The Anatomy of Manual Dexterity: The New Connectivity of the Primate Sensorimotor Thalamus and Cerebral Cortex

The macaque monkey uses the hand to grasp, digitally explore, and identify objects within reach, and to use them intelligently. This review is focused on the topography and connections of some of the neuron populations that determine this manual dexterity. Corticospinal, thalamocortical, and ipsilateral corticocortical neuron populations have been selected because of their obvious relevance to the use of the hand, and also because of their structural and functional interdependence. In the last decade these neuron populations have been analyzed using modern axon tracer techniques, single neuron recording in the alert monkey, and PET, resulting in a serious reconsideration of their structural and functional organization, and their roles in voluntary action. This review critically examines some of the new ideas triggered by these observations.