Figure 1. Summary of inter-regional influences on the primary motor cortex.

The currently described influences of other brain areas on the output of the primary motor cortex (M1) are shown. Open arrows denote facilitation, while filled arrows denote inhibition. In many cases the influence shown represents a net effect of several specific interactions, whose details are discussed in the relevant section of the text and are shown in subsequent figures. These influences include projections from motor areas in the ipsi- and contralateral hemispheres and the effects of afferent sensory input. PMd = dorsal premotor cortex; PMv = ventral premotor cortex; SMA = supplementary motor area; PPC = posterior parietal cortex; CBL = cerebellum; THAL = thalamus; PNS = peripheral nervous system.