Don’t blame impulsive people for their poor decisions. It’s not necessarily their fault. Impulsivity could result from not having enough time to veto our own actions. At least that is the implication of a twist on a classic experiment on free will.

In 1983, neuroscientist Benjamin Libet performed an experiment to test whether we have free will. Participants were asked to voluntarily flex a finger while watching a clock-face with a rotating dot. They had to note the position of the dot as soon as they became aware of their intention to act. As they were doing so, Libet recorded their brain activity via EEG electrodes attached to the scalp.

He found that a spike in brain activity called the readiness potential, which precedes a voluntary action, occurred about 350-milliseconds before the volunteers became consciously aware of their intention to act. The readiness potential is thought to signal the brain preparing for movement.


Libet interpreted his results to mean that free will is an illusion. But we’re not complete slaves to our neurons, he reasoned, as there was a 200-millisecond gap between conscious awareness of our intention and the initiation of movement. Libet argued that this was enough time to consciously veto the action, or exert our “free won’t”.

While Libet’s interpretations have remained controversial, this hasn’t stopped scientists carrying out variations of his experiment. Among other things, this has revealed that people with Tourette’s syndrome, who have uncontrollable tics, experience a shorter veto window than people without the condition, as do those with schizophrenia.

Lack of ‘free won’t’

Emilie Caspar and Axel Cleeremans of the Free University of Brussels (ULB) in Belgium decided to see if the same was true in impulsive, but otherwise healthy, people. They asked 72 volunteers to complete standard questionnaires to determine how impulsive they were. Then, the volunteers took part in a Libet-style experiment while the researchers recorded their EEG signals.

People who were deemed impulsive did indeed have shorter time intervals between their conscious awareness of the intention to act and the moment of action. The more impulsive they were, the shorter the interval.

“It might suggest that maybe impulsive individuals have less time to inhibit or control their actions,” says Caspar.

Aaron Schurger at the Swiss Federal Institute of Technology in Lausanne, who has worked on understanding the implications of the Libet experiment, cautions that any conclusions depend on how you interpret the various signals. His own work suggests that the readiness potential is not a signal of the brain getting ready to act, but rather a signature of random neural noise that accumulates and then crosses a threshold, making movement possible.

But many neuroscientists still favour Libet’s interpretation of the readiness potential. In that case, Schurger says that the study shows that “impulsive people have less time to ‘veto’ their actions since the decision to act happens much closer in time to the action itself”.

“Setting aside arguments about interpretation, the findings might point towards new avenues of research in the study of impulsivity, and related syndromes like bipolar disorder,” says Schurger.

Journal reference: Neuroscience of Consciousness, DOI: 10.1093/nc/niv009

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