Telemetry User Manual[22-OCT-24] Our telemetry sensors and stimulators are battery-powered devices designed for use with small animals. All of them use the same radio-frequency (RF) messaging system for transmitting information, so we can receive signals from all of them with the same telemetry receivers. Animals can be housed together or separately. A single telemetry receiver can record signals from dozens of sensors.
Our Subcutaneous Transmitters (SCT) are small, battery-powered devices designed for implantation beneath the skin of an animal. We turn them on and off with a magnet. Each SCT measures one or more biopotentials. Some measure temperature. All versions sample biopotentials with sixteen-bit precision and transmit the samples by radio waves. The batteries in these implantable devices cannot be replaced. Our Head-Mounting Transmitters (HMT) mount on the exterior of an animal. They have no on-off switch, but we can remove and replace their battery.
Our Implantable Inertial Sensors (IIS) transmit acceleration and rotation and turn on and off with a magnet. These devices are designed for implantation in animals or attachment to fish. Our Implantable Stimulator-Transponders (ISTs) hibernate when placed next to a magnet, but otherwise are activated and controlled by radio waves. The RF messaging system we use for transmitting commands to stimulators is distinct from the one our sensors use to transmit information, but it does use of the same antennas.
A Telemetry System consists of sensors, Faraday enclosures, receivers, and acquisition computer. The computer and receiver communicate with one another by TCPIP. We have two types of receiver. A coaxial antenna receiver gathers telemetry signals with antennas on the end of coaxial cables. A coil array receiver gathers telemetry signals with antennas fixed in an array on a platform. 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.
Our Faraday enclosures isolate the telemetry system from ambient RF 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.
The Telemetry Control Box (TCB-A16) provides sixteen antenna inputs to which we can connect up to sixteen Loop Antennas (A3015C) 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 containing shelving units holding animal cages. In each case, we can record from dozens of animals. 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.
Our SCT and HMTs will monitor electroencephalograph (EEG), local field potential (LFP), electrocardiogram (ECG) or electromyography (EMG) at frequencies down to direct current (DC) and up to 640 Hz. We describe the sources of EEG and LFP in The Sources of EEG. For recordings from live animals, see our Example Recordings page. We currently have three models of SCT in production, each of which is available in a large number of variants. The A3048 provides only one input channel Its amplifier provides gain of ×100 for frequencies up to 160 Hz. Our smallest SCT is the A3048P with volume 0.70 ml and mass 1.8 g. We mount the battery beside the A3048 circuit rather than on top of it, which results in the A3048 having greater surface area, while being both thinner and lighter. The A3049 provides two input channels. These may be configured to each use their own reference potential or to share a reference potential. The A4049 amplifiers provide gain ×100 at frequencies up to 640 Hz. The A3049 can be equipped with small batteries for use in mice, or large batteries for use in adult rats. The A3047 if a four-channel transmitter that incorporates its own temperature sensor. Each of the four inputs will operate with its own reference potential or a shared reference potential. The amplifiers provide gain ×100 up to 640 Hz, for which the sample rate is 2048 SPS. The A3047 is intended for use in adult rats.
The primary purpose of our telemetry system is to record biopotentials continuously for weeks at a time, 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. The A3049A3 provides two input channels that share the same reference potential, allowing EEG to be monitored in two locations. Its mass is 2.2 g, which fits comfortably into an adult mouse. It samples its Red and Yellow inputs at 512 SPS each, and its amplifiers provide bandwidth 0.3-160 Hz. It runs for 14 days. The Red and Yellow inputs share the same common terminal, which is the Blue input, so there are three leads emerging from the device, plus the antenna. The A3049B3 is the same mass as the A3049A, but provides only the Red input and runs for 24 days. The A3049D3 is electrically identical to the A3049A3, but equipped with a larger battery. It's mass is 5.8 g and its operating life is 81 days. The A3049E is also 5.8 g, but provides only the Red input and runs for 139 days. The A3047A3D-C is a 6.7-g device that provides four inputs, each with its own reference potential. It is is designed to record EEG (electroencephalogram) 0.0-160 Hz, ECG (electrocardiogram) from 2-80 Hz, EMG (electromyogram) from 2-40 Hz, and EGG (electrogastrogram) from 0.0-20 Hz simultaneously. It also provides a temperature measurement. It runs for 72 days. Note that any of our transmitters can operate either as an AC or DC sensor. The AC sensors include a high-pass filter at 0.2 Hz or 2 Hz. The DC sensors eliminate the high-pass filter and record all the way down to zero frequency.
