Résumé
Cognitive fatigue is a commonly experienced psychobiological state characterized by a sense of mental exhaustion that emerges with prolonged cognitive effort. It has been shown to impair motor performance, including reaction time (RT). However, it remains unclear whether such effects are accompanied by changes in corticospinal excitability, particularly during the preparatory period preceding a rapid motor response. As such, this study used single-pulse transcranial magnetic stimulation (TMS) to probe corticospinal excitability during the foreperiod of a simple RT task. Participants (n=23) completed a 60-min cognitively fatiguing task (Math & Memory) and a control task (documentary viewing) on separate days. Pre- and post-intervention measures included subjective ratings of cognitive fatigue and premotor simple RT in a button-press task. Corticospinal excitability was assessed by recording motor-evoked potential (MEP) amplitude from the first dorsal interosseus muscle at 0, 150, and 500ms prior to the go-signal within the RT task, along with threshold TMS intensity to evaluate baseline excitability. As expected, subjective fatigue significantly increased following the cognitive fatigue task (p<.001). Contrary to prior findings, simple RT became faster following both interventions (p=.003). While no significant change was observed in threshold TMS intensity (p>.500), MEP amplitude diverged by condition: it decreased following the control task (p=.004) but increased following the cognitive fatigue task (p=.019). These findings suggest a compensatory neuromotor adaptation, wherein elevated corticospinal excitability during response preparation may help to preserve simple reaction time performance in the presence of increased cognitive fatigue.
