Neuroplasticity and early cochlear implant use in adult-deafened humans and rats

We hypothesize neuroplasticity in central auditory pathways play a key role in cochlear implant outcomes. Following initial cochlear implant activation, we track psychophysical abilities (spectral discrimination) in both adult-deafened humans and rats and relate these measures to speech perception (humans) and sensory encoding in the auditory cortex (A1, rats).In humans, we sent newly implanted subjects (N=3) home with a tablet and tracked spectral (quick-spectral modulation detection, QSMD) and temporal acuity (modulation-detection test, MDT). Speech perception was tested in-lab (CNC 30). Over the first ~30 days of implant use, we found improvements in frequency acuity 2 of 3 subjects speech perception in the same 2 of 3 subjects.In rats, we performed intercranial Electroencephalography (iEEG) recordings of the auditory cortex (A1) of normal hearing (N=7) and deafened rats (N=7). Tone and cochlear implant-evoked responses were evoked on a trial-by-trial basis. Reducing responses to a preferred frequency map revealed cochleotopic encoding of both tone-evoked and CI-evoked stimuli.We also trained rats on a 2-alternative forced choice (2AFC) task for sound frequency discrimination in NH (N=18) and deafened rats with cochlear implants (N=5). Rats were successful at 2AFC (d’>1) after ~3 weeks of acoustic training and, after deafening, ~1 week of cochlear implant training. Whole cell recordings revealed cochlear implant-evoked excitatory and inhibitory postsynaptic potentials in A1 were less correlated in untrained compared to 2AFC trained rats.We found cochlear implant use relates to improved speech perception and spectral discrimination in humans and spectral discrimination and cortical encoding (A1) in rats.