Spatiotemporal neural interface dynamics elucidated with multi-channel electrochemistry.

Advances in neural probe technology continue to provide remarkable insights into neurological function and health. Multi-channel electrophysiological recordings of spikes and field potentials are the archetypical methods for extracting and decoding how neurons process information. However, as drug therapies continue to show efficacy at treating neurological disorders, understanding the chemical pathways underlying these disorders and treatments becomes all the more important. Current chemical sensing technologies rely on single point measurements. The following studies involved developing a series of implantable probes for the selective and simultaneous electrochemical detection of ions, neurotransmitters, and cellular structures across microscale regions of the brain. The first study examined the spatiotemporal response of extracellular pH (pH) in brain tissue around an inserted microelectrode array. The pH e data supported the hypothesis that faster implantation rates limit the spatiotemporal duration of acidosis around a device. These recordings provide a new mode of in vivo diagnosis to manage surgical brain trauma. The second study developed a novel probe technology for concurrently recording spatiotemporal dopamine overflow, unit spikes, and local field potentials at multiple locations within the brain. Recordings showed that the concentration and duration of electrically evoked dopamine overflow in the striatum correlated with suppression of beta-band activity (12-25 Hz). Measurements also demonstrated significant modulation of neuronal firing activity that temporally paralleled extracellular dopamine levels. These results have relevance to dopaminergic neurological disorders, such as Parkinson's disease. The third study investigated the application of short voltage pulses at microelectrodes to 'rejuvenate' unit-spike recordings at chronically implanted probes. Electrochemical impedance spectroscopy measurements fit to an equivalent circuit model showed that a spatiotemporal decrease in extracellular resistance following voltage pulsing correlated with a decrease in recording noise. This 'rejuvenation' procedure can be a useful intervention strategy to prolong the functional lifetime of chronically implanted microelectrodes. The experiments, while diverse, demonstrate an intriguing degree of dynamic neurochemical and cellular heterogeneity that has implications for neurological injury, disorders, and repair. Such findings provide strong impetus to incorporate implantable micro-scale electrochemical sensor arrays, or at least the knowledge they provide, into the development of diagnostic and therapeutic tools to interface with the brain.PhDApplied SciencesBiomedical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126454/2/3253302.pd