This is one of the most famous experiments in the field of neuroscience, which still causes fierce scientific debate. In 1983, American psychologist Benjamin Libet showed that our sense of free will may actually be an illusion. Libet’s experiment had three important components: a choice situation, a measurement of brain activity, and a clock. The choice situation consisted in the fact that the subject was offered a choice to move his left or right hand. In the original version of the experiment, participants moved their wrist; in some subsequent versions, they had to raise a finger on their left or right hand. Participants in Libet’s experiment were warned “that the desire to move one’s arm should arise spontaneously,” and that they should neither plan the movement in advance nor concentrate on exactly when to make it. The exact moment of wrist movement was recorded by muscle contraction using sensors attached to the arms. Changes in brain activity were measured using electrodes attached to the head above the motor area of the cerebral cortex (approximately above the crown). When a person decides to make a move, electrical signals arise in the brain – the so-called readiness potential. Moreover, the signals differ for the right and left halves, and this difference is obvious when analyzing brain activity. The clock was designed in such a way that the subjects could determine the time with an accuracy of fractions of a second. The light dot on the dial ran a full circle every 2.56 seconds. By determining the position of the point on the dial, it was possible to determine the exact time. If we assume that a person is able to determine the position of a point with an accuracy of an angular magnitude of 5 degrees, then such a watch can be used to measure time with an accuracy of 36 milliseconds, that is, 36 thousandths of a second. Libet introduced another factor into his experiment. Participants were asked to use a watch to report the exact time when they decided to move their wrist. An analysis of the subjects’ brain activity showed that the decision to move their wrist was usually made by them before they realized that they had made this movement. Physiologists had known for decades that the readiness potential in the brain occurs a fraction of a second before a person makes a move. Libet’s experiment revealed the same thing – the readiness potential appeared a fraction of a second before the wrist movement was registered.   However, the most surprising thing came out when analyzing the participants’ messages about exactly when, in their opinion, they decided to make a move. This happened in the interval between the emergence of the readiness potential and the actual movement. In other words, the subjective feeling of making a decision to move your wrist occurred later than the potential for readiness. In a sense, the decision had already been made before the subjects realized it. Did the participants in the experiment actually make a conscious decision, or was their sense of freedom of choice just an illusion? The debate about this continues to this day. Libet’s experiment is not the only scientific study that provides food for debate about free will in the context of neuroscience, but its simplicity and clarity haunt both those who believe that belonging to biological beings imposes certain restrictions on our expression of will, and those who think that free will is not so dependent on biology.. Part of the surprise that the results of Libet’s experiment cause is due to two very common beliefs about the nature of the mind. The first of these is the intuitive feeling that the human mind exists separately from the material body. It is because of this dualism that people tend to imagine the mind as something pure and abstract, not constrained by a biological shell. This illusion is easy to destroy if we remember that people who are hungry are often out of sorts, but still this belief is very firmly rooted in our minds. Otherwise, it would not surprise us that our thoughts and experiences correspond to electrical impulses in the brain. If we really sincerely believed that the mind resides in the brain, we would take for granted the fact that every change in the state of mind is accompanied by brain activity. The second common belief is the belief that we know enough about our own mind. We believe that our subjective sense of decision-making is a reliable source of information about how these decisions are made. The mind is like a machine: as long as it works smoothly, we are happily unaware of the mechanisms of its functioning. It’s only when faced with errors or contradictions that we think to look under the hood. Why didn’t I pay attention to this detail? How could I forget that person’s name? Or: why does the feeling of decision-making arise after the emergence of a potential for readiness? There is no reason to believe that our perception of our own mind is completely objective. On the contrary, psychology provides us with a large number of examples of how often we make mistakes. The feeling of decision-making that arises in Libet’s experiment may be completely illusory – perhaps, in fact, the decision is somehow made by the brain without the conscious participation of its owner. Or there is simply a delay between the decision-making process and the appearance of the corresponding sensation. The mere fact that our perception of the moment of making a decision does not correspond to the true moment does not necessarily mean that we were not directly involved in this process in one way or another. More and more scientific articles are published about Libet’s experiment every year. He gave birth to an entire academic branch that studies free will from a neurobiological point of view. There is no shortage of criticism of the applicability of the experiment to everyday freedom of choice. Even Libet’s supporters have to admit that the situation used in his experiment may be too artificial to reliably simulate the real choice situations that we all face every day. But this simple experiment continues to fuel scientific debate and encourage scientists to come up with new hypotheses about the connection between freedom of choice and brain activity. And all because Libet has clearly shown how much more complex the human mind is than it seems to us. Source: BBC