Expansion of the tonotopic area in the auditory cortex of the blind

Abstract

A part of the core area of the auditory cortex was examined in nine blind and 10 sighted individuals by magnetic source imaging and was found to be enlarged by a factor of 1.8 in the blind compared with the sighted humans. Moreover, the latency of the N1m component of the auditory-evoked magnetic response was significantly decreased in the blind. The development of use-dependent cortical reorganization may be a consequence of the absence of visual input in combination with enhanced auditory activity generated by the long-term concentration by blind individuals on nonvisual cues to interact appropriately with the environment. It is consistent with and well suited to mediate the demonstrated increased ability of the blind to accurately localize acoustic sources in peripheral auditory fields and to decode speech.

Figures

Fig. 1.

The change in signal power (a) and source location on the mediolateral axis (b) is shown as a function of stimulus frequency, averaged separately for the two groups. The bar graphs on theright illustrate that the effects [smaller signal power (NS) and expanded map size (p < 0.01) in the blind] can be observed equally in both hemispheres. The observation that the area across which the four different frequencies respond is larger in the blind whereas the signal power tends to be smaller suggests that the neuronal pool activated by a given sinusoidal tone is more specific in the blind than in sighted individuals. Error bars indicate SEs.