Intrinsic synaptic connectivity and basic mode of operation of the motor cortex

The nature of the motor cortex’s intrinsic synaptic connectivity is first considered. There are two principal views on this issue. One posits that connections between cortical points are patchy, tending to link non-contiguous points of similar representation. The other posits that the nature of the connectivity is such that it binds together a variety of contiguous muscle representations acting at the same, or different, joints. The evidence for each proposition is critically examined. On the basis of methodological shortcomings and physiological considerations of the studies supporting the patchy nature of connectivity, it is concluded that the nature of the connectivity is such that it binds together heterogeneous muscle representations contiguously. It should be clear, however, that both views strongly support the idea that the motor cortex’s intrinsic synaptic connectivity is integrative in nature and that it may be the neural basis of movement-related muscle synergies. However, there is as yet no experimental evidence that supports this idea. The mechanisms of function of the motor cortex are considered next. Evidence is provided to show that single motor cortex points do not contain the circuitry necessary to produce controlled natural movements. A coordinated selection of motor cortical points is required to produce a controlled natural movement trajectory.