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Prepared movements are elicited early by startle
Anthony N Carlsen1, Romeo Chua, J Timothy Inglis
1University of British Columbia, Vancouver, Canada.
Journal of Motor Behavior
|July 21, 2004
Summary
A startling acoustic stimulus significantly shortened reaction time (RT) in an arm extension task. The involuntary startle response did not alter the kinematics or electromyography (EMG) of the intended voluntary movement.
Area of Science:
- Neuroscience
- Motor Control
- Human Movement Science
Background:
- A startle stimulus can evoke a rapid, involuntary motor response.
- Previous research suggests this response occurs at very short latencies, bypassing the cerebral cortex.
- The precise nature of the startle response in relation to voluntary movement preparation requires further investigation.
Purpose of the Study:
- To investigate the characteristics of the startle response during a voluntary motor task.
- To determine if a startle stimulus influences the latency and kinematics of a prepared voluntary movement.
- To confirm the independence of the startle response from the voluntary motor command.
Main Methods:
- A simple reaction time (RT) task involving arm extension movements to three target distances (20, 40, 60 degrees).
- An unpredictable, intense acoustic startle stimulus (124 dB) was introduced in some trials, replacing the imperative stimulus.
- Electromyographic (EMG) activity was recorded from sternocleidomastoid and orbicularis oculi muscles to verify the startle reflex, and kinematic data of the arm movements were collected.
Main Results:
- Participants exhibited significantly shorter response latencies when startled compared to non-startled trials.
- The kinematic variables (e.g., movement trajectory, velocity) of the voluntary arm extension were largely unchanged across all target distances during startle trials.
- EMG characteristics of the voluntary response remained unmodified, indicating the execution of the prepared movement.
Conclusions:
- The startle stimulus accelerates the execution of a prepared voluntary motor response without altering its fundamental characteristics.
- The findings support the concept of a subcortical pathway mediating the startle response, which can interact with voluntary motor preparation.
- This study elucidates the neural mechanisms underlying the interplay between involuntary startle reflexes and voluntary motor control.