Interruption of motor programmes by electrical or magnetic brain stimulation in man

Area of Science:

• Neuroscience
• Motor Control
• Human Movement Science

Background:

• Voluntary movement is initiated by complex neural processes originating in the brain.
• Understanding the precise timing and neural pathways involved in movement initiation is crucial for neuroscience and rehabilitation.

Purpose of the Study:

• To investigate the causal role of the brain, specifically the motor cortex, in delaying voluntary movement.
• To differentiate the effects of direct brain stimulation from peripheral nerve stimulation on movement timing.

Main Methods:

• Subjects performed rapid wrist flexion/extension in response to auditory cues.
• Transcranial electrical or magnetic brain stimulation was applied after the cue but before movement onset.
• Electromyography (EMG) recorded muscle activity, and H-reflexes assessed spinal motoneuron excitability.

Main Results:

• Brain stimulation delayed voluntary movement onset by up to 150 ms without altering EMG patterns.
• Peripheral median nerve stimulation did not delay movement.
• H-reflexes remained inducible during the delay, indicating spinal pathways were accessible.

Conclusions:

• Scalp electrical or magnetic brain stimulation selectively inhibits neural pathways involved in movement initiation, likely within the motor cortex.
• This inhibition temporarily disrupts the command signals to muscles, causing a delay in voluntary movement.
• The findings support a model where specific neuronal populations in the brain are critical for the precise timing of voluntary actions.