Abstract
BackgroundA peripheral nerve stimulus can enhance or suppress the evoked response to transcranial magnetic stimulation (TMS) depending on the latency of the preceding peripheral nerve stimulation (PNS) pulse. Similarly, somatosensory afference from the passively moving limb can transiently alter corticomotor excitability, in a phase-dependent manner. The repeated association of PNS with TMS is known to modulate corticomotor excitability; however, it is unknown whether repeated passive-movement associative stimulation (MAS) has similar effects.MethodsIn a proof-of-principle study, using a cross-over design, seven healthy subjects received in separate sessions: (1) TMS (120% of the resting motor threshold-RMT, optimal site for Flexor Carpi Radialis) with muscle at rest; (2) TMS paired with cyclic passive movement during extension cyclic passive movement (400 pairs, 1 Hz), with the intervention order randomly assigned. Normality was tested using the Kolmogorov-Smirnov test, then compared to pre-intervention baseline using repeated measures ANOVA with a Dunnet multiple comparisons test.ResultsMAS led to a progressive and significant decrease in the motor evoked potential (MEP) amplitude over the intervention (R2 = 0.6665, P < 0.0001), which was not evident with TMS alone (R2 = 0.0068, P = 0.641). Post-intervention excitability reduction, only present with MAS intervention, remained for 20min (0-10min = 68.2 ± 4.9%, P < 0.05; 10-20min = 73.3 ± 9.7%, P < 0.05).ConclusionThe association of somatosensory afference from the moving limb with TMS over primary motor cortex in healthy subjects can be used to modulate corticomotor excitability, and may have therapeutic implications.
Highlights
A peripheral nerve stimulus can enhance or suppress the evoked response to transcranial magnetic stimulation (TMS) depending on the latency of the preceding peripheral nerve stimulation (PNS) pulse
A single transcutaneous electrical peripheral nerve stimulus (PNS) generates an afferent volley that can modify the excitability of sensorimotor cortex as assessed by a change in somatosensory evoked potential (SSEP) amplitude following the PNS [1], or motor evoked potential (MEP) amplitude following transcranial magnetic stimulation (TMS) [2], increasing or decreasing excitability according to latency of
Based on the following factors, we propose that phase-specific cyclic passive movement when coupled with TMS repeatedly, may lead to a progressive modulatory effect: (1) the response to TMS depends on the state of the motor cortex at the time of stimulation [9], (2) that movement-generated afference can alter corticospinal output [3], (3) that consistent association of specific cortical afferent and efferent activity can modulate cortical excitability in animals [10] and humans [7,11]
Summary
A peripheral nerve stimulus can enhance or suppress the evoked response to transcranial magnetic stimulation (TMS) depending on the latency of the preceding peripheral nerve stimulation (PNS) pulse. A single transcutaneous electrical peripheral nerve stimulus (PNS) generates an afferent volley that can modify the excitability of sensorimotor cortex as assessed by a change in somatosensory evoked potential (SSEP) amplitude following the PNS [1], or motor evoked potential (MEP) amplitude following transcranial magnetic stimulation (TMS) [2], increasing or decreasing excitability according to latency of when coupled with TMS repeatedly, may lead to a progressive modulatory effect: (1) the response to TMS depends on the state of the motor cortex at the time of stimulation [9], (2) that movement-generated afference can alter corticospinal output [3], (3) that consistent association of specific cortical afferent and efferent activity can modulate cortical excitability in animals [10] and humans [7,11]. The aim of the present study was to investigate the effects of the TMS delivered during the inhibitory phase of cyclic passive movement on MEP amplitude
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