National Geographic

Unconscious brain activity shapes our decisions

Blogging on Peer-Reviewed ResearchOur brains are shaping our decisions long before we become consciously aware of them. That’s the conclusion of a remarkable new study which shows that patterns of activity in certain parts of our brain can predict the outcome of a decision seconds before we’re even aware that we’re making one.

Redpill.jpgIt seems natural to think that we carry out actions after consciously deciding to do so. I decide to start typing and as a result, my hands move around a keyboard. But according to modern neuroscience, that feeling of free will may be an illusion. For over twenty years, experiments have suggested that, unbeknownst to us, a large amount of mental processing goes on in unconsciously before we become aware that we intend to act.

The first such study was done by Benjamin Libet in 1983. Libet asked volunteers to press a button at a time of their choice, and to remember the position of the second hand of a wristwatch when they first felt the urge to move. While this happened, Libet measured the activity of their supplementary motor area (SMA), a part of the brain involved in planning movements. Astonishingly, he found that the SMA  became active about half a second before the volunteer felt a conscious desire to press the button.

The seminal experiment suggested that the brain makes decisions on a subconscious level and that people only believe that they consciously drove their actions in hindsight. The experiment seemed to put a dent in beliefs about free will and understandably, it has proved to be controversial. Some have criticised the techniques that Libet used, claiming that inaccurate measurements could explain that the small gap between brain activity and conscious awareness.

For those who were convinced by the experiment’s results, a slew of important questions remained. Is the SMA the source of the decision, or is it responding to other parts of the brain even higher up the chain of command? And is this unconscious activity a sign that the relevant areas of the brain are revving into readiness, or does it actually predict the action that is eventually taken? Now, Chong Siong Soon and colleagues from the Max Planck Institute have addressed these queries with an elegant update of Libet’s work.

Pick a button, any button

Thinker.jpgSoon asked 36 volunteers to watch a letter in the centre of a computer screen, that changed every half-second. As the letters streamed by, the volunteers had to press one of two buttons, whenever they felt like it. When that happened, they were given a choice of four letters and had to choose the one that was up when they made their button-pressing decision. 

As they did this, Soon measured their brain activity using a scanning technique called functional magnetic resonance imaging (fMRI). He then used a statistical technique called pattern recognition to see if he could match the patterns of activity in different parts of the brain at different times with the choice to press the right or left button.

On average, the volunteers took about 22 seconds to press the button and felt that they consciously decided to do so about a second or less before they made the movement. But the fMRI data told a much different story. Two parts of the brain – the frontopolar cortex and the precuneus -showed activity that predicted the choices that the volunteers made and in the frontopolar cortex, this activity happened a whopping 7 seconds before the subjects were consciously aware of their decisions. 

These astonishing results suggest that by the time we become consciously aware of a decision to move, our choices have already been influenced for several seconds by the actions of the frontopolar cortex. The study goes well beyond Libet’s original work. It shows that this preliminary activity is far from a general and non-specific curiosity, but can actually predict a decision. Nor can it be explained away by inaccuracies in measurement – the timescales involved were far too long for that.

These associations have never been seen until now because neither the frontopolar cortex not the precuneus were more active in total in the time leading up to the button press. Instead, it was the pattern of firing neurons within these areas that predicted the final decision, and it took the use of pattern recognition techniques for this effect come to light.

Chain of events

The involvement of the frontopolar cortex isn’t surprising. It fulfils the role of an executive manager and is involved in retrieving memories and controlling other high-level parts in the brain. Soon thinks that it is the source of the decision itself, with the precuneus simply storing the decision until it reaches a conscious level. When he changed his experiment so that volunteers were shown a cue to tell them when to make their choice, the frontopolar cortex still showed predictive activity before the signal, but the precuneus only did so in the time between signal and action.

Soon found, as Libet did, that the SMA was also active before the volunteers became conscious about their intentions. But he also showed that its pattern of activity can predict when the final decision is made. Again, this information is available at an unconscious level about 5 seconds before the volunteers actually move. The frontopolar and parietal cortex aren’t involved in timing until the few milliseconds before the movement, so it seems that the two parts of the brain have different and complementary duties. One shapes the outcome of a choice and the other affects its timing.

