The Effect of Motor Imagery on Spinal Segmental Excitability

Abstract

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 Ϯ 10.6 msec). This latency was similar to that recorded during a stretch of preactivated flexor muscles (34.4 Ϯ 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 Ϯ 3.7 msec), again similar to those induced by tendon taps (22.8 Ϯ 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.

Voluntary Breathing Influences Corticospinal Excitability of Nonrespiratory Finger Muscles

“…The range was consistent with a previous report (Yue et al 2000). The monosynaptic pathway (e.g., tendon reflex) for the finger flexors is about 24 ms (Li et al 2004a). It takes about 17 ms for the induced muscle force to peak as a consequence of electrical stimulation (Yue et al 2000).…”

The Spinal Substrate of the Suppression of Action during Action Observation

“…Studies aiming to evaluate the modulation of activity in the spinal cord during mental simulation provided conflicting results. Some researchers found no effect of mental simulation on the spinal cord (Abbruzzese et al, 1996; Yahagi et al, 1996;Kasai et al, 1997;Hashimoto and Rothwell, 1999;Facchini et al, 2002;Patuzzo et al, 2003), whereas others reported a modulation (Kiers et al, 1997;Rossini et al, 1999;Baldissera et al, 2001;Li et al, 2004;Borroni et al, 2005Montagna et al, 2005;. Indeed, the majority of the studies reporting spinal modulation during action-observation and motor-imagery concluded that the changes in the amplitude of the motor-evoked potentials are mainly due to excitability changes in the motor cortex (Kiers et al, 1997;Rossini et al, 1999;Borroni et al, 2005;Montagna et al, 2005;, whereas only one provided evidence for changes in the excitability of the spinal segmental circuitry, independent of the modulation of the motor cortex (Li et al, 2004).…”

Volition and Imagery in Neurorehabilitation

“…fMRI and TMS studies 23 demonstrated that cM1 is activated during imagery tasks of increasingly complex movements, a result consistent with a previous finding of more prominent involvement of M1 with performance of complex motor sequences. 24 Further evidence for the existence of common brain regions engaged in performance and imagination of movements comes from work by Li et al 25 These authors illustrated similarities in characteristics of finger interactions during both motor imagery and motor execution. Although motor performance and motor imagery activate similar neural networks, the psychologic setting in place clearly differs.…”