Not Exactly Rocket Science

Blogging on Peer-Reviewed ResearchWhen it comes to the human brain, even the simplest of acts can be counter-intuitive and deceptively complicated. For example, try stretching your arm.

Nerves in the limb send messages back to your brain, but the subjective experience you have of stretching isn’t due to these signals. The feeling that you willed your arm into motion, and the realisation that you moved it at all, are both the result of an area at the back of your brain called the posterior parietal cortex. This region helped to produce the intention to move, and predicted what the movement would feel like, all before you twitched a single muscle.

Michel Desmurget and a team of French neuroscientists arrived at this conclusion by stimulating the brains of seven people with electrodes, while they underwent brain surgery under local anaesthetic. When Desmurget stimulated the parietal cortex, the patients felt a strong desire to move their arms, hands, feet or lips, although they never actually did. Stronger currents cast a powerful illusion, convincing the patients that they had actually moved, even though recordings of electrical activity in their muscles said otherwise. 

But when Desmurget stimulated a different region – the premotor cortex – he found the opposite effect. The patients moved their hands, arms or mouths without realising it. One of them flexed his left wrist, fingers and elbow and rotated his forearm, but was completely unaware of it. When his surgeons asked if he felt anything, he said no. Higher currents evoked stronger movements, but still the patients remained blissfully unaware that their limbs and lips were budging.

These contrasting responses tell us two important things. Firstly, they tell us that our feelings of free will originate (at least partially) in the parietal cortex.  It’s the activity of these neurons that creates a sense that we initiate actions of our own accord. Secondly, they show that the sense of moving doesn’t depend very much on actually doing so – it depends on calculations that are made in the parietal cortex, long before the action itself begins.

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The seven patients in Desmurget’s study were brain cancer patients, who were having their tumours removed. All of them gave consent to have their brains stimulated as part of the operations, something that’s often done beforehand to check that everything’s working and minimise the risk of major complications after the surgery.

Stimulating the brain with electrodes in this way gets around a major problem with studying the idea of “free will” in a laboratory setting. It allows scientists like Desmurget to carefully control their experiments, delivering a very precise input and watching the result. The alternative would be to give volunteers the framework of a task and get them to choose what action to make, when to make it or whether to make it at all. Another neuroscientists, Patrick Haggard, describes these experiments as “unsatisfactory, even paradoxical”, the equivalent of instructing people to “have free will now!”

Electrodes help to bypass that problem, and this isn’t the first time that scientists have used them to the subjective side of movements. In 1991, Itzhak Fried found that delivering an electric jolt to a person’s supplementary motor area (SMA) produced a strong urge to move. But unlike the desires experienced by Desmurget’s patients, these urges felt strong and irrepressible, like they went beyond the patients’ own will. With enough current to the SMA, Fried could trigger actual movements.

Desmurget, on the other hand, could only ever produce the illusion of movement by focusing on the parietal cortex.  And his patients’ descriptions of their experiences made it very clear that they were feeling some sort of internal intention to move, rather than feeling compelled by an external force. Without any prompting from the researchers, they all described their feelings with words such as “will”, “desire” or “wanting to”. One of the patients said, “I felt a desire to lick my lips”, after a low burst of current. With more stimulation, he said “I moved my mouth. I talked. What did I say?”

These results are a good fit with those of previous studies. Research on monkeys suggests that the posterior parietal cortex contains a sort of “map of intentions”, where different areas are dedicated to planning different groups of movements – looking, grasping, reaching, and so on. And in humans, people with parietal cortex damage aren’t aware of their intention to move. They can tell when they start moving, but not when they actually decided to do so.

To Haggard, the SMA and the parietal cortex are two sides of the same coin. All the voluntary actions we do, from kicking a ball to opening a door, eventually pass through the primary motor cortex, the final staging ground where electrical thoughts are converted into muscular deed.

This area receives inputs from two others – the premotor cortex, which governs movements that respond to something in the outside world, and the SMA, which is involved in actions that we make of our own accord. The SMA prepares commands for the actions we undertake. But it also communicates with the parietal cortex, which predicts what it would feel like to carry out those actions and create a sense of ownership over our own movements. 

Dualist philosophers like Descartes believed that the mind and consciousness exist outside the physical world, producing our actions by interacting with the physical meat of our brains. The idea has become commonplace, but it’s challenged by neuroscientific studies like this one, which show that the conscious intention to move emerges from electrical activity in neurons, tangible objects that are all too real.

