A morphometric analysis of auditory brain regions in congenitally deaf adults

We investigated whether variation in auditory experience in humans during development alters the macroscopic neuroanatomy of primary or auditory association cortices. Volumetric analyses were based on MRI data from 25 congenitally deaf subjects and 25 hearing subjects, all right-handed. The groups were matched for gender and age. Gray and white matter volumes were determined for the temporal lobe, superior temporal gyrus, Heschl's gyrus (HG), and the planum temporale. Deaf and hearing subjects did not differ in the total volume or the gray matter volume of HG, which suggests that auditory deafferentation does not lead to cell loss within primary auditory cortex in humans. However, deaf subjects had significantly larger gray matter–white matter ratios than hearing subjects in HG, with deaf subjects exhibiting significantly less white matter in both left and right HG. Deaf subjects also had higher gray matter–white matter ratios in the rest of the superior temporal gyrus, but this pattern was not observed for the temporal lobe as a whole. These findings suggest that auditory deprivation from birth results in less myelination and/or fewer fibers projecting to and from auditory cortices. Finally, the volumes of planum temporale and HG were significantly larger in the left hemisphere for both groups, suggesting that leftward asymmetries within “auditory” cortices do not arise from experience with auditory processing

Crossmodal reorganization in the early deaf switches sensory, but not behavioral roles of auditory cortex

It is well known that early disruption of sensory input from one modality can induce crossmodal reorganization of a deprived cortical area, resulting in compensatory abilities in the remaining senses. Compensatory effects, however, occur in selected cortical regions and it is not known whether such compensatory phenomena have any relation to the original function of the reorganized area. In the cortex of hearing cats, the auditory field of the anterior ectosylvian sulcus (FAES) is largely responsive to acoustic stimulation and its unilateral deactivation results in profound contralateral acoustic orienting deficits. Given these functional and behavioral roles, the FAES was studied in early-deafened cats to examine its crossmodal sensory properties as well as to assess the behavioral role of that reorganization. Recordings in the FAES of early-deafened adults revealed robust responses to visual stimulation as well as receptive fields that collectively represented the contralateral visual field. A second group of early-deafened cats was trained to localize visual targets in a perimetry array. In these animals, cooling loops were surgically placed on the FAES to reversibly deactivate the region, which resulted in substantial contralateral visual orienting deficits. These results demonstrate that crossmodal plasticity can substitute one sensory modality for another while maintaining the functional repertoire of the reorganized region

Adult deafness induces somatosensory conversion of ferret auditory cortex

In response to early or developmental lesions, responsiveness of sensory cortex can be converted from the deprived modality to that of the remaining sensory systems. However, little is known about capacity of the adult cortex for cross-modal reorganization. The present study examined the auditory cortices of animals deafened as adults, and observed an extensive somatosensory conversion within as little as 16 days after deafening. These results demonstrate that cortical cross-modal reorganization can occur after the period of sensory system maturation