The neurology of decreased activity: abulia.

Delirium is sometimes defined as acute onset of either overactivity or underactivity. This article reviews the nature and clinico-anatomical locations of lesions in patients with reduced activity. The term abulia is used to describe global underactivity. Abulia is customarily explained by interruptions in frontal-subcortical circuitry. These interruptions can occur with lesions in the frontal lobes, caudate nuclei, midbrain, and thalamus. The article describes the anatomy of frontal and subcortical circuits and reviews in detail individual cases and series of patients with reduced initiative and activity who have had localized central nervous system lesions.