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Reference: Desmurget, M., Reilly, K., Richard, N., Szathmari, A., Mottolese, C., & Sirigu, A. (2009). Movement Intention After Parietal Cortex Stimulation in Humans Science, 324 (5928), 811-813 DOI: 10.1126/science.1169896Haggard, P. (2009). The Sources of Human Volition Science, 324 (5928), 731-733 DOI: 10.1126/science.1173827

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Comments

  1. #1 working class
    May 7, 2009

    going to try some diy electrical stimulation

  2. #2 Mo
    May 7, 2009

    The findings you describe here are almost exactly the same as those reported by Wilder Penfield in the 1930s. Penfield pioneered this technique of presurgical evaluation, and evoked both movements and the intention to move by electrically stimulating the cortex. The main difference, to my knowledge, is that Penfield did not evoke the illusion of movement.

  3. #3 Nigel
    May 7, 2009

    There seems to be something crucial missing from this story. If they felt the urge, or formed the intention, to move when their parietal cortex was stimulated, why did they not actually do so? Their brain areas are not disconnected are they?

    Apparently, with a stronger current applied to the parietal, they thought they had moved even when they had not. It rather looks as though this is not where intentions to move are formed, but where we register the fact that we have moved, and confabulate a story about having willed it. The trouble with that, however, is that when they actually did move, after premotor cortex was stimulated, they apparently did not register it in their parietal cortex.

    The diagram makes a bit more sense, because it seems to show the intention to move coming from the presupplementary motor area, which appears to be signaling to both the primary motor cortex (to produce the actual movement) and the parietal. I am guessing that the diagram means that the parietal’s job, in this scenario, is to compare afferent input about the actual movement with the signal from the presupplementary area and to conclude, “Ah yes, that was a movement I intended to make” (or if the appropriate signal from the presupplementary area, to conclude that it was an unintentional movement of some sort).

    The trouble with that interpretation, however, is that from the account given it is not apparent that they did any experiments on the presupplementary motor area. Are they relying on other work which implicates that in the formation of intentions?

    Anyway, unless there is some key point missing from the account of what is being done here, these results do not make a whole lot of sense. I am not saying the findings are not real, but it is not at all clear what they mean, and it is almost certainly wrong to interpret them as having located the “seat of the will,” if there is such a thing.

  4. #4 yismith
    May 8, 2009

    Would you please post a full citation of the article for those of us who would like to look at it more in depth?

  5. #5 MM
    May 8, 2009

    That means Matrix can actually be made one day – no actual motion is required to experience living !

  6. #6 Lilian Nattel
    May 8, 2009

    I think it’s fascinating when metaphysics meets neuroscience. We see inside the brain too–that doesn’t mean what we see isn’t real. However the fact that intention and perception and action and awareness of action are distinct–that takes a lot of thinking about.

  7. #7 Daneel
    May 8, 2009

    Yeah! More evidence for determinism.

  8. #8 Ed Yong
    May 8, 2009

    Nigel, the model you describe in the second paragraph of your comment is essentially what I write about at the end of the post and the one suggested by the diagram. That model is more explicitly laid out in the review by Hagger (which I’ve cited above) who looks at both the new data from Desmurget and previous work on the presupplementary motor area. Also, on the basis of this model, I was specifically trying *not* to imply that there was a “seat of will” somewhere in the brain. Which is why the headline, and various summarising sentences, describe the electrodes as producing “feelings of free will” rather than broader statements like “free will produced in the parietal cortex”.

    Also, I caution against reaching too far based on these conclusions. I don’t particularly see anything here that counts as “evidence for determinism” or that “no motion is required to experience living”.

  9. #9 Waylon
    May 8, 2009

    So does this mean that in a few years we can stimulate our brains in such a way to produce a stroking movement of the hand without being aware of it? Because that would sell well in the porn industry. Ooooo….The Stranger :D

  10. #10 Philip
    May 9, 2009

    I’m not sure I understand the challenge being made to dualism here – dualism posits a locus of identity that can will the body to move. Thus, a person is a mind which controls a body. This picture paints a relationship between body and mind, such that the body is the actual vessel of movement, and that a person controls all necessary relations between mind and body necessary to make their body move in the intended manner. This predicts that the brain is something which, when told by the mind, has the ability to feed the body commands – physically – to move. So all the connections between regions of the brain and parts of the body is expected if dualism is true.

    I don’t really know where I stand on philosophy of mind, so it would be great if I could get how this study challenges dualism so I can properly weight it in the debate. Thanks to anyone who explains it to me. :-)

  11. #11 llewelly
    May 10, 2009

    When Desmurget stimulated the parietal cortex, the patients felt a strong desire to move their arms, hands, feet or lips, although they never actually did. Stronger currents cast a powerful illusion, convincing the patients that they had actually moved, even though recordings of electrical activity in their muscles said otherwise.

