Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

Abstract

This study examined modulation of corticospinal excitability during both actual and imagined movements. Seven young healthy subjects performed actual (3% to 50% maximal voluntary contraction) and imagined index finger force production, and rest. Individual responses to focal transcranial magnetic stimulation (TMS) in four fingers (index, middle, ring, and little) were recorded for all three tested conditions. The force increments at the threshold of activation were derived from regression analysis, representing the TMS-induced response at the threshold activation of the corticospinal pathways. The increment in the index finger during motor imagery was larger than that at rest, but smaller than that at the threshold of activation. On the other hand, the increment in the uninstructed (middle, ring and little), slave fingers during motor imagery was larger than that at rest, but not different from that at the threshold of activation. These contrasting results suggest that the degree of imagery-induced enhancement in corticospinal excitability was significantly less than what could be predicted for threshold levels from regression analysis, but only for the index finger, and not the adjacent slave fingers. It is concluded that corticospinal excitability for the explicitly instructed index finger is specifically enhanced at subthreshold levels during motor imagery.

EEG and neuronavigated single-pulse TMS in the study of the observation/execution matching system: Are both techniques measuring the same process?

“…This lack of relationship is found despite faithful replication of previous results using these techniques in similar paradigms; namely, a significant increase in MEP amplitude and a significant attenuation of mu rhythm during action observation, imagination and execution (Fadiga et al, 1995;Li, 2007;Muthukumaraswamy et al, 2004;Pfurtscheller et al, 2006). This finding is surprising given that both measures are though to reflect sensorimotor activity during motor matching processes.…”

New evidence of corticospinal network modulation induced by motor imagery

“…In static conditions, corticospinal (MEP) and cervico-medullary excitabilities (CMEP), but not Ia-alpha synapse excitability (H-reflex), were facilitated during MI, suggesting a subliminal activation of the corticospinal track, insufficient to recruit (Li et al 2004;Rozand et al 2014;Stinear and Byblow 2003a), suggests that MI represents an intermediate level of activation of cortical structures between rest and voluntary contraction (Li 2007). However, this sole motor response does not provide enough information to dissociate cortical from spinal activation.…”

Voluntary Breathing Influences Corticospinal Excitability of Nonrespiratory Finger Muscles

“…The method and procedures of application of TMS were the same as those reported in previous studies (Danion et al 2003;Li 2007;Li et al 2004bLi et al , 2009). Briefly, focal TMS was performed with a figure-of-eight-shaped stimulation coil (mean diameter of each wing 45 mm) connected to a magnetic stimulator, with the maximal magnetic field strength of 2.2 Tesla.…”

“…EMG signals from FDS, EDC, and ADM muscles, force, and airflow rate data were recorded. The methods for measuring of magnitude and latency of MEPs due to focal TMS were the same as previously described (Danion et al 2003;Li 2007;Li et al 2004b). Briefly, from the rectified, unfiltered EMG signal, the background EMG (EMG BG ) was defined as the mean EMG calculated from Ϫ100 ms to the moment of TMS application (t 0 ).…”