Neurostimulator for Hippocampal Memory Prosthesis

In this chapter, we discuss the design, fabrication, and evaluation of a neurostimulator for generating neural code–based electrical stimulation pulses. We show that, through multiplexing, this system can deliver constant current biphasic pulses, with arbitrary temporal patterns and pulse parameters to 32 electrodes using one pulse generator. Furthermore, a stimulus artifact suppression component is integrated with commercial amplifiers for recording short latency neural response to stimulation for feedback control. The key of this feature is to use CMOS switches to disconnect electrodes from recording amplifiers during stimulation, while shorting the recording system to ground through another CMOS switch to suppress ringing in the recording system. It is crucial to pay close attention to the timing of the switches used to block and suppress the stimulus artifact as it should be determined by the electrochemical properties of the electrode. Furthermore, the timing and stimulus magnitude of each pulse depends on the application and should be controlled by inputs from an external source that takes feedback commands from neural response from the region of stimulation. In this chapter, the reader will learn how to implement this system with low-power and compact packaged microchips to constitute an effective, cost-efficient, and miniaturized neurostimulator. The reader will then learn how to evaluate the design in phantom preparations and then in rat hippocampus. This neurostimulator design is desirable in a variety of neural interface applications, particularly hippocampal memory prosthesis aiming to restore cognitive functions by reinstating neural code transmissions in the brain.