Representation of the hand in the cerebral cortex.

In this brief review, the body of work on hand use and cortical plasticity is reviewed. The hand movements and sensory inputs are represented in the mammalian primary motor cortex and the anterior parietal strip. The dominant organizational rules are that representational area is proportional to peripheral innervation, and that cortical architecture is columnar with limited horizontal spread. The representational area and columnar structure can be shaped by behavior and other input manipulations. The central core systems, and especially cholinergic inputs, act as teachers of the cerebral cortex by marking behavioral reinforcers with the release of acetylcholine. This marking is both necessary and sufficient for plasticity to occur in sensory cortex. As a result of this temporal marking of reinforcing events, nearly coincident inputs over restricted sensory, or motor, segments form coherent representations in primary sensory or motor cortex. Focal dystonia is a problem in which overuse of the hand leads to a lack of motor control, and especially inappropriate use of sensory feedback for motor control. Receptive field size, and columnar architecture, are highly abnormal in this disorder. The deficiencies in focal dystonia, and their appropriate treatment, can be understood by applying the principles of cortical plasticity to the behavioural manipulations that cause focal dystonia.