The physiological basis of visual hallucinations after damage to the primary visual cortex.

We used functional magnetic resonance imaging to examine the neuroanatomical correlates of visual hallucinations in a patient with a left visual field defect who had suffered bilateral occipital infarction. By cross-correlating the functional magnetic resonance imaging data with the hallucination events, we were able to identify the cerebral activity underlying the hallucinations. Bilateral activation was observed during visual stimulation in the calcarine fissure and the same activation was found medially in the left and right occipital cortex adjacent to the infarcted areas. This pattern of perilesional visual cortex activation is consistent with the suggestion that primary sensory areas may be involved in visual hallucinations after stroke.