ABSTRACT
Hallucinations are sensory images "seen" in the absence of external stimuli. They occur on falling asleep or waking up, during hypoglycemia, delirium, epilepsy, psychotic episodes, advanced syphilis, sensory deprivation, and migraine. Visual hallucinations appear to be stabilized against eye movements, in much the same way that external images are stabilized. This suggests that they are centrally, rather than peripherally located. If visual hallucinations are centrally located somewhere in the brain, it is appropriate to ask what is their geometry in terms of the coordinates of primary visual cortex or area. It is evident that visual hallucinations result from the Rayleigh-Benard-Turing instability, induced somewhere in the visual brain by the action of hallucinogenic drugs. Since each hypercolumnar region represents a visually distinct local patch of the visual field, the circuit may play a fundamental role in the analysis of visual images.
