Neuroplasticity with cochlear implants: Underlying neuronal mechanisms

Chronic cochlear implant (CI) stimulation in congenitally deaf cats (CDCs) leads to cortical maturation matching imaging data from humans (Kral and Sharma, 2012, TINS). One possible measure of auditory plasticity is the reorganization of aural preference following monaural CIs (Kral et al., 2013, Brain), showing a sensitive period of <4.2 months in cats. A substantial reduction of binaural information following developmental unilateral hearing was found in cortical neurons (Kral et al., 2015, Audiol Neurootol). Consequently, auditory maturation requires experience. Additional to reduced synaptic plasticity, loss of acuity in feature representation, deficits in integrative function of the cortical column and deficits in corticocortical, particularly top-down, interactions, close the sensitive periods (Kral 2013, Neuroscience). Cross-modal plasticity recruits auditory resources for non-auditory tasks. Despite of cross-modal reorganization in some auditory areas the extend of the underlying reorganization of corticortical connections (Barone et al., 2013, PLoS One) indicates that this only moderately limits auditory processing capacity. Electrophysiological recordings in the dorsal auditory cortex of CDCs demonstrate that the cross-modally reorganized secondary auditory areas maintain a predominance of dormant auditory inputs additional to moderate cross-modal reorganization. [Supported by Deutsche Forschungsgemeinschaft (Cluster of Excellence Hearing4all).]