Hallucinations

Hallucinations are involuntary sensory experiences that are perceived as emanating from the external environment, in the absence of stimulation of relevant sensory receptors. Hallucinations can occur in a variety of contexts but are perhaps most striking and debilitating in the context of schizophrenia, in which they are generally experienced as real and emotionally significant, are related to concurrent delusions, and represent a manifestation of psychosis. Hallucinations can occur in any sensory modality and can involve multiple modalities. Auditory hallucinations are the most common in schizophrenia and other illnesses that are traditionally termed psychiatric, and visual hallucinations are the most common in illnesses termed neurological. Hallucinations can be described at multiple levels of analysis, including cognitive, neurochemical, computational, and social/psychological. This article presents a functional neuroanatomic approach to hallucinations describing and analyzing them in terms of disorders of sensory input and subcortical (mindbrain/thalamus) and higher brain regions, including cortical sensory, limbic, and frontal regions. It touches also on treatment considerations.