A novel telemetry system for recording EEG in small animals

It has become increasingly evident that continuous EEG monitoring is necessary to observe the development of epilepsy in animals, and to determine the effect of drugs on spontaneous seizures. Telemetric recording systems have been increasingly used to monitor EEG in freely moving animals. One challenge faced by such systems is to monitor frequencies above 80Hz continuously for weeks. We present an implantable, 2.4-ml, telemetric sensor that can monitor EEG at 512 samples per second for eight weeks in a freely moving animal. With minor modifications, the same transmitter can operate at higher sample rates with a proportional decrease in operating life. Signal transmission is through bursts of 915-MHz radio power. The burst transmission and several other novel techniques reduce the transmitter's power consumption by two orders of magnitude while allowing 8 transmitters to share the same recording system. The use of radio-frequency transmission permits digitization within the sensor to sixteen-bit resolution, thus eliminating transmission-generated signal noise. The result is a signal with dynamic range 9mV, bandwidth 160Hz, input noise 12μV, and AC power interference less than 1μV. All circuit diagrams are open-source. Data acquisition takes place over the Internet using open-source software that works on multiple operating systems. The resulting system permits long-term, continuous, monitoring of EEG signals, therefore providing continuous and reliable data upon which to base studies of epilepsy in freely moving animals.