The neural basis of Charles Bonnet hallucinations: a hypothesis.

OBJECTIVES To describe the hallucinations occurring as a result of a macular hole in each eye and to investigate the neural basis. METHODS Psychophysical observations including sketches of the hallucinations calibrated for size. RESULTS All the hallucinations were of the geometric (patterned) type and lasted for only a few days. CONCLUSIONS The observations can be explained on the basis of a "deafferentation" model, which is described in some detail. It is proposed that the hallucinations result from activation of the "blobs" of area V1 and the "stripes" of area V2 in the visual cortex. A theory is proposed to account for the disappearance of the hallucinations by a "filling in" mechanism.