions of the IIS provide acceleration with gyroscope recording. The gyroscope is power-hungry, so the IIS with gyroscope supports intermittent measurements over a long period, but not continuous measurements.

Example Recordings

[30-NOV-21] We have a library of example telemetry recordings available on our Example Recordings page. You will also find two short example recordings in the LWDAQ/Images folder: they are the two files with extension "ndf".

Figure: The Neuroplayer Demonstration Video. Presents the M1628000358.zip example recording, which contains synchronous EEG and video and illustrates optogenetic stimulus of the brain.

For a tutorial on browsing recordings with the Neuroplayer, see our Neuroplayer Introduction video.

File Format

[12-JUL-23] Our telemetry system records its telemetry signals to disk in files that confrom to our Neuroscience Data Format (NDF). An NDF file begins with the characters " ndf" followed by a four-byte metadata string address, a four-byte data address, and a four-byte metadata string length. The byte ordering is big-endian (most significant byte first). The telemetry data is in the data section, with one record saved per unique message received from the telemetry system. We describe the message format in detail elsewhere, but we will summarize the format here. Each message consists of a core and a payload. The core is four bytes long. The first byte is the telemetry channel identifier. The next two bytes are the message data value, which almost always be a sixteen-bit sample value with its most significant byte first. The fourth byte of the core is a timestamp. The payload consists of further bytes of information obtained from the telemetry receiver. Some receivers produce no payload. Others produce payloads up to sixteen bytes long.

The program that does the recording is the Neurorecorder, which is a tool build into our LWDAQ software. The Neurorecorder writes "payload" field to the NDF metadata string, in which it notes the length of the message payload in the NDF file's messages. The Neurorecorder knows the payload length because it queries the receiver to determine the receiver version, and from this version number the Neurorecorder deduces the message payload length. Here is an example metadata string from an NDF recorded from an Animal Location Tracker (ALT).

Figure: NDF Metadata String, As Displayed by Neuroplayewr.

When we play an NDF recording in the Neuroplayer, the Neuroplayer reads the payload length from the metadata and acts accordingly. The payload provided by an ALT contains the power of the message at each of the ALTs location and auxilliary detectors. The power bytes, combined with the spatial distribution of the ALT's detector coils, allows us to deduce the approximate location, and measure the activity of animals. The "alt" field in the metadata gives the locations of the detector coils in a three-dimensional coordinate system. The payload provided by the TCB gives us the maximum power with which the message was received by any of the TCB's detector coils, and the identifier of that detector coil. The "alt" field for a TCB recording would likewise provide us with the locations of the detector coils, and the top antenna will give us an idea of where the animal is in a large space, or a multi-room habitat, in which we have one or two antennas in each room.

Leads

[29-NOV-23] Our electrode leads are a flexible helix of stainless steel wire insulated in silicone. The outer coat is clear MED-6607, unrestricted medical-grade silicone. The inner layer is SS-5001 with a dye that gives the lead its color. Lead colors we use with our SCTs are: blue, red, orange, purple, yellow, green, pink, and brown. The outer layer has no dye, but consists only of the medical grade silicone.

We can manufacture B-Leads up to 280 mm long and C-Leads up to 130 mm. The 0.5-mm diameter C-Leads leads are far more flexible than the 0.7-mm B-Leads leads. They are less likely to cause irritation and infection in the subject animal. But the spring in the C-Lead is delicate. Its wire is half the diameter of the wire in the B-Lead. The spring itself is one quarter as strong. They will survive the fatigue of animal movement, but they are easy to damage with a scalpel during implantation or extraction. Removing insulation from a 0.5-mm lead is a delicate operation. Furthermore, we cannot provide screw or pin terminations on 0.5-mm leads because the wire breaks so easily at the edge of the solder joint. We can, however, solder the 0.5-mm leads to X-Electrodes directly and insulate with silicone afterwards, which is how we make the EIF-XAAX electrode interface.

The D-Lead we can manufacture up to 130 mm long. It is for use with Implantable Light-Emitting Diodes (ILEDs) in rats. It's wire is thicker and its spring pitch is greater than the B-Lead, which results in its resistance being one quarter that of the B-Lead. The D-Lead is stiffer, but makes it possible to deliver ten milliamps to an ILET that is 100 mm away from our stimulator without wasting half our battery power in lead resistance heating.

