Task-dependent modulation of inhibitory actions within the primary motor cortex

Abstract

In 11 healthy subjects motor-evoked potentials (MEPs) and silent periods (SPs) were measured in the right first dorsal interosseus (FDI) and abductor pollicis brevis muscles (APB): (1) when transcranial magnetic cortex stimulation (TMS) was applied at tonic isometric contraction of 20% of maximum force, (2) when TMS was applied during tactile exploration of a small object in the hand, (3) when TMS was applied during visually guided goal-directed isometric ramp and hold finger flexion movements, and (4) when at tonic isometric contraction peripheral electrical stimulation (PES) of the median nerve was delivered at various intervals between PES and TMS. Of the natural motor tasks, duration of SPs of small hand muscles was longest during tactile exploration (APB 205+/-42 ms; FDI 213+/-47 ms). SP duration at tonic isometric contraction amounted to 172+/-35 ms in APB and 178+/-31 ms in FDI, respectively. SP duration in FDI was shortest when elicited during visually guided isometric finger movements (159+/-15 ms). At tonic isometric contraction, SP was shortened when PES was applied at latencies -30 to +70 ms in conjunction with TMS. The latter effect was most pronounced when PES was applied 20 ms before TMS. PES-induced effects increased with increasing stimulation strength up to a saturation level which appeared at the transition to painful stimulation strengths. Both isolated stimulation of muscle afferents and of low-threshold cutaneous afferents shortened SP duration. However, PES of the contralateral median nerve had no effect on SPs. Amplitudes of MEPs did not change significantly in any condition. Inhibitory control of motor output circuitries seems to be distinctly modulated by peripheral somatosensory and visual afferent information. We conclude that somatosensory information has privileged access to inhibitory interneuronal circuits within the primary motor cortex.

Transcranial Magnetic Stimulation over Sensorimotor Cortex Disrupts Anticipatory Reflex Gain Modulation for Skilled Action

“…From a functional viewpoint, we suggest that these interneuronal networks may preparatorily adjusting reflex gains according to task demands. This modulation of reflexes may be basically similar to the known modification of such circuits during voluntary movements (Mathis et al, 1998(Mathis et al, , 1999Hess et al, 1999;Tinazzi et al, 2003).…”

“…Studies of voluntary movement show that interneuronal networks within M1 are modulated in a task-dependent manner (Mathis et al, 1998(Mathis et al, , 1999Hess et al, 1999;Tinazzi et al, 2003). For example, the duration of a long-lasting electromyogram (EMG) suppression [silent period (SP)] caused by transcranial magnetic stimulation (TMS) was longer during simple than complex manual tasks (Tinazzi et al, 2003) and during exploratory than visually guided movement .…”

Late cortical disinhibition in relaxed versus active hand muscles

“…During index abduction, many proprioceptive endings are stimulated and may then modulate corticospinal excitability. A large body of literature data suggests that information from skin and muscle afferents can interact with inhibitory networks in the primary motor cortex and thus modify motor output (Hess et al, 1999;Ridding and Rothwell, 1999;Rosenkranz and Rothwell, 2004). Although speculative, our hypothesis is supported by the finding that median nerve stimulation may decrease the intensity of LICI (Sailer et al, 2002;Udupa et al, 2009) and that in half of the subjects with LICI and long-latency afferent inhibition, LICI turned into facilitation when paired with peripheral median nerve stimulation (Sailer et al, 2002).…”

Efficacy of a Target-Matching Foot-Stepping Exercise on Proprioception and Function in Patients With Knee Osteoarthritis

“…We believed that the improvement in reposition error resulted from extensive practice, visual-motor transformation, and feedback processing. 9,12,13,34,35 The 6-week TMFSE intervention consisted of practicing both spatial (joint angle and movement extent) and temporal (pace) movement parameters. To complete the TMFSE, participants with knee OA actually practiced a great amount (about 1500 repetitions for each of 18 practice sessions, for a total of 27 000 repetitions) of visual-motor transformation and parameter specification.…”