A multichannel, wireless telemetric microsystem for small animal studies

Conventional means of collecting biophysiological parameters in small animals often involve cumbersome direct wiring and/or restraint of the animal. At present, there is no system for very small animals that can provide multichannel monitoring of biopotentials without restraining the animal or small enough in size or light enough in weight for studies with smaller animals. For larger animals, such as monkeys or larger rodents, systems have been proposed where the transmitter of the system has dimensions such as 2.5×2.5×1.3 cm³ and the weight is 9 g; this is far too high for smaller animals. Also, the battery life of that system is relatively short (∼10 h). In this study, a multichannel wireless telemetric microsystem for biopotential monitoring in small animals, such as mice or rats, has been designed, fabricated, and evaluated. This microsystem has four input channels with one calibration channel. There are 8 channels on the chip, of which five, the four electroencephalogram (EEG)/electromyogram (EMG) channels, and the calibration channel, are now in use. The system can also be expanded to more than eight input channels, if desired. In that case, a larger ASIC chip and larger circuit substrate might be required, depending on the type of biopotentials being measured. The amount of ASIC and circuit substrate space consumption is larger for biopotentials such as EEG or EMG than for others such as temperature or pressure. However, the same clocking-demodulation system could be retained up to ∼128 channels. The multichannel telemetric chip for the present embodiment is approximately 2×2 mm, and the overall size of the microsystem is approximately 10×10×5 mm, including the enclosure package and battery, with a total weight of 1 g. The power consumed by this four-channel version, where two channels are EEG and two are EMG, is ∼0.41 mW, and the fabrication process is AMI_ABN. There is a magnetic on/off provision. The microsystem has been used to monitor EEG, Theta activity, and nuchal EMG in mice with excellent results. This wireless telemetric microsystem can be effectively used to record multiple biopotentials from freely moving small animals. This platform microsyste- m can be extended to include other physiological parameters, such as temperature, pressure, and biological parameters.