For more information on our subcutaneous leads, as well as instructions on stripping and tinning the leads, see our Flexible Wires manual.

Electrodes

[27-NOV-23] We provide a variety of terminations for our electrode leads, and a variety of depth electrodes to which these terminations can be connected. See Electrodes and Terminations for a list of terminations and depth electrodes with links to photographs and drawings.

Antennas

[18-MAY-25] The table below lists the various antennas we use with our 915-MHz telemetry system. They vary in length, material, and shape. We will recommend an antenna based upon your animal mass, implant operating life, and implant type.

The 50-mm A and E antennas produce the strongest signal when implanted in rats. The 30-mm B and D antennas fit easily into mice without folding. The D and E antennas are made with a thinner stranded wire. We can fold the 30-mm D antenna through 45 degress with a 1-g force, while the 30-mm B antenna requires a 4-g force. Because of their flexibility, the D and E antennas are a natural choice for mice and rats respectively. The A and B antennas are, however, more resistant to fatigue. For implantations longer than three months, we recommend the A and B antennas. We no longer make the C-Antenna because it transmits ten times less power than the loop antennas, while the D-Antenna is just as easily accommodated by a small animal as the C-Antenna.

Battery Life

[20-MAY-25] The battery life of Subcutaneous Transmitters (SCT) and Head-Mounting Transmitters (HMT) is a simple function of their sample rate and battery capacity, and lends itself to a simple calculation. The operating life of Implantable Stimulators (IST), however, is more difficult to estimate. On our IST page, you will find links to IST device manuals, where you will in turn find operating life discussed in detail in the manual's Battery Life chapter. The operating life of Implantable Inertial Sensors (IIS) is a strong function of the type of measurement it makes. Starting at our IIS page, select the manual of an IIS device and go to the Versions section for a table of battery life versus measurement and implant mass. In the following paragraphs, we describe how the operating life of SCTs and HMTs can be deduced from their mass and sample rate.

The operating life of an SCT or HMT is how long it takes to consume its battery capacity in its active state. The shelf life is how long it takes to consume 10% of its battery in its sleep state on the shelf. To obtain the operating life of a device, we divide its battery capacity by its active current cosumption. We wish to provide our customers with a minimum operating life so they can plan their experiments with confidence. We combine the battery capacity, C, with a maximum active current we obtain with a formula particular to each device family. Here are the equations we use to obtain the maximum active current for the A3048, A3049, and A3047 families of SCTs, as well as the A3040 family of HMTs.

Where I_a is the maximum active current and R is the total sample rate. For units we use microamp (μA) and samples per second (SPS). A four-channel HMT with all channels running at 256 SPS will have R = 1024 SPS, so I_a = 148 μA.

The sample rate required by each input of a transmitter will, in almost all cases, be proportional to the input channel bandwidth. We add the sample rates of all channels together to obtain the total sample rate, R. If, for example, we have four channels with bandwidth 80 Hz, 40 Hz, 40 Hz, and 160 Hz, the sample rates will be 256 SPS, 128 SPS, 128 SPS, and 512 SPS respectively. The total sample rate will be 1024 SPS.

Figure: Operating Life vs. Total Sample Rate for Versions of the A3049 SCT by Mass.

The larger the battery, the larger its capacity. Manufacturers express the capacity of their lithium batteries in mA-hr (milliamp-hour). For our purposes, μ-Ady (microamp-day) is a more convenient unit. We have 1 mA-hr (milliamp-hour) = 1000 μ-Ahr (microamp-hour) = 42 μ-Ady (microamp-day). The following table gives the approximate mass of SCTs, ISTs, IISs, and HMTs for various battery capacities.

When an SCT is in its sleep state, which we also call "turned off" or "inactive", its consumes roughly 1 μA from its battery. The shelf life of an SCT is 10% of its battery capacity in microamp-days (μA-dy) divided by 1 microamp (1 μA). The A3049A3 is equipped with a CR1225 with capacity 2000 μA-day. Shelf life is 200 days, but we usually say six months. The HMTs do not have a sleep state. When their battery is in, the HMT is running. It runs until the battery is exhausted, and then it turns off. When we store an HMT on the shelf, we store it without a battery, so it is off and its shelf life is unlimited.

