Highly parallel recordings of unit and local field potentials with active and passive neural probes in freely-moving animals.

Abstract

The research presented in this dissertation demonstrates the application of state-of-the-art silicon neural probes to in-vivo extracellular neural recording. Sixty-four and ninety-six site active and passive probes were designed, fabricated, and used in acute and chronic in-vivo experiments. With these probes we have simultaneously monitored neural activity within multiple subregions of the rat hippocampus. High density field recordings were used to deduce the synaptic inputs to different hippocampal subregions, and single unit activity was isolated from many cells simultaneously. It was shown that on-chip probe circuitry offered significant advantages in these experiments. Buffering allowed the elimination of headstage preamplifiers, which are bulky and limiting in behavioral experiments. Further, it was shown that on-chip buffering helped to reduce the signal artifacts associated with animal movement. With active probes, high quality field and single unit recordings were obtained even during periods of vigorous animal movement. Circuitry for front-end-selection was used to reduce the amount of interconnect associated with these high-channel-count probes, allowing the isolation of large numbers of single units from sixty-four sites with only eight output channels. Finally, it was shown that on-chip test modes can be utilized to measure site impedance or monitor electrode integrity, with little or no additional cost in terms of interconnect or external equipment. The data gathered in these experiments demonstrates that high-channel-count neural probes can offer a unique glimpse into the physiology of neural systems. The isolation of large numbers of hippocampal place cells with these probes paves the way for future studies on temporal coding and neuronal interactions among place cells. In separate experiments, high-density field recordings were used to deduce the synaptic inputs to the dentate gyrus, CA1 and CA3 during gamma and theta rhythm in six freely moving rats. Because of their wide area and high density, these recordings have provided unique insight into the dynamics of neuronal activity during these important hippocampal rhythms. Finally, these results have encouraging implications for the development of motor cortical neural prostheses, which require a high density and stable extracellular neural interface for chronic implantation.