SEEING VISUAL HALLUCINATIONS WITH FUNCTIONAL MAGNETIC-RESONANCE-IMAGING

We have used blood oxygenation level dependent imaging with functional magnetic resonance imaging (fMRI) to investigate the visual cortex re sponse to photic stimulation during and in the absence of continuous v isual hallucinations. A patient with cortical Lewy body dementia who e xperienced persistent and vivid complex hallucinations underwent fMRI on and off treatment with risperidone. When he was not hallucinating, photic stimulation produced a normal bilateral activation in striate c ortex. During hallucinations, very limited activation in striate corte x could be induced. We interpret this result as indicating that at lea st part of the activity in the brain responsible for the experience of visual hallucinations is located in the primary visual cortex.