All our implantable devices are equipped with non-rechargeable, lithium primary cells. We experimented with rechargeable implants for several years and found them to be unreliable, toxic, and vulnerable to corrosion. They are unreliable becasue we cannot guarantee that our customers will connect the charging circuit correctly, nor that they will check the state of the battery before re-implantation. They are toxic because they emit gases when they are discharged. They are vulnerable to corrosion because the battery expands and contracts, which cracks its epoxy encapsulation, creating cavities in which water can condense. Our collaborators lost many animals to unresponsive rechargeable transmitters. Furthermore, rechargeable cells provide one third the charge capacity per unit volume of non-rechargeable cells. If we want to re-use transmitters because we absolutely do not want to buy new implantable transmitters for each experiment, we can deploy a Head-Mounting Transmitter (A3040, HMT). The HMT mounts on an animal using a connector that is cemented permanently to the skull. We can remove the HMT and replace its coin cell battery in a few minutes. We sell HMTs with a one-year warranty against unfortunate accidents that destroy the device.

Faraday Enclosures

[29-JUN-18] Faraday enclosures ensure robust reception from implanted transmitters. They also make sure that the telemetry system conforms to all local radio frequency regulations, because the enclosure keeps our telemetry signals contained within its walls. We describe the development of our enclosures in Faraday Enclosures. A single FE3A bench-top enclosure, with a transparent shelf installed, accommodates six animal cages and provide recording from at least forty cohabiting animals. A single FE5A canopy enclosure accommodates an entire rack of eighty individually-ventilated cages. Not only is radio-frequency interference kept out of the enclosure, but so is low-frequency electrical noise such as mains hum. Conversely, the transmitter signals are confined within the enclosure. The signal power outside the enclosure is too weak for detection by standard instruments, which guarantees that the system violates no local radio-frequency transmission rules. Furthermore, we can operate multiple recording systems in the same room, because their signals will not interfere with one another.

Soundproofing

[25-JUN-19] We may want to isolate our animals from sounds generated outside our recording system. According to our measurements, the steel mesh walls of our faraday enclosures do not provide attenuition of sound in the range 200 Hz to 40 kHz. Clear vinyl sheet, however, is an excellent absorber of the ultrasonic frequencies audible to rats and mice. A curtain of overlapping vertical strips of vinyl provides a factor of one hundred reduction in the power of ultrasonic waves, while at the same time allowing ventilation.

Implantation

Acknowledgement: Every detail of implantation in this section comes directly from our customers. We thank them for answering our questions. We do not mention our customers by name in our public documents, out of respect for their privacy.

[20-MAY-25] As a rule of thumb, mice and rats will tolerate an implanted device indefinitely provided that the implant mass is no more than 10% of the mass of the animal itself. A juvenile or pup animal will tolerate an implant of up to 15% of its body mass for several days, after which it will have grown sufficiently that the implant mass is less than 10% of its body mass.

A implantable device, its leads, and any head fixture attachments must well-secured and well-tolerated by the animal if the implantation is a success. Both the volume and the mass of the implant are important, but all our telemetry implants have density close to 2 g/cc, so we will talk only of the mass of the devices. Most strains mice are roughly 10 g after 3 weeks and 20 g after 6 weeks. Our A3048S transmitters weigh 1.9 g and they are tolerated by mice 15 g and larger. Our A3049H transmitters are 2.9 g and they are tolerated by mice 20 g and larger. Male Sprague-Dawley rats reach 300 g at 8 weeks, while females reach 300 g only after 16 weeks. Our A3049D transmitters are 6.0 g. They are well-tolerated by rats of 80 g. Our A3049L transmitters are 14 g. According to one implanter, the A3049L is not tolerated by smaller rats, and even when implanted in a 300-g rat, if the transmitter is placed too far to the posterior, over the femoral region, the rat will be so irritated by the transmitter that it will scratch right through its skin.

One of our collaborators measured the weight of four 28-day-old rats before and after implantation of a 2.6-g transmitter. The animals weighed as little as 55 g at the time of implantation. A control animal received no transmitter and was subject to no surgery. All five animals cohabited in the same cage in the week following, and we recorded EEG continuously from the four implanted transmitters.

Figure: Five Cohabiting P28 Rats (Click for Movie). Four have 2.6-g transmitters implanted using the two-incision method, one does not. Note the shaved areas around the incisions, and the stitches closing the incisions on the head and back. The transmitter is beneath the incision on the back. We run the leads under the skin to the incision in the scalp, where M0.5 screws act as electrodes through holes in the skull.

