|Title of the paper:||The corticospinal excitability increase after somatosensory stimulation at rest and during motor imagery is time interval-dependent|
|Authors:||Traverse, E., Lebon, F., Martin, A.|
|Institution:||INSERM Université Bourgogne Franche-Comté|
|Department:||Faculty sport science|
Saito et al., 2013 demonstrated that corticospinal excitability increased during motor imagery (MI) combined with somatosensory stimulation (SS) induced by electrical stimulation of the peripheral nerve. These modulations may involve peripheral and/or cortical processes, especially the primary motor cortex and primary somatosensory cortex, known to be activated during kinesthetic MI modality. The aim of the current study was to assess the interaction between SS and MI on CSE using different time-interval.
Six subjects performed the experiment. Transcranial magnetic stimulation (TMS) of the primary motor cortex was applied at an intensity of 120% of rest motor threshold to evoke an unconditioned motor evoked potential (MEP) at rest or during an imagined maximal plantar flexion of the right foot. SS was induced using a triplet electrical stimulation applied on the posterior tibial nerve at 80% of motor threshold at rest or during MI. To test the effect of afferences on CSE, TMS was applied 1 to 150ms after SS to evoke a conditioned MEP (MEPc) at rest and during MI. Peak-to-peak MEP and MEPc amplitudes were analyzed for the soleus muscle and expressed as function of the unconditioned MEP.
At rest, MEPc amplitude increased for the time intervals of 20 to 50ms (mean : +38 ± 24%) and from 100ms (+37.4 ± 29%). During MI, unconditioned MEP increased by +61.1 ± 13% in comparison to rest. MEPc amplitude was not modulated up to 100ms and increased at 150ms (+46.4 ± 22%). At 150 ms, MEPc increased during MI and rest was similar.
At rest, CSE increased when the stimulation was induced at least 20ms after the SS. This latency allows the somatosensory volley to reach the cortical level (Carson & Kennedy, 2013), specifically the primary somatosensory cortex that modulates the primary motor cortex activity (Veldman et al., 2015). During MI, SS did not further increase CSE. This lack of modulation could be possibly due to a conflict that arises at the primary motor cortex level between neural activities induced by MI and those induced by SS. Beyond 100ms, the cortical network possibly returns to its basic state and so the CSE similarly increased at rest and during MI combined with SS.
|Topic:||Motor Learning and Motor control|
|Keyword I:||corticospinal excitability|
|Keyword II:||Transcranial magnetic stimulation (TMS)|
|Keyword III:||motor imagery|