Soon tentatively suggests that the sparks of a decision begin in the frontopolar cortex. From there, the decision is ‘prepared’ by the buildup of activity in the precuneus and later, the SMA. It is held there for a short while before we become consciously aware of it and act. This unconscious part of the decision-making process may be for our own good. At least one experiment showed that people with damage to the relevant parts of the brain don’t show any signs of unconscious preparation and make poorer decisions in a gambling experiment.

Studies like these have important philosophical implications. If our brains unconsciously make our decisions for us, is there any room for free will? Libet himself thinks so, but only in a restricted way. He asserts that for all the brain’s unconscious preparation, people can still consciously decide to stop performing an action in the final milliseconds before thought becomes deed. In this view, it’s more a case of “free won’t” than free will. 

Reference: Soon, C.S., Brass, M., Heinze, H., Haynes, J. (2008). Unconscious determinants of free decisions in the human brain. Nature Neuroscience DOI: 10.1038/nn.2112

Images: Thinker photo by Satyakamk

Add Yours.

  1. royniles
    April 13, 2008

    There’s no reason to assume we don’t have free will just because we aren’t conscious of the decision making process. There’s still a decision process that our brains are just as free, or not free, to make one way or the other (assuming they were at all free to make decisions to begin with). The ability to consciously choose what information to look at, that then becomes part of the basis for making unconscious inferences, is where the nexus of the free will dilemma sits. Are those conscious choices predetermined, or at least an inevitable consequence of physical laws governing cause and effect? That’s the real question, and there has so far been no reliable answer except that on balance we can expect to be better off by acting as if we have free will, regardless of our philosophies.

  2. GAC
    April 13, 2008

    I’d actually be interested in experiments as to whether people can stop a decision that’s be unconsciously prepared. I’ve long wondered if my decisions were made unconsciously and only rationalized afterward, but I can also think of times when I had decided to do something and then stopped myself — but it’s equivocal as sometimes I only stopped myself a few seconds after I started. Perhaps researchers could assign a task, and then ask people to decide when to stop performing that task.

  3. Anon
    April 13, 2008

    But royniles, there’s no reason to assume we *do* have free will, either. Certainly not in the classic sense of a conscious, independent, decision-making unmoved mover.
    And we must not confuse “determined” with “predetermined”–quite a lot of what shapes our behavior is selection by consequences of actions, not a billiard-ball determinism. Evolution by natural selection is determined, but it is certainly not predetermined. The consequences of our actions increase or decrease the probability of those actions in the future in a deterministic and lawful manner.
    Acting *as if* we have free will is useful because it does highlight the consequences of our actions rather than the antecedents. I would argue, though, that planning a society is best served by assuming we *do not* have free will, and that our environments shape our behavior. Build schools now, and you won’t have to spend as much on prisons later.

  4. mogmich
    April 13, 2008

    It’s hard to see why we should have a consciousness at all, if the conscious decision is delayed in time this way.
    There’s another possibility, which could explain why we have a consciousness. Unfortunately this seems to be a violation of physics: That consciousness have a limited capability to influence the past!
    1) An unconscious process prepares the decision in one part of the brain.
    2) The decision becomes conscious.
    3) Consciousness somehow determine or change the pattern of activity in another part of the brain – a few seconds back in time!
    4) This activity determine the act.
    Sounds crazy, but wouldn’t it have a clear survival value in nature?

  5. Anon
    April 13, 2008

    That’s one heck of a lot for a “somehow” to do in step three, mogmich. There are other theories of consciousness that don’t require backward causation. The only trick is, none of the logically coherent ones allow for a causal conscious free will in the classic sense.

  6. Sean Nicolle
    April 13, 2008

    This has nothing to do with free will. You “choose” to respond to your urges. And many times, you choose not to.
    In my humble opinion, the debate between free will and determinism is just semantic trickery. We confuse the rules that govern language with an all-pervasive reality. Pffft. Or maybe the term “free will” is just vague, ill-conceived, and entirely misapplied.
    We neither have nor do not have free will.

