Abstract
BackgroundShort-latency intracortical inhibition (SICI) and motor surround inhibition (mSI) are cortical phenomena that have been investigated with transcranial magnetic stimulation (TMS). mSI is believed to be necessary for the execution of fine finger movements, SICI may participate in mSI genesis, and however, the mechanisms underlying both mSI and SICI are not entirely clear.ObjectiveWe explored the cortical physiology of SICI and mSI in healthy subjects by TMS-evoked cortical potentials (TEPs).Methods:Single (sp) and paired-pulse (pp) TMS were delivered on the ADM muscle cortical hotspot while recording EEG and EMG. Three conditions were tested: spTMS and ppTMS at rest, and spTMS at the onset of an index finger movement. SICI and mSI were calculated on the ADM motor evoked potential (MEP) and two groups were defined based on the presence of mSI. Average TEPs were calculated for each condition and for five regions of interest.ResultsAt movement onset we observed a widespread reduction of the inhibitory late component N100 suggesting cortical facilitation associated with motor performance. At motor cortex level, SICI and mSI are associated with similar modulation of TEPs consisting in a reduction of P30 and an increase of N45 amplitude.ConclusionOur findings suggest that SICI and mSI modulate cortical excitability with shared inhibitory mechanisms.
Highlights
Short interval intracortical inhibition (SICI) can be investigated with transcranial magnetic stimulation (TMS) using paired-pulse paradigm where the motor evoked potential (MEP) produced by a test stimulus (TS) is reduced in amplitude if delivered 1–5 ms following a weak conditioning stimulus (CS) (Valls-Solé et al, 1992; Kujirai et al, 1993)
Because of motor Surround inhibition (SI), the MEP produced by a single pulse TMS in a surround muscle is reduced at the onset of a voluntary movement performed with a target/synergist muscle (Beck and Hallett, 2011). mSI should be helpful for the execution of fine finger movements and is thought to be the result of selective facilitation of muscles synergistic to the movement and inhibition of competitive ones (Hallett, 2003)
In the present study on healthy subjects we investigated the effect of SICI, movement onset and mSI on the TMS-evoked cortical potential (TEP) produced by M1 stimulation
Summary
Short interval intracortical inhibition (SICI) can be investigated with transcranial magnetic stimulation (TMS) using paired-pulse paradigm where the motor evoked potential (MEP) produced by a test stimulus (TS) is reduced in amplitude if delivered 1–5 ms following a weak conditioning stimulus (CS) (Valls-Solé et al, 1992; Kujirai et al, 1993). Because of motor SI (mSI), the MEP produced by a single pulse TMS (spTMS) in a surround muscle is reduced at the onset of a voluntary movement performed with a target/synergist muscle (Beck and Hallett, 2011). MSI should be helpful for the execution of fine finger movements and is thought to be the result of selective facilitation of muscles synergistic to the movement and inhibition of competitive ones (Hallett, 2003). Short-latency intracortical inhibition (SICI) and motor surround inhibition (mSI) are cortical phenomena that have been investigated with transcranial magnetic stimulation (TMS). Short-latency intracortical inhibition (SICI) and motor surround inhibition (mSI) are cortical phenomena that have been investigated with transcranial magnetic stimulation (TMS). mSI is believed to be necessary for the execution of fine finger movements, SICI may participate in mSI genesis, and the mechanisms underlying both mSI and SICI are not entirely clear
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