Motor Cortex

M1 has been identified in several mammals, but most information comes from monkeys, cats, raccoons, rats, and humans. In each, five characteristics serve to define M1: (1) electrical stimulation there evokes movements with relatively low levels of electrical current, usually less than needed in other cortical fields; (2) it lacks a clearly identifiable internal granular layer, layer 4, and therefore is part of the agranular frontal cortex; (3) it receives a major input from the ventrolateral thalamus, which relays information from the cerebellum and basal ganglia; (4) it lies rostral and medial to the somatosensory cortex; and (5) it sends direct projections to the spinal cord (Figure 1).