Topographic differences of slow event-related brain potentials in blind and sighted adult human subjects during haptic mental rotation.

Twelve blindfolded sighted, nine congenitally blind, and seven adventitiously blind subjects were tested in a haptic mental rotation task while slow event-related brain potentials in the EEG were recorded from 17 scalp locations. The overall topography of the slow wave pattern which prevailed during the task differed for sighted and for blind, but not for congenitally and adventitiously blind subjects. While the tactile stimuli were encoded, the blind showed a pronounced occipital and the sighted a pronounced frontal activation. The task-specific amplitude increment of a negative slow wave which can be understood as a manifestation of the process of mental rotation proper, showed a different topography for sighted and for blind subjects too. It had its maximum over central to parietal cortical areas in both groups, but it extended more towards occipital regions in the blind. In both groups, the effects were very similar to those observed in former studies with visual versions of the mental rotation task, i.e. the slow wave amplitude over central to parietal areas increased monotonously with an increasing angular disparity of the two stimuli to be compared. These results are discussed with respect to the question of whether visual deprivation in the blind can cause a reorganization of cortical representational maps.