Cortical involvement in the initiation of movements cued by moderate, but not loud acoustic stimuli: Evidence for subcortical mediation of the StartReact effect.

OBJECTIVE

The reticulospinal tract is critical for motor control, yet its role in human movement regulation remains incompletely understood. The StartReact effect is the primary method to assess reticulospinal motor control, although its neural mechanisms are debated. This study investigated the contribution of the motor cortex to the StartReact effect.

METHODS

The StartReact paradigm was administered to 22 healthy participants performing wrist extension movements to imperative stimuli (IS) consisting of either loud acoustic stimuli (LAS) or moderate acoustic stimuli (MAS). EMG and high-density EEG assessed muscle and cortical activity.

RESULTS

Reaction times were faster following LAS compared to MAS, reflecting the StartReact effect. Whereas movement-related cortical potentials emerged 21 ms before muscle activation following MAS, they appeared only 65 ms after muscle activation in LAS trials. Assessment of contingent negative variation (CNV) and event-related desynchronization (ERD) revealed no significant preparatory motor cortex activity prior to the IS.

CONCLUSIONS

These findings suggest that while the motor cortex plays a crucial role in mediating MAS-induced movements, it is not critically involved in initiating accelerated movements induced by LAS.

SIGNIFICANCE: Our results suggest that the StartReact effect is a subcortical phenomenon that primarily assesses reticulospinal motor control.