  7. El Christador
    April 13, 2008

    There are two free will versus determinism debates. One determinism definition is “hard” determinism, which is AFAICT, that the equations of physics describe a unique solution from a given initial condition. This is the one I find interesting.
    Then there’s “soft” determinism, which is something for which I don’t know exactly what the term means, but it seems to be kind of just the question of whether we’re at the mercy of circumstance and the situations that we find ourselves in. Not too interesting to me.
    Discussions of free will tend to have the trouble of coming up with a satisfactory definition. The definition I like is in terms of the uniqueness of solutions to an initial value problem.
    Another point that always comes up and is worth emphasizing, is that the existence of a decision-making process is not the same as “free will” (under some definitions, anyway). There is no reason why a deterministically operating machine can’t make decisions — computers do it all the time. So it’s certainly true that our brains make decisions and a choice-making process exists, but if the brain is operating deterministically (i.e. if given sufficient information about the initial conditions some time in the past, we could predict with certainty what the outcome will be up to some specified time in the future) then it would not mean that we have “free” will (again, depending on the definition you like). That is, choice may exist, but that doesn’t mean it’s necessarily a “free” choice.
    It seems that often what people mean when they say “free” will could best be described as “endogenous” will i.e. is the decision coming from “within” us? That relates more to the “soft determinism” definition of free will, it seems to me.
    Note that, at least in the “hard determinism” sense, free will has much the same status as God: there are no observations that require it in order to be explained, it doesn’t fit well into the current picture of the universe we have, if it does exist then it’s lurking in one of the few remaining corners we don’t fully understand yet (such as the quantum measurement process, in the case of “free will”), and the main reason people believe in it seems to be for their own personal emotional reasons.

  8. El Christador
    April 13, 2008

    Anon: I’m not clear on the difference between “determined” and “predetermined” according to your definitions.

  9. Hank Roberts
    April 13, 2008

    Thanks for the link to
    http://www.sciencemag.org/cgi/content/abstract/275/5304/1293
    and its wonderful collection of citations; following that work forward through the past decade, we’ve learned a lot.
    Including a lot about why it’s easier to cheat old people, when those unconscious evaluation processes have started to get unreliable with increasing age in some people.
    Let’s just hope nobody tells the mortgage brokers and check cashing shops about this.
    Oh, wait …

  10. raiko
    April 14, 2008

    I agree with royniles here. I don’t see why the unconsciousness of a decision would exclude having a free will about that very – unless anyone every thought that free will is detached from brain function. If you accept that even free will is a complicated form of brain function, then whether that decision is conscious or unconscious is not so important.

  11. Nomen Nescio
    April 14, 2008

    seven seconds is longer than we often have to make decisions — snap judgments about how to navigate a vehicle in traffic often have to be made and executed based on information more recent than that, just for the obvious example. could this experiment be highlighting a special case of cognition?
    also, i’m wary of speaking about “the unconscious” as if it were some alien homunculus with a personality all its own pulling the strings of my brain when i’m not watching. what’s being seen on these fMRI’s could just as easily be the infrastructures that generate consciousness at work, in my opinion.

  12. BAllanJ
    April 14, 2008

    The post and comments are all referring to normal subjects, but perhaps this finding’s chief benefit may be in studying abnormal subjects. Maybe the amount of time between subconscious and conscious decision would be a useful parameter for diagnosing and studying people who aren’t functioning as well as others. (I’m grabbing this a bit from an odd little scifi paper by Isaac Asimov on Thiotimolene from at least 25 years ago)

  13. gerald spezio
    April 14, 2008

    Your lucid discussion of Soon’s powerful empirical update of Libet’s earlier revelations is as good as it gets.
    Your love of science and your ability to share that love shines through.
    Are you sure that you aren’t Italian?

