Animal Location Tracker

Overview

[24-JUN-24] In addition to recording telemetry signals, our Animal Location Tracker (ALT) measures the activity and proximity of animals living in a cage by monitoring the movements of the Subcutaneous Transmitters (SCTs) implanted in their bodies. We place the cage on the ALT platform, and the array of detector coils within the platform measure the power received from each SCT separately. The distribution of received power across the coil array allows us to obtain a power centroid location for each SCT above the platform. The power centroid gives us a shrunken and distorted view of the locations of the animals. As an animal moves steadily across the platform, it's apparant position will surge forward, veer to either side, and pause. Distorted and innacturate as it may be, the power centroid provides us with a robust measurement of activity, direction, and proximity. By activity we mean the distance moved by the animal in a given time, perhaps per second or per minute. By direction we mean the direction in which the animal moves. By proximity we mean the average separation of each pair of animals in the cage. By means of activity, direction, and proximity, we can tell when an animal is asleep, when it is active, and whether or not it socializes with the other animals or remains on its own. We can tell if the animal is rotating clockwise or anticlockwise. If we have video blob-tracking of several animals in a cage, we can use the direction measurement to determine which animal contains which SCT, thus allowing us to identify and follow each animal in the video.

Figure: Animal Location Tracker, Version A3038C. A 48 cm × 24 cm array of coils provides telemetry reception and animal location tracking. Two mouse toys show scale. White lights on left edge show reception from two data channels.

An ALT makes it possible to watch and identify co-habiting and socializing animals, while the implanted SCTs provide simultaneous EEG recording from the watched animals. Fully-automated analysis of animal activity and social interaction may now be performed along with fully-automated event detection in EEG, such as automated association of spike-waves with decision making or seizure spikes with convulsions.

Figure: ALT System with 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 SCTs (7).

Video tracking software, such as our own VBT or Noldus's Ethovision XT, applies blob-tracking to video so as to obtain the coordinates of each animal in the field of view. But none of these blob-tracking algorithms can tell us which animal is which. When there are two or more animals in the field of view, the blob-tracking quickly loses track of the animal identities when they come together or move through enrichment features present in their cages. The ALT provides us with a real-time movement vector for each animal. By correlating these movement vectors with those provided by the blob-tracking, we can identify which blob corresponds to which SCT. We call this ALT function video disambiguation. We claim the ALT is necessary for automated tracking of more than one animal in a cage.

If all we need is a relative measurement of activity, this being the distance moved by each animal in a certain period of time, the ALT's measurement is sufficient. When our customers compare the activity measured by Ethovision XT to the activity measured by our ALTs, we find that the two are synchronized in time and very close to proportional in magnitude.

Animal Location Tracker

Overview

Further Reading