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 Octal Data Receiver (A3027) provides eight 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 Octal Data Receiver 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 will provide robust recording from forty co-habiting animals.
Faraday enclosures and multiple antennas cannot overcome the most severe interference a crowded city can produce. In our laboratory, a 1-W interference source at range 1 m will cause 50% loss of signal from a moving transmitter in a faraday enclosure equipped with two independent antennas. By application of the inverse square law, we expect a 3000-W 900-MHz GSM base station 55 m away to be capable of similar disruption. The power emitted by a mobile phone base station spreads out like the beam of a flash-light. If you are nearby but below the station, you can receive less power than if you are farther away but at the same altitude, and if the station is on a neighboring building, you will receive more power than if it is mounted on your own building. If your recording room is less than 100 m from a base station, and directly in the path of its transmit beam, we will advise you on how to make sure your telemetry system will provide robust reception.
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. In the body of this report, we describe the performance and operation of our Subcutaneous Transmitter hardware. In places, the description is detailed and technical. Consult our terminology page for definitions of terms like RF, IF, LO, mixer, attenuator, dBm, and dB.
[03-JAN-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.
| Assembly | Name | Type | Description |
|---|---|---|---|
| TCB-A16 | Telemetry Control Box (TCB) | Coaxial Antenna | 16 antennas, telemetry reception, location monitoring, PoE. |
| TCB-B16 | Telemetry Control Box (TCB) | Coaxial Antenna | 16 antennas, telemetry reception, command transmission, location monitoring, PoE. |
| A3038 | Animal Location Tracker (ALT) | Coil Array | 15 coil antennas in 48 cm × 24 cm array, location tracking, PoE. |
| A3018 | Data Receiver | Coaxial Antenna | 1 antenna, telemetry reception, requires LWDAQ Driver. Discontinued 2016. |
| A3027 | Octal Data Receiver (ODR) | Coaxial Antenna | 8 antennas, telemetry reception, requires LWDAQ Driver. Discontinued 2022. |
| A3071 | LWDAQ Driver | TCPIP Interface | Required by all existing A3018 and A3027 receivers. |
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.
Here is a more complete list of electronic assemblies, including sensors and radio-controlled implants.
| Assembly Number and Manual Link | Assembly Name | Status |
|---|---|---|
| A3028 | Subcutaneous Transmitter | Discontinued |
| A3048 | Subcutaneous Transmitter, One Input | Active |
| A3049 | Subcutaneous Transmitter, Two Inputs | Active |
| A3047 | Subcutaneous Transmitter, Four Inputs with Temperature | Active |
| A3040 | Head-Mounting Transmitter, Four Inputs | Active |
| A3041 | Implantable Stimulator-Transponder | Active |
| A3035 | Implantable Inertial Sensor | Active |
| A30512 | Blood Pressure Monitor | Planned |
| A3015C | Loop Antenna | Active |
| A3039 | Coaxial Feedthroughs and Combiners | Active |
| FE3A | Bench-Top Faraday Enclosure | Discontinued |
| FE3B | Bench-Top Faraday Enclosure | Active |
| FE5A | Canopy Faraday Enclosure | Active |
| A3038 | Animal Location Tracker | Active |
| TCB-16A | Telemetry Control Box Telemetry Reception Only | Active |
| TCB-16B | Telemetry Control Box with Command Transmitters | Active |
| A3027 | Octal Data Receiver | Discontinued |
| A2071E | LWDAQ Driver | Active |
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.
[17-OCT-23] 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 for coaxial antenna system with Telemetry Control Box:
List of parts for coil array recording system with Animal Location Tracker:
List of parts for coaxial antenna recording system with Octal Data Receiver:
Assuming you have the above parts in hand, follow these steps. They will take you through the set-up of the hardware and software, so that by the end you will be able to record and analyze transmitter signals.
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.
[24-OCT-24] 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.
[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 batche of transmitters before shipping.
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.
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.
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.
The distortion of the X is dominated by random electronic noise. There are no significant peaks in the spectrum outside the fundamenta.
