Brain areas involved in interlimb coordination: A distributed network

Whereas behavioral studies have made significant contributions toward the i dentification of the principles governing the coordination of limb movement s, little is known about the role of higher brain areas that are involved i n interlimb coordination. Functional magnetic resonance imaging (fMRI) was used to reveal the brain areas activated during the cyclical coordination o f ipsilateral wrist and foot movements. Six normal subjects performed five different tasks that were presented in a random order, i.e., isolated flexi on-extension movements of the right wrist (WRIST) and right foot (FOOT), cy clical coordination of wrist and foot according to the isodirectional (ISOD IR) and nonisodirectional (NON-ISODIR) mode, and rest (REST). All movements were auditory paced at 66 beats/min. During the coordination of both limb segments, a distributed network was identified showing activation levels in the supplementary motor area (SMA), cingulate motor cortex (CMC), premotor cortex (PMC), primary sensorimotor cortex (M1/S1), and cerebellum that exc eeded the sum of the activations observed during the isolated limb movement s. In addition, coordination of the limb movements in different directions was associated with extra activation of the SMA as compared to movements in the same direction. It is therefore concluded that the SMA is substantiall y involved in the coordination of the nonhomologous limbs as part of a dist ributed motor network. Accordingly, the long-standing exclusive association that has been made between this medial frontal area and bimanual (homologo us) coordination needs to be abandoned and extended towards other forms of interlimb coordination (nonhomologous). (C) 2001 Academic Press.