  14. TSK
    April 14, 2008

    But he also showed that its pattern of activity can predict when the final decision is made. Again, this information is available at an unconscious level about 5 seconds before the volunteers actually move.
    No, it isn’t. Unfortunately you forgot to mention the actual prediction rates: 60% before the conscious decision and 75% after conscious decision when SMA peaks activity.
    To sell 60% in contrast to a random 50% chance as “prediction” is spin, not science.
    And Libet’s did not just “think”. It is frustating that every time people come up with Libets experiments to “prove”
    the non-existence of free will that they convieniently forget the last experiment: Libet asked the participants to reverse their decision on a signal. So he found out that the point of no return is actually 0,1-0,2 seconds before the final action, the observed increase in SMA is therefore the preparation of movement, not a valid predictor of the outcome.

  15. Ed Yong
    April 15, 2008

    Great comments everyone – I’ve certainly learnt a lot from them. I’m pretty sure I’m not Italian unless my parents aren’t telling me something. The 60% prediction rate is low, but from the paper, it was also statistically significant. For readers wanting more on this, have a look at Steven Novella’s excellent write-up at NeuroLogica.

  16. Alice Yong
    April 15, 2008

    Nope, you’re not Italian unless my parents aren’t telling me something! – Mummy.

  17. Toni Honkala
    April 16, 2008

    First of all, it seems all scientific research has problems in their core, if seen from the point of view of autonomist epistemology. That is, the possibility to know anything at all (through senses and properly working cognition) relies on the presumption of the validity of sense perception and cognition of the perceiver. These has to be justified on the basis of themselves. This is circular reasoning.
    Secondly, and very interestingly, in some India books, written in sanksrit, the problem of free will is explained in a way, that bears similarities with these neuroscientific explanations presented by researchers.
    In short, according to these scriptures the feeling (illusion) of free will happens due to the identification of consciousness (or maybe more precisely consciouss awareness) to the body-mind. Scriptures bring forth, that body-mind in under total conduction of the gunas, which are basic principles constructing the whole of the manifested universe (prakrti).
    Of course the language of used in this books and in their translations is somewhat different comparing to neuroscientifical language, but the ideas seem really similar. Except, that these neuroscientific explanation can, very understandingly, deal only with the so called natural world due to the theoretical and empirical resctrictions of natural sciences.
    In these sanskrit books supernatural realms are presupposed. And supernatural means, according to present understanding observable in the body-mind of the writer of this text, something that is beyond the capabilities of human sense perceptions and cognitive capacities.
    Here’s a link to one verse:
    http://www.bhagavad-gita.org/Gita/verse-03-27.html

  18. Tom Michael
    May 2, 2008

    The study has appeared on a number of blogs in a number of different contexts but always making the same point – that imaging can detect activity which suggests the decision to press a left or right button is made a number of milliseconds BEFORE we are consciously aware of having made the decision. The accuracy of the prediction based on imaging has been reported at approximately 60% if I recall correctly.
    Whilst this accuracy is greater than chance, meaning the prediction has some validity, I think that the conclusion that humans only have an illusion of free will is a very poor one. The decision to press a left or right button is essentially a “random” decision, as random as choosing A or B can ever be from within your own mind, rather than flipping a coin. My point is that, in a “random” decision such as this, is it really surprising that micropatterns in neural activity, which could easily be described as neural “noise” give the person a subconcious inclination to chose one button over another? As the person may feel they are choosing the button “at random” using their own “free will” this is not surprising at all.
    Now, if we consider a “reasoned” as opposed to “random” use of free will, the pattern might be very different. Consider quitting smoking cigarettes, which is a hard act of free will, requiring “willpower”. In this case, although it is not yet possible to detect this, we could hypothesize that there would be micropatterns in neural activity relating to dopamine activation of synapses following nicotine inhalation, that give the person a subconcious craving to continue smoking. If an MRI scanner could detect this activity, we might be able to predict if a person would find it easier or harder to quit smoking, with say, 60% accuracy.
    Whilst it is arguable that a person might not be able to quit cigarettes if the addiction and craving exceeds their “willpower” it is ridiculous to argue that the person in the study above would not have been able to change their mind and press a different button, should they so wish. This ability, to inhibit our actions and responses, is tested by neuropsychological tests such as the Stroop Test. I would argue that the ability to inhibit our actions and/or change our minds, examples of Executive Function, are an example of a limited capacity for “Free Will” or “Willpower”. The fact that we might chose button A randomly over button B and that this random decision is influenced by neural noise of which we are not conscious does nothing to disprove the concept of Free Will.
    PS: I work with patients with Frontal Lobe brain injuries (Dysexecutive Syndrome) who show problems in decision making, planning and inhibition of behaviour. They are, in short, driven much more by environmental stimuli and much less by internal willpower. One could even go so far as to suggest that they have a willpower deficit or damage.
    The philosophical and spiritual points raised above are interesting, but until you meet someone who is unable to inhibit their behaviour (even to the point of aggression or inappropriate sexual behaviour) due to brain damage, you really can’t “say” how the brain “works” in terms of Free Will. Neither can I by the way, I just think I’ve observed this kind of thing a little more than many…

