Despite recent advances in functional neuroimaging, the apparently simple question of how and where we see—the neurobiology of visual consciousness—continues to challenge neuroscientists. Without a method to differentiate neural processing specific to consciousness from unconscious afferent sensory signals, the issue has been difficult to resolve experimentally. Here we use functional magnetic resonance imaging (fMRI) to study patients with the Charles Bonnet syndrome, for whom visual perception and sensory input have become dissociated. We found that hallucinations of color, faces, textures and objects correlate with cerebral activity in ventral extrastriate visual cortex, that the content of the hallucinations reflects the functional specializations of the region and that patients who hallucinate have increased ventral extrastriate activity, which persists between hallucinations.
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We are grateful to Kim Miller, the Buckinghamshire Association for the Blind, T. J. ffytche, D. McHugh and G. Plant for referring their patients and to the staff of the Neuroimaging group at the Institute of Psychiatry. D.H.ff. is a Wellcome Clinician Scientist Fellow.
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ffytche, D., Howard, R., Brammer, M. et al. The anatomy of conscious vision: an fMRI study of visual hallucinations . Nat Neurosci 1, 738–742 (1998). https://doi.org/10.1038/3738
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