Preparatory Suppression and Facilitation of Voluntary and Involuntary Responses to Loud Acoustic Stimuli in an Anticipatory Timing Task.

Abstract

In this study, we sought to characterise the effects of intense sensory stimulation at different stages of preparation for an anticipated action on voluntary and involuntary behaviours. In our experiment, we presented unexpected loud acoustic stimuli (LAS) at four critical times during movement preparation to probe the state of the nervous system (Baseline, -1192 ms, -392 ms, and 0 ms relative to expected movement onset), and measured their effect on voluntary and involuntary motor actions (finger-press and eye-blink startle reflex, respectively). Voluntary responses were largely facilitated by the LAS, leading to earlier and more forceful responses compared to Control and Baseline conditions. Notably, voluntary responses were significantly facilitated on trials where the LAS was presented early during preparation (-1192 ms). Eye-blink reflexes elicited by the LAS at -392 ms were significantly reduced and delayed compared to other time-points, indicating suppression of sub-cortical excitability. Despite being in a suppressive state, voluntary responses on these trials were still facilitated by the LAS. The results provide insight into the mechanisms involved in preparing anticipatory actions. Induced activation can persist in the nervous system and can modulate subsequent actions for a longer time period than previously thought, highlighting that movement preparation is a continuously evolving process that is susceptible to external influence throughout the preparation period. Suppression of sub-cortical excitability shortly before movement onset is consistent with previous work showing corticospinal suppression which may be a necessary step before the execution of any voluntary response.