Intrinsic synaptic organization of the motor cortex.

Recent anatomical and electrophysiological studies of the intrinsic synaptic circuitry of the motor cortex are revealing novel aspects related to the functional organization of this cortical area. These studies demonstrate that the motor cortex is composed of modules consisting of columnar aggregates of neurons related to different aspects of the same movement. Excitatory and inhibitory connections of intracortical origin link neurons within each of these cortical modules, and also mediate interactions between different cortical modules located as far as 2-3 mm from each other. The intrinsic excitatory connections utilize glutamate, and act via both NMDA and non-NMDA postsynaptic receptors. The intrinsic inhibitory connections are GABAergic. Intrinsic cortical circuits are involved in the temporal coordination of different cortical modules for the execution of complex movement patterns. In addition, the intrinsic inhibitory and excitatory connections are involved in the plasticity of representation zones in the motor cortex, a phenomenon that occurs following nerve damage or during the acquisition of novel motor skills.