  19. Ronald K. Olson
    September 21, 2008

    I’m a little late into the fray, but…
    If consciousness is an after the fact phenomenon as Libet and Soon seem to have established, then our consciousness is never involved in the “decision.” In this instance, the use of the word, “decision,” is thoroughly misleading. Our natural, intuition-based, proclivity is to comprehend the word, “decision,” in terms of a conscious manipulation of data. Soon and Libet pretty well put the cabbosh on that. I believe it is more accurate to use the terms “effect,” or “response,” as in, cause and effect, or stimuli and response. The quantum level activity within the brain is copious with an exponent somewhere in the millions! This almost instantaneous storage and retrieval, cross referencing and catagorizing, weighting and analyzing, manipulating and rationalizing, using the massive amounts of incoming data experienced in the conscious hours of our day is beyond man’s ability to imagine, much less devise and construct mathematic models which explain it! This is no reason to deny that brain activity is a result of the mathematic laws of physics given meaning through the cause and effect continuum. As is so often the case, man has a rather elevated perception of himself. Sure, the physics of the human brain is preposterously complex, but so is a galaxy, a super nova, or even a cloud formation. Yet, self-aggrandizingly we assume man makes decisions, but galaxies, super novas and clouds do not.
    I would also like to energetically suggest that living in a determined universe as if it were a free-will universe is akin to breathing water as if it were air! If Soon and Libet have put free-will on life support, then the history of mankind has nailed the lid on free-will’s coffin! From the insertion of mankind into the evolutionary continuum, it has tried its damnedest to make this free-will thing work. For all of mankind’s noble efforts, civilization after civilization after civilization rises and falls, rises and falls, rises and falls. So powerful is this free-will intuition, each of these attempts at civilization have gone to their graves embracing the traitorous assassin within their hearts and minds; the free-will mindset. Mankind is now to the point of causing its own extinction along with the extinction of much of the life having the misfortune of living on the same planet, simply because mankind thinks it is special.
    Certainly, there are psychological, social, and spiritual ramifications. Just as certain is mankind’s aversion to change. But equally certain is the reality that whatever it is we have done in the past to get us where we are today, if we keep doing it, fairly soon there will be an unbelievably large pile of rotting flesh at the bottom of the cliff, and it won’t just be buffalo meat!
    If this tweaks your curiosity, log on to: http://www.beneficentparentalism.com. Free-will isn’t all it’s cracked up to be, and determinism is a whole lot warmer than you might think.
    rko

  20. tmaxPA
    November 3, 2010

    Free Will == Phlogiston

    Unconscious brain activity IS our decisions. I thought it was already pretty well confirmed by psychology that we make our decisions ‘intuitively’ and then invent reasons to explain our choice. Nice to see it approached from the neuroscience perspective, and getting somewhere in nailing down the sequence of brain activity is exciting. But for all those people who are reacting to the philosophical issue, well, I think you’re late to the bus.

  21. Sonny Alvarez
    May 1, 2011

    Can there be any approaches to connect with this web site with no opt-in into the RSS? I don’t know the reason however I can’t have the RSS filled with the reader though I can read it from the chrome.

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