Back in the 1980s, the American scientist Benjamin Libet made a surprising discovery that appeared to rock the foundations of what it means to be human. He recorded people’s brain waves as they made spontaneous finger movements while looking at a clock, with the participants telling researchers the time at which they decided to waggle their fingers. Libet’s revolutionary finding was that the timing of these conscious decisions was consistently preceded by several hundred milliseconds of background preparatory brain activity (known technically as “the readiness potential”).
The implication was that the decision to move was made nonconsciously, and that the subjective feeling of having made this decision is tagged on afterward. In other words, the results implied that free will as we know it is an illusion — after all, how can our conscious decisions be truly free if they come after the brain has already started preparing for them?
For years, various research teams have tried to pick holes in Libet’s original research. It’s been pointed out, for example, that it’s pretty tricky for people to accurately report the time that they made their conscious decision. But, until recently, the broad implications of the finding have weathered these criticisms, at least in the eyes of many hard-nosed neuroscientists, and over the last decade or so his basic result has been replicated and built upon with ever more advanced methods such as fMRIand the direct recording of neuronal activity using implanted electrodes.
Luckily, for those who find this state of affairs philosophically (or existentially) perplexing, things are starting to look up. Thanks to some new breakthrough studies, including one published last month inProceedings of the National Academy of Sciences by researchers in Germany, there’s now some evidence pointing in the other direction: The neuroscientists are backtracking on past bold claims and painting a rather more appealing account of human autonomy. We may have more control over certain processes than those initial experiments indicated.
The German neuroscientists took a different approach from past work, using a form of brain-computer integration to see whether participants could cancel a movement after the onset of the nonconscious preparatory brain activity identified by Libet. If they could, it would be a sign that humans can consciously intervene and “veto” processes that neuroscience has previously considered automatic and beyond willful control.
The participants’ task started off simply enough: They had to press a foot pedal as quickly as possible whenever they saw a green light and cancel this movement whenever they saw a red light. Things got trickier when the researchers put the red light under the control of a computer that was monitoring the participants’ own brain waves. Whenever the computer detected signs of nonconscious preparatory brain activity, it switched on the red light. If this preparatory activity is truly a signal of actions that are beyond conscious control, the participants should have been incapable of responding to these sudden red lights. In fact, in many cases the participants were able to cancel the nonconscious preparatory brain activity and stop their foot movement before it even began.
Now, there was a point of no return — red lights that appeared too close (less than about one-quarter of a second) to the beginning of a foot movement could not be completely inhibited — there simply wasn’t time for the new cancellation signal to overtake the earlier command to move. But still, the principle stands — these results suggest at least some of the activity identified by Libet can, in fact, be vetoed by conscious will.
“A person's decisions are not at the mercy of unconscious and early brain waves,” the lead researcher, Dr. John-Dylan Haynes of Charité - Universitätsmedizin in Berlin, said in the study’s press release. “They are able to actively intervene in the decision-making process and interrupt a movement. Previously people have used the preparatory brain signals to argue against free will. Our study now shows that the freedom is much less limited than previously thought.”
This new finding comes on the back of research by French neuroscientistspublished in 2012 in PNAS that also challenged the way Libet’s seminal work is usually interpreted. These researchers believe that the supposedly nonconscious preparatory brain activity identified by Libet is really just part of a fairly random ebb and flow of background neural activity, and that movements occur when this activity crosses a certain threshold. By this account, people’s willful movements should be quicker when they’re made at a time that just happens to coincide with when the background ebb and flow of activity is on a high point.
And that’s exactly what the French team found. They recorded participants’ brain waves as they repeatedly pressed a button with their finger, sometimes spontaneously at times of their own choosing, and other times in response to a randomly occurring click sound. The researchers found that their participants were much quicker to respond to the click sounds when the sounds happened to occur just as this random background brain activity was reaching a peak.
Based on this result from 2012 and a similar finding in a study with rats published in 2014, the lead researcher of the 2012 study, Aaron Schurger at INSERM in Paris, and two colleagues have written in their field’s prestige journal Trends in Cognitive Sciences that it’s time for a new perspective on Libet’s results — they say that their results call “for a reevaluation and reinterpretation of a large body of work” and that for 50 years their field may have been “measuring, mapping and analyzing what may turn out to be a reliable accident: the cortical readiness potential.”
And like their counterparts in Germany, these neuroscientists say the new picture is much more in keeping with our intuitive sense of our free will. When we form a vague intention to move, they explain, this mind-set feeds into the background ebb and flow of neural activity, but the specific decision to act only occurs when the neural activity passes a key threshold — and our all-important subjective feeling of deciding happens at this point or a brief instant afterward. “All this leaves our common sense picture largely intact,” they write.
I’ll leave you to decide whether to believe them or not.
Dr. Christian Jarrett via NY Mag Science of Us
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