Hallucinations
“In the primary visual cortex, located in the occipital lobes, at the back of the brain, there are point-to-point mappings of the retina onto the cortex, and it is here that light, shape, orientation, and location in the visual field are represented. Impulses from the eyes take a circuitous route to the cerebral cortex, some of them crossing to the opposite side of the brain as they do so, so that the left half of the visual field of each eye goes to the right occipital cortex, and vice versa. I...f, therefore, one occipital lobe is damaged (as by a stroke, for example), there will be blindness or impaired vision in the opposite half of the visual field—a hemianopia.
Besides the impairment or loss of vision to one side, there may be positive symptoms, too—hallucinations in the blind or purblind area. About 10 percent of patients with sudden hemianopia get such hallucinations—and immediately recognize them to be hallucinations.
In contrast to the relatively brief and stereotyped hallucinations of migraine or epilepsy, the hallucinations of hemianopia may continue for days or weeks on end; and, far from being fixed or uniform in format, they tend to be ever changing.MoreLess
Besides the impairment or loss of vision to one side, there may be positive symptoms, too—hallucinations in the blind or purblind area. About 10 percent of patients with sudden hemianopia get such hallucinations—and immediately recognize them to be hallucinations.
In contrast to the relatively brief and stereotyped hallucinations of migraine or epilepsy, the hallucinations of hemianopia may continue for days or weeks on end; and, far from being fixed or uniform in format, they tend to be ever changing.MoreLess
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