Electrical signals in the brain. Credit: Henrik5000/iStock
The question of whether we are free to choose or whether our actions are pre-determined goes to the core of how we think of ourselves as humans. Can studying brain activity tell us more about free will?
The Plan to Move: “Bereitschaftspotential”
The existence and nature of free will have been debated by philosophers, theologians and economists for millennia. With the advent of modern neuroscience, it became possible to study the brain in detail. (Nobel Laureate Erwin Neher talked about the communication between synapses during the Lindau Nobel Laureate Meeting 2014, you can learn about it in our mediatheque.) It was then only a matter of time before ambitious and capable researchers attempted to understand the neuroscience behind volition. One of the first forays into this field was made in the mid-1960s by researchers in Freiburg in southern Germany. Hans Helmut Kornhuber and Lüder Deecke wished to move beyond brain research that focused on how the organ responds to the world around it to an understanding of how the brain plans and executes movements. Kornhuber and Deecke used external measurements of the brain’s electrical activity, to analyse what happens in the brain just before movement. They found electrical processes in the brain that preceded and thus seem to plan for the voluntary movement. They termed these processes the Bereitschaftspotential (readiness potential).
This was a profoundly important experiment – Kornhuber and Deecke could show for the first time that will is reflected in electrical processes in the brain. Nobel Laureate John Eccles, who was awarded his prize for work on the synapse, compared their experiments to those performed by Galileo Galilei to unravel the laws of motion some 400 years earlier. What came next was a lot more surprising – and controversial.
Free Will: a Controversial Debate
Kornhuber and Deecke’s line of inquiry was based on the belief that humans do have free will, but the highly influential experiments of the American neuroscientist Benjamin Libet – performed some 20 years after those of Kornhuber and Deecke – called this assumption into question. Libet’s primary interest was in the phenomenon of consciousness. In his experiments, he measured the Bereitschaftspotential from the brains of subjects who were asked to make a simple motor movement. Subjects were also asked to indicate the point in time at which they became conscious of their desire to move. Surprisingly, Libet found that the Bereitschaftspotential preceded consciousness of the impending action, i.e., the brain prepares for movement even before you are aware of it. Needless to say, Libet’s conclusions were and remain controversial, and were used by some to conclude that free will, the conscious planning and then execution of actions, is all an illusion.
The most important scientific challenge to Libet’s work calls into question the interpretation of what the Bereitschaftspotential actually is. Much of this work has been carried out in the last ten years by Aaron Schurger, a brain researcher based in France, together with colleagues. In essence, he argues that the Bereitschaftspotential is merely a snapshot of background brain ‘noise’, which is continuously waxing and waning below the threshold which is required for the initiation of movement. Thus, simply because a Bereitschaftspotential can be measured before the conscious decision to move does not mean that this process is responsible for that movement, and decisions are not made when a Bereitschaftspotential starts, but rather when it crosses a threshold which triggers movement.
The Current State of the Debate Around the Bereitschaftspotential
Is the neural noise just noise, though? A study published in February 2020 now suggests that there is more to it than that. Information from inside our body, such as breathing and input from our visceral organs, is known to be one cause of the constant fluctuations in brain activity. Breathing is particularly interesting in this regard: it is under the control of the same brain region that is responsible for the Bereitschaftspotential, and it is synchronised with movement in mammals. Researchers led by Hyeong-Dong Park and Olaf Blanke in Geneva, Switzerland explicitly tested this hypothesis. They performed the same classic experiments as those of Kornnhuber and Deecke and Libet and also monitored the breathing of the subjects as they made movements. They found that voluntary movement as well as the Bereitschaftspotential are indeed linked to breathing: subjects were much more likely to initiate a voluntary action when breathing out than while breathing in, and the Bereitschaftspotential was generally lower when subjects were breathing out.
These are intriguing observations. What do they mean for the execution of voluntary actions and for the concept of free will? On the one hand, they lend support to the idea that the Bereitschaftspotential reflects natural fluctuations in brain activity; however, these new findings also demonstrate that these natural fluctuations are not random but are rather under the control of respiration. They also suggest that the Bereitschaftspotential is not our brain “knowing” what we want to do before we do, but rather reflects the brain’s need to balance the involuntary (breathing) with the voluntary (movement).