    But when Desmurget stimulated a different region – the premotor cortex – he found the opposite effect. The patients moved their hands, arms or mouths without realising it. One of them flexed his left wrist, fingers and elbow and rotated his forearm, but was completely unaware of it. When his surgeons asked if he felt anything, he said no. Higher currents evoked stronger movements, but still the patients remained blissfully unaware that their limbs and lips were budging.

    These contrasting responses tell us two important things. Firstly, they tell us that our feelings of free will originate (at least partially) in the parietal cortex.

    Here you conflate ‘desire’ with ‘free will’ . Desires to use addictive drugs, desires invoked by various mental disorders, and many other desires are often perceived as being in opposition to ‘free will’ by nearly everyone I know.

    When I originally read your title, I chuckled and thought ‘feelings of free will artificially induced, ha, how ironic’, but neither the content of your article nor the paper’s abstract supports that interpretation at all. (An interpretation that the word ‘electrically’ in the title does not imply ‘artificially’ fails because all brain activity is electrically induced, so there’s no point in using the modifier ‘electrically’ unless such inducement comes from outside electricity.)

    To support the title of your post, research would need to ask a question something like this: ‘Can electrical stimulation (of external origin) induce feelings of free will?’ rather than ‘desire’, which obviously includes desires most people perceive as being in opposition to free will. I suspect that question will someday be answered with a ‘yes’, but this research does not ask any such question, or any related question.

  12. #12 Anonymous
    May 11, 2009

    Actually, there’s no disagreement between dualism and this study. If intentions originated outside the physical brain, there could still be a region of the brain that responded to those nonphysical intentions and turned them into physical, elctrochemical ones.

  13. #13 Juuso
    May 13, 2009

    As a study this is certainly interesting, but nothing new and certainly not worth the rather ambitious title.

    To begin with this modern and popular thinking “neurological finding x refutes dualism” has been fundamentally misguided. This has been going on for over a century, so no big problems. This has absolutely nothing to do with dualism. In dualism (and not all dualism is of Cartesian kind, nor is Cartesian dualism like i is so commonly presumed to be in modern scientific writings) mind and body (brain) heavily interact. Mind affects and alters brain and vice versa.

    To begin with we are not discussing free will or even “will” or source of “intentionality” (philosophical concept) here. What we have here is study focusing on desires and desires are subconscious. After all, who of us can predict what we will want to do five minutes from now. Desires enter our consciousness and then we modify them, make choices between them, repress them etc.

    Hunger (and thus desire to eat) is generated by body. Drugs affect body and brain and make addict desire for them. Yet no one has claimed these desires like “I want food” create feelings of free will.

    Nor are “intentions” created here. In fact it could be argued that this “parietal cortex” that gets feeded with a lot of these kinds of “high level” process informations acts as one of many translators between body&mind. Thus when it gets these “screwed” shocks it translates them for mind/subconscious where intentions are born. And thus subjects feel these strange, fleeting “wants”. It is all about transmission of information between brain and mind. If signals from either ones are, well, “screwed” results like these are expectable.

    “Also, on the basis of this model, I was specifically trying *not* to imply that there was a “seat of will” somewhere in the brain. Which is why the headline, and various summarising sentences, describe the electrodes as producing “feelings of free will” rather than broader statements like “free will produced in the parietal cortex”.”

    Yes, it is highly unlikely such “seat of will” exists. Knowing plastic nature of brain I’d say it is in fact impossible.

    There are many other regions in brain that if simulated create “needs” or “desires”. Now we’ve added yet another one to list, rather powerful one in fact. But that’s all. This wild chase for “ghost in the machine” thas has gone on for decades haven’t progressed anywhere and will not.

  14. #14 Neuroskeptic
    May 15, 2009

    I write a bit about this study here.

    Mo: You say that Penfield evoked the intention to move. It was my understanding (based on second hand report – I haven’t read his work) that he didn’t think that was possible… are you sure about that?

    You may well be right. And it is rather puzzling that Desmurget et al don’t mention Penfield. I would have thought that, at the very least, Penfield must have stimulated the parietal cortex many times.

  15. Once upon the time, when all children have the chips imputed in their heads just after being born (to help to connect Internet as computers were outdated those days), there were some corporations that decided to use this miracle of technology in some unfair way. Everytime a client go through electric gates entering any shop their prepaired shoplists is messed and their feel the unbeatable need to buy the newest product of XYZ company…

    It’s just my imagination about changing our free will with electrodes. And I hope this won’t ever come true.

  16. #16 E Mondini
    May 24, 2009

    Very interesting and I applaud Yong for publishing this work. I walk away from this more aware than ever of my every move, including typing this comment, but the reading of this begs the question: it appears even the awareness itself is illusory. Clearly, it seems we are not equipped to penetrate this mystery past our own inherited barriers. I can only imagine what Yong must be contemplating after this study.