Brain modules of hallucination: an analysis of multiple patients with brain lesions.

We systematically reviewed the localization of focal brain lesions that cause isolated hallucination in a single sensory modality. Case reports of post-lesion nonparoxysmal hallucination in 1 (and only 1) of 3 sensory modalities (i.e., visual, auditory, somatic) were reviewed, and the content of the qualitative descriptions was analyzed for each modality. The lesion is practically always located in the brain pathway of the sensory modality of the hallucination. There seem to exist localized sensory brain circuits that in healthy people diminish the intensity of internal sensory representation. After a lesion, hallucinosis seems to be caused also by compensatory overactivation of tissue in the nearby brain sensory pathway. This type of hallucination may indeed be termed a "release" form, whereby patients are aware of the hallucinatory nature of their experience, but not usually of "dream centres" as proposed by Lhermitte. Instead, we propose that it is dreaming that should be considered a special case of neural "release."