Head-Mounting Transmitters (HMT)

The Head-Mounting Transmitter (HMT) is lightweight, multi-channel, wireless biopotential sensor that mounts on the head of a laboratory mouse. The HMT mates with an Electrode Interface Fixture (EIF) that we cement permanently to the animal's skull. The HMT is well-suited for recording EEG (electroencephalogram), but can also record EMG (electromyogram) from muscles in the animal's neck.

Our HMTs operate in pairs. Both HMTs in a pair are configured to use the same telemetry channel numbers, so that their signals appear identically in our telemetry recordings. When one HMT has nearly exhausted its battery, we replace it with the other. By exchanging HMTs every week, we can record four channels of EEG indefinitely from the same animal at with a 0.0-160 Hz pass-band. The signals transmitted by HMTs are identical to those transmitted by our Subcutaneous Transmitters (SCTs). They are picked up by the same telemetry antennas and transported by coaxial cables to the same telemetry receivers. Thus HMTs and SCTs can operate along side one another in the same telemetry system.

Although HMTs are re-usable, a strong mouse can pull one off and chew on the circuit until it is destroyed, so we must be prepared to replace them occasionally. The EIFs are not re-usable, so each new animal must be equipped with a new interface fixture. Because of the risk of one animal pulling an HMT off another, especially if the animals are epileptic, we recommend against co-housing animals equipped with HMTs.