On free will-11: Recent fMRI studies of the brain

(For previous posts in this series, see here.)

In a recent paper (Unconscious determinants of free decisions in the human brain, Chun Siong Soon, Marcel Brass, Hans-Jochen Heinze, & John-Dylan Haynes, Nature Neuroscience, vol. 11, no. 5, May 2008, 543-545), researchers used the more sophisticated modern technique of fMRI (functional magnetic resonance imaging) to measure brain activity. The paper is not available online without a subscription but you can read a news report on the results of their paper here.

This experiment was designed to meet two key concerns about the Libet studies: that the time interval between act and the precursor unconscious brain activity prior to act was too small to definitively rule out measurement errors, and that Libet’s team had not shown that the early brain activity was a predictor of a specific decision.

The fMRI studies find that our decisions as to what actions we will take originate in our unconscious neural activity and only later informs our conscious mind of it, thus providing strong evidence against the existence of free will. The paper describes what the researchers asked their test subjects to do while they were hooked up to fMRI measuring devices.

The subjects were asked to relax while fixating on the center of the screen where a stream of letters was presented. At some point, when they felt the urge to do so, they were to freely decide between one of two buttons, operated by the left and right index fingers, and press it immediately. In parallel, they should remember the letter presented when their motor decision was consciously made. After subjects pressed their freely chosen response button, a ‘response mapping’ screen with four choices appeared. The subjects indicated when they had made their motor decision by selecting the corresponding letter with a second button press. After a delay, the letter stream started again and a new trial began.

Each letter was shown on the screen for 500 ms before switching to a new one and this was the time marker used by the researchers to determine when the decision to push a button was made. Note that in this experiment there are two decisions involved: when to push a button and which button to push. The fMRI data enabled the researchers to use sophisticated decoding computer programs to detect predictive signal patterns in brain activity, even in the absence of an overall increased signal strength, the latter being what the earlier experiments had depended upon. This enabled the detection of far more subtle effects.

In the trials it turned out that patients pushed both left and right buttons equally often and they were conscious of the decision to press within a time interval of one second before actually pressing a button.

But it is the other results of the experiment that are dramatic. Soon et. al. found that there was precursor activity in regions of the brain other than the SMA regions probed by Libet, and that this activity occurred much earlier than the SMA activity. Furthermore, this activity also predicted which button was going to be pushed.

[T]wo specific regions in the frontal and parietal cortex of the human brain had considerable information that predicted the outcome of a motor decision the subject had not yet consciously made. This suggests that when the subject’s decision reached awareness it had been influenced by unconscious brain activity for up to 10 s. (my italics)

Notably, the lead times are too long to be explained by any timing inaccuracies in reporting the onset of awareness, which was a major criticism of previous studies. The temporal ordering of information suggests a tentative causal model of information flow, where the earliest unconscious precursors of the motor decision originated in frontopolar cortex, from where they influenced the buildup of decision-related information in the precuneus and later in SMA, where it remained unconscious for up to a few seconds.

This figure shows the time sequence of events that the study revealed.


The earliest precursors of an action lie in regions of the brain other than the SMA, which is the region that caused the electrophysiological effects that Libet was measuring, which explains why Libet (and Grey Walter before him) got just a half-second lead time while now it is a whopping 10 seconds. The new fMRI studies also enabled the researchers to determine that the leading brain activity selectively predicted the outcome of the subject’s choice of which button to push, and was not simply indicative of some nonspecific preparatory processes, which was the criticism made by Trevenna and Miller of the Libet team’s experiments.

They also found that the decision to push a button could be predicted up to five seconds before the act, and this information was present in the SMA and pre-SMA regions of the brain.

In this video clip, Marcus Du Sautoy records his experience of participating in this same experiment. (Incidentally, Du Sautoy, Professor of Mathematics at the University of Oxford, is the successor to Richard Dawkins as holder of the Simonyi Professorship for the Public Understanding of Science.)

