One fundamental function of primary motor cortex (MI) is to control volunta
ry movements. Recent evidence suggests that this role emerges from distribu
ted networks rather than discrete representations and that in adult mammals
these networks are capable of modification. Neuronal recordings and activa
tion patterns revealed with neuroimaging methods have shown considerable pl
asticity of MI representations and cell properties following pathological o
r traumatic changes and in relation to everyday experience, including motor
-skill learning and cognitive motor actions. The intrinsic horizontal neuro
nal connections in MI are a strong candidate substrate for map reorganizati
on: They interconnect large regions of MI, they show activity-dependent pla
sticity, and they modify in association with skill learning. These findings
suggest that MI cortex is not simply a static motor control structure. It
also contains a dynamic substrate that participates in motor learning and p
ossibly in cognitive events as well.