Interlimb neural interactions in the corticospinal pathways

Abstract

Corticospinal excitability is known to be modulated during voluntary muscle contraction of distal limbs. Although a large number of studies have demonstrated the variety of modulations in corticospinal excitability during distal limb movement, those interlimb neural interactions in corticospinal excitability have not been fully understood. Here, we mainly review previous studies that used transcranial magnetic stimulation (TMS) to report the modulation of corticospinal excitability during distal limb movement, and discuss related neural mechanisms and functional implications. Corticospinal modulation, produced across the limbs, was observed regardless of the combination of limbs (i.e., upper limbs, upper and lower limbs, and lower limbs). The pattern of modulation depended on the strength and the modality of muscle contraction in the active limb. Discrete forceful isometric contraction tended to facilitate corticospinal excitability in the tested muscle of the opposite limb. However, isotonic muscle contraction tended to show suppression or movement phase-locked specific facilitation. In association with the involvement of modulation in spinal motoneuronal and intracortical motor circuitry, it was suggested that different neural mechanisms mediate each pattern of corticospinal modulation.

Keywords

• corticospinal tract
• primary motor cortex
• motoneuron
• transcranial magnetic stimulation
• voluntary muscle contraction