Response Properties of Spiral Ganglion Neurons to Shaped Pulses in Electrical Stimulation

JIMENA BALLESTERO; KATIE SMITH; DANIEL JAGGER; JONATHAN LAUDANSKI; SØREN RIIS; DAVID MCALPINE

Baltimore

Congreso; 38th annual midwinter research meeting of the association for research in otolaryngology; 2015

Association for Research in Otolaryngology

BackgroundSpiral ganglion neurons (SGN) transmit tonotopically organized information from the hair cells to the central auditory system. In severe and profound hearing loss, SGNs can be directly electrically activated through cochlear implants (CI). A critical issue in CI, however, is the spread of electrical currentwithin the cochlea, such that individual contacts on the electrode array excite a broad swathe of the nerve fibres innervating the cochlea. Numerous strategies have been developed to overcome this issue that usually take into consideration the geometry of spread current. Here, we assess the responses of isolated SGNs to a novel electrical pulse shape, designed to take into account their biophysical properties.MethodsPatch-clamp recordings were made from SGNs in cultured mice (P10-P14). We characterized the biophysical properties of SGNs using current steps to study firing properties, and stimulation with families of voltage steps to study theirvoltage-dependent conductances. Additionally, we probed their sensitivity to current injections similar to those applied during CI activation. Thus, we applied square current pulses of 100μs duration and with different amplitudes. Finally, we tested a novel stimulation protocol based on the observation that SGNs can be sensitive to the slope of the stimulus input (Oertel 2009). To prove that this principle applies, a family of 100μs stimuli with different slopes were designed.SummaryWe report distinct populations of SGNs with different firing properties (fast adapting, slow-adapting and non-adapting) that varied in their thresholds to square pulses stimulation. By applying a novel stimulation protocol in which electrical pulses are shaped we find that increasing the slope of the stimulus modulate SGN firing in a manner similar to amplitude changes. Our data demonstrate that modulation of the slope of the stimulation current can modify SGN responses in a manner that alters their firing patterns, suggesting thatthis can be used as tool to modulate SGN responses in the context of electrical stimulation with CIs.