EVENT-RELATED POTENTIALS DURING AUDITORY AND SOMATOSENSORY DISCRIMINATION IN SIGHTED AND BLIND HUMAN-SUBJECTS

The objective of the present study was to test if and to what extent p hasic and tonic event-related potentials of the human EEG may reflect phenomena of cortical plasticity. In particular, it was tested if the occipital cortex of blind subjects participates in the processing of n on-visual stimuli. To this end, 12 blind and 12 blindfolded sighted su bjects were tested in an auditory and a somatosensory discrimination t ask with 2 levels of discrimination difficulty. Slow and fast event-re lated potentials were recorded from 18 scalp electrodes. In addition t o the negative slow waves found in sighted subjects over frontal and c entral sites during auditory and somatosensory discrimination, a prono unced negative wave was revealed in the blind also over occipital brai n areas. These negative shifts were time-locked to the train of stimul i which had to be monitored with sustained attention, i.e. they rised and resolved with the beginning and the end of a 20-s discrimination t ime epoch. The P300 complex, on the other hand, which is a slow positi ve deflection over the posterior part of the scalp and which follows r are and task-relevant events 200-800 ms after stimulus onset was signi ficantly smaller at occipital electrodes in the blind than in the sigh ted subjects. Combined with neurophysiological and neuronanatomical ev idence originating from studies with visually deprived animals, these data suggest that the occipital cortex of blind human subjects is coac tivated whenever the system is engaged in a task which requires sustai ned attention and is less effectively inhibited at the end of a percep tual time epoch. In total the data cast doubt on the hypothesis that t he occipital cortex of blind subjects participates in modality-specifi c non-visual information processing.