Cortical Neuroplasticity in Deafness

Sharma, A.

A remarkable ability of the human brain is neural plasticity, the brain?s dynamic capacity for change and adaptation. Sensory disorders such as congenital deafness prevent normal growth and connectivity in the brain-possibly resulting in deficits in oral language and cognition in deaf children. Cochlear implants (CI), bypass peripheral cochlear damage, by directly stimulating the auditory nerve and brain. Children who receive CI?s provide a platform to examine the trajectories and characteristics of experience-dependent plasticity in the central auditory system. In large-scale studies of deaf children fitted with cochlear implants, we have established sensitive periods for development of the central auditory pathways. Another important aspect of plasticity in deafness is the re-organization and re-purposing of auditory cortex by other sensory modalities known as cross-modal compensatory plasticity. Our high-density electroencephalographic (EEG) experiments using auditory, visual and somatosensory stimulation show activation of auditory cortical areas in response to visual and vibrotacticle stimulation, suggestive of cross-modal recruitment by the visual and somatosensory modalities. Our experiments show that deaf subjects who had greater difficulty understanding speech in noise via their cochlear implant showed greater evidence of cross-modal recruitment. Our results suggest that compensation for listening to degraded auditory input via a cochlear implant results in greater dependence on other modalities, which serves to aid communication in real-world situations. Our results indicate that the alterations in neural circuitry that underlie compensatory cross-modal plasticity in hearing loss may be an important source of variability in outcomes. Furthermore, by understanding neuroplasticity in deafness we may be able to customize rehabilitation programs tailored to individual needs.

Supported by the US National Institutes of Health.