Related Experiment Video
Updated: Aug 12, 2026
09:27
An Emerging Target Paradigm to Evoke Fast Visuomotor Responses on Human Upper Limb Muscles
Published on: August 25, 2020
Readiness potentials preceding spontaneous motor acts: voluntary vs. involuntary control
1Institute for Medical Psychology, University of Munich, F.R.G.
Electroencephalography and Clinical Neurophysiology
|October 1, 1990
Summary
Researchers explored the unconscious origins of voluntary movement. They found readiness potentials (RPs) precede both conscious and unconscious actions, suggesting focused attention may bring unconscious processes to awareness.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Motor Control
Background:
- Libet et al. (1983) proposed that cerebral initiation of spontaneous voluntary acts begins unconsciously, with conscious intention following readiness potential (RP) onset by 350 msec.
- This study investigates the alternative interpretation that heightened attention to internal states might make normally unconscious motor processes consciously detectable.
Purpose of the Study:
- To compare readiness potentials (RPs) during unconsciously performed movements, Libet's original paradigm, and introspective awareness of movement intention.
- To determine if RPs associated with spontaneous voluntary acts differ from those of unconscious movements.
- To explore the role of focused attention in the conscious awareness of motor initiation.
Main Methods:
- Three experiments were conducted: measuring RPs during unconscious movements, replicating Libet's study, and a resting condition with introspective focus on movement intentions.
- Electroencephalography (EEG) was used to record RPs, and scalp distributions were analyzed.
- Subjects' subjective experience of intention to move was recorded.
Main Results:
- Readiness potentials (RPs) preceding movement onset by approximately 500 msec were observed in both unconsciously and consciously performed spontaneous motor acts.
- Distinct scalp distributions indicated that unconscious movements involve contralateral processes (lateral premotor system, primary motor cortex), while voluntary acts are dominated by the medial premotor system (supplementary motor area).
Conclusions:
- The findings suggest that focused attention on internal events can lead to the conscious detection of normally unconscious processes.
- The medial premotor system, particularly the supplementary motor area (SMA), is implicated in voluntary spontaneous motor acts, with its activation potentially coinciding with the subjective urge to move.
- This challenges the strict interpretation of unconscious initiation for all voluntary actions, proposing a role for conscious awareness in detecting pre-initiated motor commands.
Related Concept Videos
01:15Muscle Contraction
01:10Muscle Contraction
In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate—the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle...
01:20Motor Unit Stimulation
When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
01:18Functions of the Nervous System
The nervous system is responsible for coordinating and regulating the body's functions. It functions through three main processes: sensory, integrative, and motor processes. Sensory function involves the detection and transmission of information about internal and external stimuli from sensory receptors to the CNS. The CNS processes this information through an integrative function, where it interprets and makes decisions based on the incoming sensory information. Finally, the motor function...
01:18Hierarchy of Motor Control
The hierarchy of motor control refers to the different levels of organization and processing involved in controlling movement in the body. These levels range from higher cortical areas involved in planning and decision-making to lower spinal cord reflexes that respond automatically to external stimuli.
01:11Direct Motor Pathways
The direct motor pathways, also known as the pyramidal tracts, are a group of neural pathways that originate in the brain and descend through the spinal cord. They control the voluntary movement of the body. There are two major direct motor pathways: the corticospinal and the corticobulbar tracts.
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the...
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the...