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The Journal of Neuroscience, October 27, 2004, 24(43):9674-9680; doi:10.1523/JNEUROSCI.2781-04.2004

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Behavioral/Systems/Cognitive
The Effect of Motor Imagery on Spinal Segmental Excitability

Sheng Li,¹ Derek G. Kamper,^2,3 Jennifer A. Stevens,⁴ and William Z. Rymer^2,3

¹Department of Physical Therapy, University of Montana, Missoula, Montana 59812, ²Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611-3008, ³Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois 60611-2654, and ⁴Department of Psychology, College of William and Mary, Williamsburg, Virginia 23187-8795

The purpose of this study was to investigate the effect of motor imagery on spinal segmental excitability by recording the reflex responses to externally applied stretch of the extrinsic finger flexors and extensors during the performance of an imaginary task. Nine young healthy subjects performed a series of imagined flexion-extension movements of the fingers. Muscle stretch was imposed concurrently by applying rotations of the metacarpophalangeal joints at 100, 300, or 500°/sec. Three of the nine tested subjects also generated 0.2 Newton meter voluntary flexion torque in preloading tasks before stretch.

At 300°/sec stretch, electromyogram (EMG) and torque reflex responses, which were observed in the finger flexors in four of nine subjects during motor imagery, were activated at a short latency (38.6 ± 10.6 msec). This latency was similar to that recorded during a stretch of preactivated flexor muscles (34.4 ± 3.6 msec), in which motoneurons are already suprathreshold and in which monosynaptic effects of muscle afferents are likely to be discernable. In a similar manner, for stretches imposed at 500°/sec, responses to stretch of the flexors were observed in all five tested subjects in imaginary flexion tasks at very short latencies (26.4 ± 3.7 msec), again similar to those induced by tendon taps (22.8 ± 1.2 msec). No EMG response was observed at rest during stretches.

These observations support the view that effects must have been mediated by imagery-related subthreshold activation of spinal motoneurons and/or interneurons, rather than by long-latency transcortical reflex responses. We conclude that motor imagery has a potent effect on the excitability of spinal reflex pathways.

Key words: motor imagery; stretch reflex; spinal excitability; motor; fingers; human

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Received July 12, 2004; revised September 12, 2004; accepted September 13, 2004.

This article has been cited by other articles:

				T. Hanakawa, M. A. Dimyan, and M. Hallett Motor Planning, Imagery, and Execution in the Distributed Motor Network: A Time-Course Study with Functional MRI Cereb Cortex, March 20, 2008; (2008) bhn036v1. [Abstract] [Full Text] [PDF]

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