What Happens to the Auditory Brain Without Auditory Input?
Lomber, Meredith, and Kral (2013) report that when the human brain is deprived of one sensory modality, it may compensate with supranormal performance in alternate intact sensory systems. Human psychophysical studies of people who were "early-deaf" have demonstrated superior visual abilities, and in people who were "early-blind," enhanced auditory functions have been described. However, "a causal link between supranormal visual performance and the visual acuity in the reorganized auditory cortex has never been demonstrated."
Lomber, Meredith, and Kral designed studies involving cats to explore and address these issues. They demonstrated that "superior visual perceptual abilities in the congenitally deaf (cats) are based on the crossmodal reorganization of specific regions of auditory cortex…(thus demonstrating) a causal relationship…" Of note, the crossmodal effects were not evenly distributed across all regions of the deaf auditory cortex. Indeed, crossmodal effects occurred in an adaptive fashion in "regions whose functions are also represented in the replacement modality."
Importantly, the authors note that their work may impact the selection and candidacy of people who receive sensory implants, such as cochlear implants (CIs). That is, crossmodal reorganization may hinder the ability of the auditory cortex to process auditory information delivered through CIs. They report previous studies of deaf subjects with extensive crossmodal plasticity were the same patients least likely to benefit from CIs.
For More Information, References, and Recommendations
Cardon G, Campbell J, Sharma A. (2012) Plasticity in the Developing Auditory Cortex—Evidence from Children with Sensorineural Hearing Loss and Auditory Neuropathy Spectrum Disorder. Journal of the American Academy of Audiology 23:396-411.
Giraud AL, Lazard D, Lee HJ. (2011) Cochlear Implant Outcome and Functional Brain Organization in Deaf Subjects. Seminars in Hearing 32(2):142-146.
Karns CM, Dow MW, Neville HJ. (2012) Altered Cross-Modal Processing in the Primary Auditory Cortex of Congenitally Deaf Adults: A Visual-Somatosensory fMRI Study with a Double-Flash Illusion. The Journal of Neuroscience 32(28):9626-9638
Lomber SG, Meredith MA, Kral A. (2013) What is the Auditory Brain Doing in the Absence of Acoustic Input. Canadian Hearing Report.
Meredith MA, Allman BL. (2012) Early Hearing Impairment Results in Cross-modal Reorganization of Ferret Core Auditory Cortex. Neural Plasticity 2012. Article ID 601591.