Precision pinch force control via brain and spinal motor neuron excitability during motor imagery.

This study presents a novel approach for identifying neural substrates underlying the beneficial effects of motor imagery. For motor imagery, participants were instructed to imagine contraction of the left thenar muscle at 50% maximal voluntary contraction (MVC). The participants then performed isometric contractions of the thumb and index finger at 50% MVC as accurately as possible after motor imagery and without motor imagery. F-waves and oxygen-hemoglobin levels were examined with and without motor imagery relative to the resting condition. These data were analyzed using structural equation modeling. The degree of changes in the excitability of spinal motor neurons using F-waves during motor imagery may be modulated by inputs from the supplementary motor area. F-waves were analyzed with respect to persistence and the F-wave/maximum M-wave amplitude ratio. We found an association between precision pinch force control after motor imagery and spinal motor neuron excitability during motor imagery. The excitability of the supplementary motor area was not directly associated with precision pinch force control. However, spinal motor neuron excitability was adjusted by the supplementary motor area. Thus, the ability to perform precision pinch force control may be influenced by the supplementary motor area through the excitability of spinal motor neurons.