MULTIUNIT RECORDING FROM REGENERATED BULLFROG 8TH NERVE USING IMPLANTABLE SILICON-SUBSTRATE MICROELECTRODES

Multi-microelectrode silicon devices were developed for extracellular recording from multiple axons in regenerated eighth cranial nerves of American bullfrogs. Each includes a photolithographically defined arra y of holes and adjacent metal microelectrodes. A device is implanted w ithin a transected eighth nerve; regenerating fibers grow through the holes en route to the brainstem. Multiple spike trains were recorded f rom two animals al up to 21 weeks after implantation. Single units wer e tracked for over 8 h. Some responded to sound with tuning typical of fibers innervating the amphibian and basilar papillae. Units of vesti bular origin also were recorded. Action potentials were 30-140 mu V P- P amid noise of 5-10 mu V RMS, an adequate signal-to-noise ratio for s pike detection and sorting. Histology confirmed that bundles of myelin ated fibers grew through holes near electrodes that recorded activity. The implantation success rate was low, due to surgical morbidity, dev ice extrusion, and lack of nerve regeneration through some devices. Fu ture designs will address these issues and incorporate transistor ampl ifiers on devices to increase signal-to-noise ratios. The potential of implanted silicon devices to simultaneously record from many axons of fers an opportunity for multicellular studies of auditory, vestibular and seismic signal processing in the vertebrate inner ear. (C) 1997 El sevier Science B.V.