Weight gain following surgery is presented in the following table. See also Chang et al. for implantation procedure and EEG recordings. In Wright et al. the authors describe how mice of initial weight 18-22 g tolerated 2.6-g for at least three weeks to the satisfaction of UK veterinary inspectors.

Figure: Weight Gain in Young Rats After Implantation of A3019A in P28 Rats, 15-MAY-14. Control animal has no transmitter implanted.

You will find the latest implantation procedures described in informal documents Implantation_Wykes and Implantation_Silva. We describe older implantation procedures in detail in the supplementary materials of Chang et al, 2016, the first section of Wright et al, 2015, and in our original methods paper Change et al, 2011.

There are two established procedures for implantation. The two-incision procedure uses one incision in the back or side of the animal to accommodate the body of the transmitter, and a second incision in the scalp to give access to the skull. We tunnel the electrode leads under the skin to the skull. On the skull, we insert screws or wires into skull holes and fasten them in place with dental cement. Or we insert pins into depth electrodes, lower the electrodes into the brain, and secure with dental cement. The two-incision procedure works in all animals. The single-incision procedure uses one incision in the scalp large enough to slide the body of the transmitter down under the neck to the abdomen. This single-incision procedure works better in mice than in rats, because the distance the transmitter must be thrust under the skin is greater in rats.

In both procedurs, we have the option of closing the incision in the scalp, or building up a head fixture of dental cement and fastening the edges of the incision to the head fixture with cyanoacrylate. We recommend 3M RelyX Unicem 2 for dental cement and Vetbond for cyanoacrylate. Closing the incision creates tension in the scalp, which in turn invites irritation, scratching, and ultimately the opening of the scalp sutures. Leaving the incision open is the most common practice among our customers, but invites infection at the interface between the scalp and the dental cement. The scalp must be well-secured to the dental cement with cyanoacrylate and monitored for the duration of the experiment to make sure it remains secured to the cement. Any opening between the scalp and dental cement permits bacteria to penetrate the body. In particular, bacteria will migrate along the passage made by the transmitter's silicone leads, arrive at the transmitter body, where they cause swelling, fur loss, and eventually skin rupture.

When implanting, you may be working on steel tables with steel implements. These can be magnetized during their use, at which point they can turn on and off the transmitter while you are working. One way a table or a tool can become magnetic is by storing your on-off magnet on the table or the tool handle. Turning off and on the transmitter during implantation causes no harm to the transmitter, but can cause concern that the transmitter has failed when it has not. We provide large, stainless steel magnets called a cow magnets for use with magnetically-activated implants.

The choice of termination at the tip of the leads depends upon what we want to measure, as well as the size of the animal. You will find a list of currently-available terminations and electrodes in our Electrodes and Terminations manual. The most important consideration when implanting an electrode is that the conducting tip of the electrode must be fixed in place with respect to the body tissue as the animal is moving. If the electrode moves with respect to the brain or skull tissue, we will see step artifacts in our EEG recording. Our objective is to reduce the number of step artifacts we see from moving animals to the point where their frequency is has no significant impact upon our automated analysis of the signal. Our Event Classifier will be fooled by no more than 5% of step artifacts, so if we want the classifier to make mistake no more than one such artifact per day for an actual EEG event, we must reduce the frequency of such steps to fewer than one per hour.

Our first successful EEG electrodes were a stainless steel screw soldered to the end of the electrode lead. In mice, the skull is only 200 μm thick near the bregma. For EEG monitoring, we recommend a 0.6-mm long, 0.5-mm diameter threaded electrode. In rats, the skull is around 500 μm thick, and over the course of many weeks, will grow thicker. The screw we recommend for rats is 3.2-mm long and 1.5-mm in diameter. This screw is large enough to accommodate the growth of a young adult rat from 50 g to 200 g and still maintain good contact with the brain for consistent EEG amplitude throughout months of EEG recording. Nevertheless, soldered screws have the following disadvantages.

