How the Human Brain Knows Its Own Movements ^{CEFR B2}

People frequently perform daily tasks without conscious realization, such as driving to a destination without remembering the journey. In the late 19th century, psychologists William James and Wilhelm Wundt proposed contrasting theories regarding action awareness. James argued that awareness occurs after a movement through sensory feedback, whereas Wundt maintained that it begins beforehand during motor planning. For over 130 years, researchers lacked the technology to test which theory was correct.

A recent study published in PNAS Nexus by Yale University researchers Hal Blumenfeld and David S. Jin has finally resolved this long-standing debate. They monitored 67 participants who played a sliding block puzzle game while attempting to memorize background videos. By recording brain activity with electroencephalography (EEG), the researchers discovered that both historical theories were accurate.

Aware actions depend on two combined neural signals:

• A motor-planning signal called pre-movement positivity before the action takes place.
• A sensory signal called N140 that occurs immediately after the movement.

The study also revealed that fatigue and distraction cause pupil diameter to shrink, reducing overall awareness. Interestingly, the authors noted that executing routine actions automatically is a beneficial feature that allows daily tasks to run smoothly. These findings could eventually aid patients with conditions like Parkinson's disease, schizophrenia, or stroke, where action awareness is impaired.