Effects of a competitive stressor on motor cortex excitability: a pilot study

Several intervening variables may influence motor evoked potentials IM-EPI from transcranial magnetic stimulation (TMS). Among the most common are mot or (e.g. executed or intended muscle contraction) and sensory factors. Howe ver, little is known about the effects of a well defined stressor on MEPs a nd thus on central motor control. We studied 11 healthy right-handed volunt eers (five melt and six women), aged 21-32 years (mean 25.2 years, SD = 3.5 ). All subjects underwent a 20 min rest and a 20 mill stress period (sequen ce-controlled, cross-over design). The stressor employed a competitive vide ogame. MEPs from the left abductor digiti minimi muscle were obtained immed iately after rest and stress. We found that six (54.5 pei cent) subjects pr esented a significant increase (p < 0.05) of MEP amplitudes from rest to st ress, three (27.3 per cent; p < 0.05) decreased, and two (18.2 per cent) di d not change. F- and M-waves did not change significantly. Psychological te sting (state and trait anxiety inventory, STAI) revealed that individuals w ho presented an increase in MEP latency scored lower in state and trait anx iety than others, probably indicating a lower vulnerability to stress. We b elieve that the observed increase in MEP amplitudes, combined with a decrea se in MEP latency, call be regarded as neurophysiological evidence of stres s-induced facilitation related to higher excitability of the corticospinal system and/or presynaptic neurons. Copyright (C) 2000 John Wiley & Sons, Lt d.