Auditory cortical plasticity under operation: reorganization of auditory cortex induced by electric cochlear stimulation reveals adaptation to altered sensory input statistics

We introduce a framework based on plastic-adaptational processes for an interpretation of electrical cochlear implant (CI) stimulation. Cochlear prostheses are used to restore sound perception in adults and children with profound deafness. After providing a review of cortical plasticity, we summarize our findings using optical imaging of intrinsic signals to map cat auditory cortex (AI) activated by CI stimulation. In adult AI of neonatally deafened animals, the acoustic deprivation caused a severe distortion of cochleotopic maps. A three-month period of CI-stimulation using the continuous interleaved sampling strategy did not re-install the status typically found in normal adults, but resulted in the emergence of a new topographical organization characterized by large, joint representations of all stimulated electrode sites. We suggest that the effectiveness of CI-stimulation relies primarily on a re-learning of input pattern arising from "artificial" sensory inputs via electrical stimulation, thereby supporting the importance of learning and training for the interpretation and understanding of the effects of CI stimulation. We suggest that the ability for gaining/ re-gaining speech understanding mediated by CI-stimulation is accomplished by new strategies of cortical processing due to enhanced cooperativity among large populations of neurons that serve higher processing stages to interpret new patterns arriving from the periphery. These strategies are thought to emerge from adaptational capacities in response to the constraints imposed by the properties of the new input statistics that in turn result from the stimulation strategy employed.