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Patterned ballistic movements triggered by a startle in healthy humans.
J Valls-Solé1, J C Rothwell, F Goulart
1Unitat d'EMG, Servei de Neurologia, Departament de Medicina, Hospital Clinic, Universitat de Barcelona, Barcelona, Spain. valls@medicina.ub.es
The Journal of Physiology
|April 14, 1999
Summary
An unexpected loud noise significantly speeds up reaction time to a visual cue by nearly half. This effect, observed in healthy subjects, suggests subcortical pathways, not just reflexes, initiate rapid voluntary movements.
Area of Science:
- Neuroscience
- Human Physiology
- Motor Control
Background:
- Reaction time to visual stimuli can be influenced by auditory cues.
- The central nervous system (CNS) integrates sensory information for motor responses.
- The startle reflex is a rapid, involuntary response to a sudden stimulus.
Purpose of the Study:
- To investigate the physiological mechanisms behind reaction time shortening due to acoustic startle.
- To determine if voluntary movement commands and startle reflexes interact at the CNS level.
- To explore the role of subcortical pathways in rapid voluntary actions.
Main Methods:
- Healthy volunteers performed voluntary wrist or leg movements upon a visual 'go' signal.
- Electromyography (EMG) patterns were recorded to analyze motor responses.
- A loud acoustic stimulus, capable of eliciting a startle reflex, was unexpectedly presented with the 'go' signal.
Main Results:
- Acoustic startle nearly halved voluntary response latency.
- EMG patterns of voluntary movements remained unchanged.
- Some reaction times were faster than theoretically possible for cortical processing.
- Participants reported responses felt involuntary.
Conclusions:
- Shortened reaction times are not due to additive startle and voluntary responses.
- Rapid reactions are likely triggered by subcortical structures, possibly involving the startle circuit.
- Voluntary movement instructions may be stored and released from subcortical levels.