Unconscious Influences on "Free Will" Movement Initiation: Slow-wave Brain Stimulation and the Readiness Potential

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Motor Control

Background:

• The readiness potential (RP) in EEG is traditionally viewed as a neural marker for voluntary movement initiation.
• Alternative theories propose RPs may arise from ongoing brain oscillations influencing movement timing.
• Understanding the neural basis of volition and free will remains a central challenge.

Purpose of the Study:

• To investigate if slow-wave brain oscillations, modulated by transcranial alternating current stimulation (tACS), influence the timing of voluntary movement.
• To determine if external stimulation can alter premovement EEG signals like the readiness potential.

Main Methods:

• Participants (n=30) performed a self-paced button press task.
• Transcranial alternating current stimulation (tACS) was applied at a slow-wave frequency over frontocentral motor areas.
• Pre-movement EEG activity, including the readiness potential (RP), was recorded and analyzed during active tACS and sham conditions.

Main Results:

• Participants tended to initiate actions in sync with the tACS cycle phase associated with increased frontocentral negativity.
• Active tACS led to earlier onset and increased amplitude of RPs compared to sham stimulation.
• These findings suggest non-conscious modulation of movement-related brain activity by tACS.

Conclusions:

• The timing of voluntary movement initiation can be influenced by the phase of underlying slow-wave brain oscillations.
• External stimulation, like tACS, can modulate neural activity preceding self-paced movements.
• This supports theories linking brain oscillations to the temporal control of voluntary actions.