Visual hallucinations in blindness
Sep. 12, 2021
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Alexander and colleagues originally described a series of 5 parallel circuits that link particular regions of the frontal cortex to subcortical structures (Alexander et al 1990). The motor circuit originates primarily from the supplementary motor cortex and projects to the putamen in a somatotopic distribution. The oculomotor circuit arises in the frontal eye fields and connects to the central region of the caudate. The dorsolateral prefrontal circuit links Brodmann areas 9 and 10 with the dorsolateral head of the caudate. The lateral orbitofrontal circuit originates in the inferolateral prefrontal cortex and projects to the ventromedial caudate. The anterior cingulate circuit arises in the anterior cingulate gyrus and projects to the ventral striatum. This region also receives input from the amygdala, hippocampus, and entorhinal cortex. The motor and oculomotor circuits are potential sites for generation of tics. The dorsolateral prefrontal circuit appears to be involved with executive function and motor planning. Dysfunction of this pathway is postulated to lead to attentional and verbal impairments. Orbitofrontal injury is known to be associated with obsessive-compulsive disorder, personality changes, disinhibition, irritability, and mania. Lesions involving the anterior cingulate circuit result in mutism, apathy, and obsessive-compulsive disorder. (Adapted from: Singer HS, Minzer K. Neurobiology of Tourette’s syndrome: concepts of neuroanatomic localization and neurochemical abnormalities. Brain Dev 2003;25 (Suppl1):S70-84.)