Startle decreases reaction time to active inhibition

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Reaction time (RT) tasks typically involve preplanned ballistic movements for rapid responses.
• Loud acoustic stimuli can elicit startle responses, involuntarily triggering movements at short latencies.
• It is hypothesized that startle provides activation to overcome motor initiation thresholds.

Purpose of the Study:

• To investigate if startle stimuli can shorten reaction times in tasks requiring motor inhibition (flexion force offset).
• To determine if the startle-induced effect on RT is specific to excitatory motor output or applicable to inhibitory tasks.
• To explore the neural mechanisms underlying startle-triggered inhibition.

Main Methods:

• Participants performed a simple reaction time task involving a flexion force offset (inhibition).
• A startling acoustic stimulus (SAS) was presented as the signal to inhibit motor output on specific trials.
• Electromyography (EMG) was used to measure muscle activity and command latencies.

Main Results:

• The inhibitory command was triggered significantly earlier by SAS (~78 ms latency) compared to voluntary control (~120 ms latency).
• Early, startle-related EMG activity was observed, superimposed with the triggered motor inhibition.
• This indicates that the inhibitory command involves active suppression of ongoing motor output.

Conclusions:

• Startling acoustic stimuli can trigger preprogrammed inhibitory motor commands earlier than voluntary control.
• This suggests that active inhibition, similar to excitation, can be rapidly initiated by startle.
• The findings imply that the nervous system actively suppresses motor output during startle-triggered inhibition.