Abstract
Objectives: First, to measure the contraction force and to correlate these contraction force measures with the motor-evoked potentials (MEP) resulting from TMS, TST, Quadruple and Quintuple stimulation associated with the paired-pulse paradigm of SICI and ICF. Then, to compare the neuromuscular and electrophysiological responses between two groups of subjects according to their current and past physical activity.
Background: Transcranial magnetic stimulation (TMS) causes brain activation which generates repetitive spinal motor neuron discharges (RepMNDs). A paradigm called paired-pulse TMS (PP-TMS) allows inhibit or facilitate the neuromuscular response depending on the inter-stimulus interval (ISI) and the intensity of the two stimuli. The paired-pulse paradigm consists on the combination of a subthreshold conditioning stimulus (CS) preceding a suprathreshold test stimulus (TS) at different intervals. The triple stimulation technique (TST), the Quadruple stimulation (QuadS) and the Quintuple stimulation (QuintS) allow a more precise exploration of the motor conduction and of the RepMND.
Method: Investigation of 17 healthy volunteers in a randomized design study using single pulse and the paired-pulse paradigm of short intracortical inhibition (SICI) with an ISI of 2ms and an intracortical facilitation (ICF) with an ISI of 10ms through TMS, TST, QuadS and QuintS. Measurement of the contraction force of the abduction of the fifth digit corresponding of the Abductor Digiti Minimi muscle (ADM) using a force transducer.
Results: Negative correlation between the physical activity and the amplitude of the contraction force responses for all the stimulation techniques. Paradoxical positive correlation between the physical activity and the amplitude of the MEP response especially concerning QuadS and QuintS. Another founding is that about half of the subjects have repMNDs following a single pulse TMS in the QuadS and QuintS condition (60% and 40% respectively).
Conclusions: There is an inverse and paradoxical correlation between the contraction force responses and the MEP responses according to the physical activity of the subjects. These results point to potential association between MEP and the contraction force responses. Force contraction response may depend on the physical activity of each volunteer.