Note that the predictions of which button to push were not perfect, with only around 60% accuracy. The absence of 100% accuracy is probably due to the lack of precision of the detecting apparatus and inadequacies of the pattern-recognition software, both of which are bound to get more sophisticated with time, thus increasing the accuracy of predictions. But the fact that the result is better than chance means that, as lead author Haynes says, “there’s not very much space for operation of free will” because “[t]he outcome of a decision is shaped very strongly by brain activity much earlier than the point in time when you feel to be making a decision.” Other researchers concur.

Dick Passingham, a cognitive neuroscientist at the University of Oxford in the U.K., says the paper clears up one of the major concerns about the original Libet experiment. “This activity that occurs earlier is … not just general preparation, it really is a proper decision,” he says.

Neurologist Mark Hallett of the U.S. National Institute of Neurological Disorders and Stroke in Bethesda, Maryland, says the study confirms his understanding of free will as a perception rather than a driving force.

This seems to pretty much kill the idea of free will as traditionally understood. As biologist Anthony Cashmore says, “The reality is, not only do we have no more free will than a fly or a bacterium, in actuality we have no more free will than a bowl of sugar. The laws of nature are uniform throughout, and these laws do not accommodate the concept of free will.”

The Ghost in the Machine seems to be well and truly exorcised.

Next: What about quick decisions?


  1. henry says

    I’ve been thinking about the Anthony Cashmore quote today where he says, “The reality is, not only do we have no more free will than a fly or a bacterium, in actuality we have no more free will than a bowl of sugar. The laws of nature are uniform throughout….”

    If we accept this as true then is killing a fly the same as killing a human?

    If we are just biology and there is no separate self then what is to distinguish us from any other species with regards to rights or privileges?

  2. says

    There are no “rights or priviledges”.

    Who would bestow them?

    We are a species like any other species, except we have self-conscious brains that can solve more complex problems than other species.

    Other species may or may not have self consciousness. Almost certainly other mammals do. But almost certainly a fly does not.

    The dilemma is where the division lies, and this requires more scientific work.

    A good book on the moral implications of free will is Saul Smilansky’s “Free Will and Illusion”.

  3. says

    Yes….where “fittest” is the best adapted species to the environment.

    That doesn’t mean as modern humans we need to behave like nature behaves. But that is how nature behaves.

    Humans have evolved a sense of morality, so we attempt to discern moral differences between killing a fly and another human, and act accordingly.

  4. says

    It seems to me that there is a bit of a “chicken and egg” conundrum here. The researcher in the video explains to Marcus that the unconscious mind -- the part of the brain that appears to be formulating the decision several seconds before the conscious mind -- “is in harmony with your beliefs and desires” and tends to act in accordance therewith. The question then becomes, where are those beliefs and desires? How did they come to impress themselves upon the unconscious mind/brain?

    If we still have the freedom to choose particular beliefs or, to build on Mano’s example, the freedom to decide that we should inculcate good habits in our activities, then we have the freedom to influence the evolution of the neuronal pathways that will actualize those beliefs later on.

    Thus, I take this research to mean that decisions and actions are the result of a two-way conversation, conducted over an extended period of time, between conscious and unconscious levels of the mind/brain. Free will has not been eliminated; it has moved from the level of micro-managing quotidian minutiae to the macro level of beliefs and desires. We set the course; the brain handles all the travel arrangements.

  5. says

    R. Frost --

    Absolutely not. No conundrum, no free will.

    Those beliefs and desires are in your brain. Part of their origination is a result of evolution and get put into your brain during brain development when you were a fetus.

    Some of those beliefs and desires you learn, either unconsciously or consciously.

    Some of those beliefs and desires you are consciously aware of sometimes, some you’re not.

    The brain sets the course (taking advantage of sensory input) AND it handles all the travel arrangements (using the autonomic nervous system to control functions you’re usually not conscious of, and the somatic nervous system for conscious control).

    Things have to be in harmony…or we feel sick or distressed until things are in harmony. Illusions and magic tricks play on the brain’s need for harmony and they fool that need. When our brain is disharmonious, we feel sick…from sea sickness to depression to denial.

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