Deciding to reach out your arm and grab something and physically doing it are very different things, a fascinating new study has shown, and are controlled by two distinct regions of the brain. Researchers found that by directly stimulating a brain region called the parietal cortex, they could give test subjects the strong urge to move various body parts, like arms and lips. An even stronger jolt produced a false belief that they actually had moved. On the flipside of the experiment, when researchers stimulated a different part of the brain, the premotor cortex, the subject jerked or twitched, but wasn’t aware of it. The findings suggest that “we need intention to be aware of what we are doing,” says [study coauthor Angela] Sirigu. The brain’s intention and its prediction of what will result from carrying out that intention create our experience of having moved, she says [ScienceNOW Daily News].
The unusual study took advantage of a common operating room practice. As part of their preparation for surgery, neurosurgeons sometimes electrically stimulate the brains of their patients, who are awake under local anesthetic, to map the brain and minimize surgical complications [ScienceNOW Daily News]. In the case of this new study, published in Science, the patients were undergoing operations for brain tumors, but had agreed to take part in an experiment before the main surgery commenced. In all but one of the seven cases, the cancer was located far from the brain regions being stimulated.
Researchers had previously suspected that the parietal cortex was involved in human volition, but experts note that studying voluntary motion in a neuroscience lab runs into some difficulty. “Volunteers can be asked to choose what action to make, when to make it, or even whether to make it at all,” the neuroscientist Patrick Haggard notes in a commentary accompanying the study. “But these instructions—which amount to ‘Have free will now!’—have something unsatisfactory, even paradoxical, about them,” he notes.
Now, directly stimulating the brain region provided the clearest evidence to date of the parietal cortex’s important role in voluntary action. “Did you move?” a researcher asked a 76-year-old man after lightly zapping a point on his parietal cortex. “No. I had a desire to roll my tongue in my mouth,” he responded. After a stronger pulse to the parietal cortex, a 42-year-old man exclaimed: “My hand, my hand moved” [New Scientist]. Yet the research team detected no signs of movement.
Study coauthor Michel Desmurget says the stronger pulse may have fooled the volunteers because it sent a current through areas that simulate in real time how the movement should unfold if the original intention were actually carried out. Normally such computation would be validated by feedback from the premotor cortex which provides information from the body to determine if the hoped for movement has actually happened. “But in the experiment, the parietal cortex is stimulated in isolation — the brain is not getting any error signal, and is relying on the out-dated parietal simulation” [Nature News], he says.
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Image: iStockphoto
May 8th, 2009 at 6:59 pm
Sounds more like the study shows that the parietal cortex receives information (i.e. electrical stimulation) as a feedback mechanism to tell your body it has moved somewhere.
Studies keep showing the brain isn’t as compartmentalized as we think. This is progress, but shocking open parts of the brain to see what happens sounds like hacksaws and hatchets compared to fNMR and DNI technologies that are coming out (it’s possible they used microelectrodes, but the brain is made out of very tiny wiring so even small electrodes may be big in comparison, especially since it sounds like they’re just hitting the surface).
And, honestly, without a fNMR (known as fMRI to not scare people with the N-bomb, the dreaded ‘nuclear’ word) scan showing how the brain was reacting to the stimulation, how do you know other parts of the brain aren’t also reacting – the parietal cortex is NOT in isolation, it in intimately linked to the rest of the brain, so the shock may have carried and bounced off something else.
People with lost limbs can still feel those limbs, sometimes. They can itch and hurt, even though they aren’t there. So, shocking part of the brain and making a person feel like they moved even when they didn’t? Not really shocking news. ;)
May 10th, 2009 at 10:09 pm
Interesting study!
May 12th, 2009 at 9:45 am
Sounds like you are trying to simplify a really complex system when you do NOT know what all the parts are. Much the less how each part functions.
May 12th, 2009 at 11:37 am
The brain is not stimulated with invasive electrodes, nothing goes in. Stimulation is done with something like a little fork with round tips.
The primary purpose is not research. Patients undergo awake surgeries and electrical stimulations allow to determine what can be removed and what cannot if major deficits want to be avoided.
the results you can get with fMRI are not as reliable (the areas that react to movement with fmri are not the areas that respond to electrical stimulations). There are recent papers in nature and neuroimage showing that the bold signal (the one that is recorded by fmri) does not reflect neural activity. When you remove the areas that respond to stimulation you get deficits, when you remove areas that did respond to fmri but not stimulation the patient do fine
You know its specific to the parietal cortex because when you stimulate the areas that are connected with the parietal cortex you don’t get the same response.
Illusory movements may not be shoking news but contrasted with the unconscious movement triggered after premotor stimulation they are a great step forward!
Nobody says stimulation activates only the parietal or premotor cortex. It is because it activates the whole circuit that it is relevant
May 19th, 2009 at 7:33 pm
And now, I will hook you up to my joystick and make you fence each other with car antennas, all the while making you think you’re just sitting there imagining it…
May 26th, 2009 at 5:42 pm
lol!
May 26th, 2009 at 5:43 pm
Did I really lol?
May 26th, 2009 at 5:48 pm
Seriously, Our brain is truly the final frontier – its so fragile and wonderful in design. Makes me wonder why people do crack, crank or whatever horrible drug to destroy their brains potential. Me, I like using mine. I think….