1. We would like to cut the leads to exact lengths during implantation. But this is not possible if we are using a soldered screw.
2. Turning a soldered screw into a skull hole while it is connected to a flexible lead is possible but difficult. There is a risk that the screw will snap off the lead while you twist it.
3. Replacing a soldered stainless steel screw requires skill with a soldering iron combined with acid flux to make the joint reliable.
4. Solder joints are not stainless: the tin and silver in the joint corrode in water and generate their own electrode potentials.

To record electrocorticography (ECoG), we recommend an angled bare wire secured in a skull-hole with a screw. The tip of the bare wire touches the surface of the brain, or if we make it slightly longer, it penetrates the brain by a fraction of a millimeter. We cut the leads to the correct length, we dry the skull before creating our head fixture, we prepare the skull with cyanoacrylate, we cover all exposed metal with dental cement, and we make sure the dental cement has time to cure before closing the incision. By these means, we obtain high amplitude with the bare wire tip, we reduce chemical artifacts by eliminating solder joints, and we reduce movement artifact by securing the wire with a screw.

Figure: Bare Wire Electrode with Fixing Screw. (Courtesy Robert Wykes, ION/UCL)

When we first receive an implant, we can ask for it to have A-Coils at the ends of its leads, so we will have 1-mm of bare steel coil at the end of each lead to work with. If we are re-using an implant, we will most likely have cut lead ends, so we must expose 1 mm of the coiled steel wire to create a new bare-wire electrod. We remove 1 mm of insulation by cutting through the silicone 1 mm from the lead end and unscrewing the detatched silicone from the lead. See Coiled Wires for videos of silicone removal. Once we have exposed 1 mm of coiled wire, we hold the insulated end of the lead with forceps and we grab the exposed wire with tweezers. We stretch and straighten the coil. We put a right-angle bend in the straightened wire and trim the bent section to the desired length. The bend will be at the edge of the skull hole. We trim the bent end to a length equal to the skull thickness plus the distance we want the tip of the wire to penetrate beneath the skull.

In rats, we recommend a straightened wire 5.0 mm long with the bend half-way along. In mice, we recommend a 2.4-mm wire with the bend half-way along. We place the bent tip of the wire in a skull hole and lay the insulated lead along the surface of the skull. We thread a screw into the hole. The exposed wire on top of the skull allows the screw to avoid interfering with the silicone insulation of the lead, and will allow dental cement to bond to the wire directly. In rats, the 2.5-mm wire passing through the skull will penetrate roughly 1.0 mm into the brain. In mice, the penetration of the 1.2-mm wire tip will be similar, because the skull is thinner. The wire is held in place by a screw. We cover the screw with dental cement. The cement anchors and insulates the head of the screw, and it bonds to the wire itself.

The coil will flex between the transmitter and the anchor screw, but the bare wire and the screw will be fixed with respect to the skull. Movement of the brain with respect to the skull will generate movement artifact, but such movements are rare and minimal. We will not see sudden jumps in our ECoG due to intermittent metal-on-metal contact. Nor will we see electromyogram (EMG) from muscles above the screw, because we have insulated the top of the screw with cement. A well-secured pair of electrodes produces zero or one step artifact per day, while poorly-secured electrodes will produce several artifacts per minute. Step artifacts make it more difficult to apply automatic algorithms that find spikes and seizures. When we come to securing the bare wire in the skull hole, we need tweezers to hold the screw, and a hand to turn the screwdriver. Somehow, we must keep the bent wire end at the edge of the skull hole while we insert the screw. Here is a description provided by one implanter of how she secures the lead temporarily.

"Usually I will put a small amount of cyanoacrylate glue in a small petti dish at the start of the surgery (something like vetbond or medbond). Then once IÕve done the burr hole and got the transmitter and place and the hook in the end of the lead, I will place the hook in the burr hole with forceps. Then if you pull down very gently (!) on the transmitter through the skin in the back and pull towards the tail of the animal, it holds the lead in place (if your leads are the correct length). Then while holding like this with one hand, I place a small amount of glue to adhere the wire to the skull (away from the burr hole), with the other hand. By this time the glue becomes tacky as it has been exposed to the air since the start of the surgery. This means it dries quite quickly. Usually holding the transmitter down for around a minute is sufficient. Then you can let go and the lead (usually) stays in place. Then you have both hands to add the screw in place."

