Cortical slow potentials and the occipital EEG in congenital blindness.

In a group of 7 congenitally blind adults, electroencephalographic occipital alpha rhythms were absent, but slow negative cortical potentials (CNV) were recorded over the visual cortex and were similar to those of normally sighted controls. Frontal and central CNV amplitudes, but not auditory evoked potentials or reaction times, were decreased significantly in the blind. The results confirm the presence of a developmental EEG abnormality following early blindness, and demonstrate the independance of slow potential generation from rhythmic 8--12 c/sec EEG activity in deafferented visual cortex. Non-sensory specific, event-related potentials such as the Contingent Negative Variation may prove to be useful psychophysiological probes of residual cortical function in brain regions which are deprived of primary sensory input.