Simultaneous Wireless Electrophysiological and Neurochemical Monitoring

Information processing and propagation in the central nervous system is mostly electrical in nature. At synapses, the insulating gaps between neurons, electrical signals cause the release of chemical messengers called neurotransmitters which travel across the synapse and modulate the postsynaptic neuron electrical activity. The interrelated nature of these signals and their implication in several clinical and basic neural pathways motivate their simultaneous monitoring. We present an integrated system for continuous acquisition of both data modalities in awake behaving rats. It features one channel each of a configurable electrophysiological and a neurochemical acquisition system. The electrophysiological system comprises of a 40 dB gain fully differential amplifier with tunable bandwidth from 140 to 8200 Hz. The amplifier offers noise below 2 μVrms for all bandwidth settings. The neurochemical module features a picoampere sensitivity potentiostat with a dynamic range spanning 6 decades from picoamperes to micoamperes. Both systems have independent on-chip configurable ∆Σ ADCs with programmable digital gain and resolution. The system was also interfaced to a wireless power harvesting and telemetry module capable of powering up the circuits, providing clock for ADC operation and telemeter out the data at up to 32 kbps over 4 cm with a bit error rate (BER) < 10. Characterization and experimental results from both the electrophysiological and neurochemical modules as well as the full system are presented.