Here is a suggestion from another implanter about the placement of screws and covering with cement. "Make sure neither screw is anywhere near muscles and that the screws and about half a centimeter of wire coming from the exposed lead is also covered by dental cement so that neither moves at all. I also make completely sure that the cement is very hard before suturing the back incision where the transmitter is so that there is no chance of anything moving before the cement dries."

When we retrieve the transmitter from the animal, we tend to cut the leads where they emerge from the skull cement. It is possible to dissolve dental cement with acetone, as we describe in Silicone and Solvents, but usually the animal's brain is needed intact for examination, so we must cut the leads where they emerge from the head fixture. Having cut the leads, we remove silicone from the tips to expose more wire, as we describe above.

Rats and mice scratch at incisions and other points of irritation. The electrode leads of the transmitter, running from the back to the skull beneath the skin of the neck, will irritate the animal if they are poorly routed or if they are too rigid or thick. The diagram below shows us how not to route the wires in a rat, and how best to route the wires in a rat.

Figure: Correct Routing of Electrode Leads In Rats.

When the wires were routed directly up the top side of the neck, half the rats scratched the leads out of their skin, which is an indication of intense discomfort on their part. When the wires were routed along the side of the neck, with enough slack, none of the rats scratched the leads out.

If we want to inject an agent into the brain, and record EEG near the site of the injection, we can use a guide cannula to hold the bare wire in place, provided we insulate the wire from the steel shaft of the guide cannula with dental cement. If the steel wire touches the guide cannula, the EEG amplitude will drop because the steel guide has low electrode impedance. To provide insulation, we cover the bare wire with superglue, cut the end off to expose steel at the tip, bend by 90° and insert in the skull hole. We lower the guide cannula into the same hole, but separated by a few hundred microns from the bare wire, so they do not touch. The following diagram attempts to explain the arrangement.

Figure: Bare Wire Electrode with Guide Cannula.

The A3049 and A3047 SCTs come in versions that provide two or more channels each with their own reference, so that we can record potentials in different parts of the body. To record EEG, EMG, and ECG, for example, we need a three-channel transmitter with six leads.

Figure: One Second of Electrocardiogram from a Rat. Voltage range is 1 mVpp. From M1684813943.ndf. (Courtesy Aix-Marseille University)

To obtain the electrocardiogram (ECG) recording shown above, our collaborators developed the following method. Cut the ECG leads to the correct length, stretched the final 10 mm each lead, and cut around the insulation 5 mm from the tip. Once cut, the insulation pulls away from a 1-mm length of wire. They cover the tip with a silicone cap, which they hold in place with a 0/5 silk suture by squeezing the tip onto the lead. During surgery, they tie the exposed wire to the thoracic muscle with 0/5 sutures. One wire on one side of the heart, the other diagonally opposite.

Figure: Lead Prepared for Suturing to Thoracic Muscle. Photo courtesy of AMU.

To record electromyography (EMG), we have two methods recommended by implanters. In the first method, we straighten the wire, cut it back to 1 mm and insert it into the muscle. We insert the lead deep enough into the muscle so that all the exposed wire is enclosed by the muscle fibers. We do not want biopotentials from sources outside the muscle to reach our EMG electrodes. We secure the wire in the muscle with cyanoacrylate. We can add a suture to hold the insulated lead in place on the muscle surface as well, but a suture is an additional constraint placed upon the muscle itself, so we must be careful in the orientation and placement of the suture to avoid irritating the animal. We insert two such wires into one muscle to record EMG within that muscle. If we insert the two EMG leads in two separate muscles, our EMG will contain the potential difference between the two muscles, which is very likely to contain a strong component of ECG. In the second method, we put a 180° bend at the end of the wire to make a hook. We insert the hook into the muscle, then pull back to set the tip of the hook in the muscle fibers. Once again, we must make sure there is no exposed wire outside the muscle. Now we secure the wire in the muscle with cyanoacrylate. We can add a suture to fasten the lead in place as well, if we find that the hooks are coming loose without a suture. We place two such hooks in the muscle we want to monitor.

To record electrogastrogram (EGG), we use the same method, suturing the two electrodes to the gut. To record electromyogram (EMG), two methods are in use among our customers. One uses an incision and adhesive. We prepare 1-mm of bare steel helix at the end of each EMG lead. We make a 1-mm wide opening between muscle fibers in two places on the muscle. We use cyanoacrylate (superglue or vetbond) to fasten a helix into each slit. Cyanoacrylate bonds well to all animal tissue and to metal. The glue will hold the two coils in place between the muscle fibers. Another method is to secure a 1-mm helix to the exterior of the muscle with a suture, such as Ethicon Sutures Vicryl 5/0.

