The relationship of single unit activity to limb movements guided by visuospatial cues supports the view that the premotor cortex is a distinct cortical field within the somatic sensorimotor cortex. The premotor cortex is similar to the precentral motor cortex (MI) in that most of its units are clearly related to voluntary movements but differs from MI by its higher threshold for microstimulation-evoked movements, its cytoarchitecture, and the presence of a larger population of neurons with

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... vity related to the occurrence of visuospatial signals rather than, or in addition to, the movement cued by those signals. 1329