Note that the distortion generated by the new A3047, A3048, and A3049 transmitters is hundreds of time less powerful than that of their predecessors, the A3013, A3019, and A3028. The new transmitters sample their signals uniformly, thus eliminating the scatter noise present in earlier devices.
[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.
[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".
For an totorial on browsing recordings with the Neuroplayer, see our Neuroplayer Introduction video.
[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.
| Receiver | Payload (Bytes) |
Description |
|---|---|---|
| A3018 | 0 | Data Receiver, no payload |
| A3027 | 0 | Octal Data Receiver, no payload |
| A3038 | 16 | Animal Location Tracker, sixteen detector coil powers |
| A3042 | 2 | Telemetry Control Box, top power and top antenna |
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).
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.
[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.
| Lead Code |
Outer Diameter (mm) |
Spring Diameter (μm) |
Wire Diameter (μm) |
Resistance (Ω/cm) | Maximum Length (mm) |
Names |
|---|---|---|---|---|---|---|
| B | 0.7±0.1 | 450 | 100 | 6.3 | 280 | Thin Lead |
| C | 0.5±0.1 | 250 | 50 | 25 | 130 | Very Thin Lead |
| D | 0.8±0.1 | 500 | 150 | 1.6 | 130 | Stimulator Lead |
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.
[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.
[14-NOV-24] 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.
| Antenna Code |
Length (mm) |
Description |
|---|---|---|
| A | 50 | Stranded steel loop antenna, 360-μm diameter 7×7 304SS wire, insulated in clear MED-6607 silicone, for transmitters in rats. |
| B | 30 | Stranded steel loop antenna,
360-μm diameter 7×7 304SS wire, insulated in clear MED-6607 silicone, for transmitters in mice. |
| C | 13 | Straight antenna of helical wire, 450-μm diameter 316SS helix. Discontinued. |
| D | 30 | Stranded steel loop antenna, 250-μm diameter 7×7 304SS wire, insulated in clear MED-6607 silicone, for transmitters in small mice. |
| E | 50 | Stranded steel loop antenna, 250-μm diameter 7×7 304SS wire, insulated in clear MED-6607 silicone, for radio-controlled implants. |
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.
[24-OCT-24] The active current consumption of a transmitter increases linearly with the number of samples it transmits per second. Divide the capacity of the battery by the active current conusmption to get the maximum number of hours of operation the device can provide.
The operating life of a transmitter 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 batter in its sleep state on the shelf.
When a transmitter is in its sleep state, its magnetic switch consumes some current. In the A3049A, the sleeping current is around 0.8 μA. The A3049A3 is equipped with a CR1225 with capacity 2000 μA-day. Shelf life is around 250 days, but we usually say six months.
[09-FEB-24] 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.
[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.
[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.
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.
[15-AUG-24] 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, and assume that the density is close to 2 g/cc. Most strains mice are roughly 10 g after 3 weeks and 20 g after 6 weeks. Our A3048S transmitters weigh 1.9 g. They are tolerated by mice 15 g and larger. Our A3049H transmitters are 2.9 g. 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 5.8 g. They are well-tolerated by rats of 80 g. Our A3049L transmitters are 14 g. According to one implanter, the A3028L 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.
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.
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.
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.
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.
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.
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.
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.
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.
[13-MAR-24] 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.
[19-DEC-23] The cause of failure for implanted transmitters is corrosion in the 100% humidity of the animal's body. We encapsulate our transmitters in epoxy. Epoxy is water-proof, but it is permeable to water vapor. Once water vapor arrives at a cavity within the epoxy, it will condense and cause corrosion. Our encapsulation process is designed to eliminate cavities. Even if there are no cavites, the electrical components themselves can corrode. Ceramic capacitors in particular are prone to cracking during assembly and handling. In the warmth and humidity of an animal's body, these cracks will corrode until they cause a short-circuit between the capacitor plates.
We measure the corrosion resistance of our transmitters by means of accelerated ageing. For every ten transmitters we ship, we set aside at least one extra, turn it on, and place it in water in our oven at 60°C. Every day we take the transmitter out and check how it is doing. 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 ageing test at 60°C = 333 K, we expect an acceleration of ×10.
[20-NOV-24] In the Appendix to our Telemetry Manual, you will find the following sections.