Explantation

[08-MAY-25] If we end our recording before we exhaust the battery of a transmitter, we have the opportunity to remove our telemetry sensor from our subject animal, clean the sensor, refurbish the ends of the leads, and implant again. We must take care when cutting the device out of the animal, especially if the existing implantation is more than a week old. Scar tissue builds up around the transmitter, holding in place, and wrapping around the antenna and leads. The leads are brightly-colored, but the antenna can be hard to see. The lead tips may be bound in place with dental cement. We can cut the leads where they enter the cement, then refurbish the lead tips by removing silicone to expose the bare steel wire, as we describe in Insulation Removal. If we are want to attach a screw or pin to the steel wire, we will need acid flux and a hot soldering iron, as we describe in Solder Joints. Attaching our own pins and screws is hard. If we would rather save the existing pins and screws, we must remove the cement with the lead ends embedded. To remove the cement, we and soak the leads and sensor in 20°C acetone for six hours. The cement will dissolve. The silicone of the sensor and leads will absorb acetone, but not so much as to cause significant damage to the structure of the silicone. As we describe in Silicone and Solvents, we must wash twice with clean acetone after dissolving the cement, so as to remove all traces of cement residue from the silicone surface. Once the sensor and leads are clean, leave them in air for twenty-four hours so that the acetone held by the silicone will evaporate. Store your explanted transmitters in a dry place. Do not store in water or any other fluid, nor in ethanol or acetone vapor.

Accelerated Aging

[04-FEB-25] Corrosion is the primary cause of failure for implanted transmitters. Epoxy is water-proof, but it is permeable to water vapor. Any cavities in the epoxy will eventually be filled with condensed water. Our encapsulation process is designed to reduce the number of cavities, but we cannot eliminate all cavities. Any residue of solder flux remaining on the circuit board after cleaning provides a space for water to condense and dissolve the residue, creating a surface layer that can conduct electrical charge so as to promote corrosion. Even if there were no cavities in the epoxy, electrical components themselves will eventually corrode in warmth and 100% humidity. Ceramic capacitors, in particular, are prone to cracking during manufacture, assembly and handling. In the warmth and humidity of an animal's body, microscopic cracks in ceramic capacitors corrode until they create an electrically conducting path between the capacitor plates.

We measure the corrosion resistance of every batch of transmitters we produce. We do this by destructive testing of surplus transmitters. If we are shipping twenty transmitters, we will make twenty-four. When all are ready, we will choose two, turn them on, place them in a sealed jar of water, and poach them at 60°C in our oven. We check them every day to see if they are still performing perfectly. If, after one week, they are still running perfectly, we ship the rest of the batch to our customer. If one of them fails, we will re-make the batch and warn our customer of a delay.

Figure: Corrosion Acceleration versus Corrosion Activation Energy (eV). We plot the acceleration at 60°C compared to animal body temperature 37°C.

The poaching is an accelerated aging test for corrosion. According to statistical mechanics, the rate at which a chemical reaction proceeds is proportional to e^−E/kT, where T is absolute temperature, E is the activation energy of the rate-determining step in the chemical reaction, and k = 8.6×10⁻⁵ eV/K is the Boltzmann constant. In Hallberg and Peck, the authors show that this relationship applies well to measurements of mean time to failure for temperatures 20-150 °C, relative humidity 20-100%, and activation energy 0.9 eV. Our devices operate at the rodent body temperature of 37°C = 310 K. During our accelerated aging test at 60°C = 333 K, we expect an acceleration of ×10. We are unaware of any corrosion process likely to occur in our circuits that activates with energy less than 0.6 eV. We assume an acceleration of ×10, but we are certain it is at least ×5. One week poaching at 60°C is at least equivalent to 5 weeks implanted.

Appendices

[20-NOV-24] In the Appendix to our Telemetry Manual, you will find the following sections:

• Introduction
• Signal Path
• Bit Rate
• Message Encoding
• Interference
• Blocked Messages
• Missing Messages
• Bad Messages
• Corrupted Messages
• Collisions
• Encapsulation
• Corrosion
• Body Capacitance
• History