Dysmetria of thought: clinical consequences of cerebellar dysfunction on cognition and affect.

Cognitive and emotional changes might be prominent or even principal manifestations of cerebellar lesions. This realization supports evidence suggesting that the cerebellum is an important part of a set of distributed neural circuits that subserve higher-order processing. Early anecdotal clinical accounts described aberrant mental or intellectual functions in the setting of cerebellar atrophy. Later systematic analyses showed that the cerebellum is able to influence autonomic, vasomotor, and emotional behaviors, and further studies revealed neuropsychological deficits in patients with degenerative diseases. Current descriptions of behavioral changes in adults and children with acquired cerebellar lesions bring the debate about the cerebellar role in neural function within the realm of clinically relevant cognitive neuroscience. The activation of focal cerebellar regions by cognitive tasks on functional neuroimaging studies, and morphologic abnormalities of cerebellum in psychiatric diseases such as autism and schizophrenia further support this view. Anatomical substrates have been elucidated that could support a cerebellar role in cognition and emotion. Our concept of `dysmetria of thought' draws an analogy with the motor system to describe and explain the impairments of higher-order behavior that result when the distributed neural circuits subserving cognitive operations are deprived of cerebellar modulation.