By Anil Ananthaswamy DON’T blame impulsive people for their poor decisions. It’s not necessarily their fault. Being impulsive could be the result of 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 wanted to test whether we have free will. He asked participants were asked to sporadically flex a finger while watching a dot rotate round a clock-face. They had to note the position of the dot as soon as they became aware of their intention to act, while their brain activity was being recorded. Libet 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 move their finger. The readiness potential is thought to signal the brain preparing for movement. Libet interpreted his results to mean that free will is an illusion – if the action is initiated at a subconscious level and we only become conscious of our intention afterwards, how can we be initiating the action? But we’re not complete slaves to our neurons, he reasoned, as a 200-millisecond gap exists between conscious awareness of our intention and making a move. Libet argued that this was enough time to consciously veto the action, or exert our “free won’t”. While Libet’s interpretations remain controversial, this hasn’t stopped variations of his experiment. Among other things, researchers have discovered that people with schizophrenia and those with Tourette’s syndrome, who have uncontrollable tics, have a shorter veto window than people without those conditions. Impulsive people have less time to consciously veto their actions, or exert their ‘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 for impulsive people. They asked 72 people to fill in questionnaires to determine how impulsive they were. The participants took part in a Libet-style experiment while the researchers recorded their brain activity. The more impulsive the people were deemed to be, the shorter the interval between their awareness of the intention to act and the moment of action (Neuroscience of Consciousness, doi.org/bbsg). “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, cautions that any conclusions depend on how you interpret the various signals. His work suggests that the readiness potential is not a signal of the brain getting ready to act, but a signature of random neural noise that eventually crosses a threshold, making movement possible. But many neuroscientists still favour Libet’s interpretation of the readiness potential. If you accept this, Schurger says the study suggests that impulsive people have less time to “veto” their actions since the decision to act is much closer in time to the action itself. “The findings might point towards new avenues of research in the study of impulsivity, and related syndromes like bipolar disorder,” he says. (Image: Pixdeluxe/Getty) This article appeared in print under the headline “Impulsive?