Phasic stabilization of motor output after auditory and visual distractors

Area of Science:

• Neuroscience
• Motor Control
• Sensory Processing

Background:

• Maintaining steady motor output requires blocking distracting sensory stimuli.
• The primary motor cortex (M1) plays a crucial role in voluntary movement and motor control.
• Corticomuscular coherence (CMC) reflects the functional coupling between the motor cortex and muscles.

Purpose of the Study:

• To investigate the effects of brief auditory and visual distractors on the human primary motor cortex (M1).
• To examine how these distractors influence cortical rhythms, electromyogram (EMG) activity, and corticomuscular coherence (CMC).
• To understand the neural mechanisms underlying motor output stability when faced with sensory distractions.

Main Methods:

• Magnetoencephalography (MEG) was used to monitor cortical rhythms in M1.
• Electromyogram (EMG) of finger flexors was recorded during a right-hand pinch task.
• Auditory (1-kHz tones) and visual (checkerboard patterns) distractors were presented while measuring corticomuscular coherence (CMC).

Main Results:

• Both auditory and visual distractors induced covert startle-like responses, affecting force and EMG without visible movement.
• CMC and the rolandic ∼20-Hz rhythm were significantly enhanced for approximately 1 second following distractors.
• Directional coupling from muscle to M1 (EMG→MEG) increased after auditory distractors, suggesting startle-related proprioceptive input.

Conclusions:

• Task-unrelated distractors modulate corticospinal coupling at approximately 20 Hz.
• Distractors trigger covert startle responses and proprioceptive afference, leading to adjustments in corticospinal output to maintain motor task stability.
• Transient disengagement of attention from the fine-motor task likely contributes to the observed motor output readjustment.