How the Brain Controls Awareness of Our Actions

A study published in PNAS Nexus has identified that consciousness of one’s own actions depends on a combination of motor-planning and sensory-processing brain signals. Led by Hal Blumenfeld, a professor of neurology at Yale School of Medicine, and David S. Jin, the research suggests that awareness is not triggered by a single signal but by multiple cognitive domains working in tandem.

The findings resolve a 130-year-old academic conflict between psychologists William James and Wilhelm Wundt. James argued that awareness of action occurs after a movement through sensory feedback, while Wundt claimed it arises from the brain’s act of planning and initiating movement before sensation occurs. According to Blumenfeld, the new data indicates that James and Wundt were both right, as both volition- and perception-related signals increase when a person is aware of their actions.

How Brain Signals Determine Action Awareness

Researchers utilized electroencephalography (EEG) to monitor the brain activity of 67 participants. To test awareness, Jin designed a task using a version of the Rush Hour sliding block puzzle. Participants played the game while simultaneously attempting to memorize background videos. At random intervals, the game paused, and participants were asked to identify their last move and rate their confidence in that answer.

The study categorized moves as aware when participants provided correct answers with high confidence. Moves were labeled unaware when answers were incorrect and confidence was low. The EEG data revealed two distinct signals that differed between these two states:

• Pre-movement positivity: A motor-planning signal that was stronger during aware trials.
• N140: A sensory processing signal tied to the awareness of bodily sensation, which was also enhanced during aware trials.

The research team found that neither signal alone was sufficient to produce awareness; both were required to determine if a person was conscious of their movement.

The Impact of Alertness on Consciousness

The Yale study identified a third variable influencing awareness: physical alertness. As the sessions progressed, researchers observed that participants’ pupil diameters shrank. This shrinkage served as a proxy for dwindling alertness.

Blumenfeld stated that as participants became more bored, tired, or distracted, their pupils grew smaller and their awareness of their own actions declined in lockstep. He noted that this redundancy in signals—where multiple factors influence awareness—likely serves an evolutionary purpose because consciousness is so critical.

Clinical Relevance and Future Research

The researchers noted that unawareness may be a functional feature of the human brain. Jin suggested that constant awareness of every single action would be impractical, citing the example of a musician who must play notes without thinking through every individual movement moment by moment.

However, the disruption of these signals has significant clinical implications. According to the study, the same brain signals that were diminished in the unaware participants are also diminished in patients with Parkinson’s disease. Similar disruptions are observed in individuals with schizophrenia and those recovering from a stroke.

Blumenfeld stated that these disruptions can have real consequences for medical diagnosis, rehabilitation, and legal determinations regarding intent. Because previous research focused heavily on perceptual awareness, this study into action awareness expands the scope of the field.

The research team plans to move toward using functional magnetic resonance imaging (fMRI) in future steps. This technology will provide better spatial resolution to examine signals deep within the brain that surface EEG cannot reach.

The study was supported by the National Institutes of Health, Yale University, the Mark Loughridge and Michele Williams Foundation, and the Betsy and Jonathan Blattmachr Family.