Wide-field Calcium Imaging for Evaluating Cochlear Implant Stimulation Strategies in the Auditory Cortex
Bruno Castellaro, Tony Yip Ka Wing, Fei Peng, Zeeshan Muhammad, Shiyi Fang, Israel Nelken, Jan Schnupp
Cochlear Implants (CI) are an effective neuroprosthesis for humans with profound hearing loss, enabling deaf adults to have phone calls without lipreading and babies to have successful language development. However, CIs have significant limitations in complex hearing situations, motivating the need for further research including in animal models. One major challenge in electrophysiology in CI animals lies in excluding the CI electric artifacts from the recording, since they are orders of magnitude larger than the amplitude of action potentials. To circumvent this problem, we have set up an imaging system allowing us to monitor neural activity in the auditory cortex (AC) of CI supplied rats using the Ca++ sensitive dye OGB-488. Here we describe an initial experiment with this setup, in which we recorded cortical responses to 4 different stimulation patterns which were delivered across 3 CI channels to the contralateral ear. We then investigated whether the discriminability of the AC response patterns(which we assume to be predictive of the perceptual discriminability of the patterns) depends on pulse rate (300 and 1800 pps were tested) and on whether or not pulses were delivered interleaved or simultaneously across channels. While pulse rate had only a very modest effect on the discriminability of the neural responses, the stimulation mode had a major effect, with simultaneous sampling, perhaps surprisingly, allowing much better pattern discrimination than interleaved sampling. The result suggests that allowing collisions of pulses on neighboring channels may not always be detrimental, at least if partial overlaps of pulses, in which anodic and cathodic pulse phases might cancel, are avoided.