SHARED NEURAL SUBSTRATES CONTROLLING HAND MOVEMENTS IN HUMAN MOTOR CORTEX

Voluntary hand movements in humans involve the primary motor cortex (M 1). A functional magnetic resonance imaging method that measures relat ive cerebral blood flow was used to identify a distributed, overlappin g pattern of hand movement representation within the posterior precent ral gyrus, which contains M1. The observed pattern resembles those rep orted in nonhuman primates and differs from a somatotopically organize d plan typically used to portray human motor cortex organization. Fing er and wrist movements activated a wide expanse of the posterior prece ntral gyrus, and representations for different finger movements overla pped each other and the wrist representation. Multiple sites of activa tion occurred in the precentral gyrus for all movements. The overlappi ng representations may mediate motor and cognitive functions requiring coordinated neural processing for finger and wrist actions rather tha n discrete control implied by somatotopic maps.