DIFFERENT CORTICAL ACTIVATION PATTERNS IN BLIND AND SIGHTED HUMANS DURING ENCODING AND TRANSFORMATION OF HAPTIC IMAGES

In this study, we investigated whether the occipital cortex of blind h umans is activated during haptic perception and/or transformation of a haptic image. Slow event-related brain potentials were monitored from 18 electrodes in 12 sighted and 15 congenitally blind participants wh ile they were engaged in a haptic mental rotation task. In both groups , slow negative shifts appeared over (a) the frontal cortex at the beg inning of each processing episode, (b) the left-central to parietal co rtex during encoding and maintaining of a haptic image, and (c) the ce ntral to parietal cortex during image transformation. A pronounced slo w negative potential over the occipital cortex emerged only in the bli nd individuals and was time-locked to the processing epochs. Its ampli tude increased with the amount of processing load. The slow wave effec ts observed in the blind individuals could indicate that occipital are as participate in specific, nonvisual functions or they could reflect a coactivation of these areas whenever the activation level of task-sp ecific processing modules located elsewhere in the cortex is raised by nonspecific thalamocortical input.