Developing Intelligence

Action without Intention: Parietal Damage Alters Intention Awareness

Posted by Chris Chatham on August 29, 2008
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Is it possible to form and execute motor intentions without being aware of when those intentions were formed? Precisely this pattern was observed by among (ha!) patients with parietal damage, as reported by Sirigu et al. They showed that patients with parietal damage are specifically impaired at estimating the time they formed the intention to commit a voluntary action, although they are unimpaired on other visual and temporal aspects to the task relative to healthy controls and to patients with cerebellar damage.


The authors argue that intentions formed in prefrontal cortex may be used by parietal areas to create a “foward model” of the anticipated action – matching the consequence of an action against the intention.

Sirigu et al. examined healthy subjects, parietal patients, and cerebellar patients in a simple paraigm: subjects observed a second hand spin around a clock, and were asked to press a button at any point after the first full revolution of the second hand. The paradigm had two conditions: in the “moved” condition, subjects were required to report the location of the second-hand at the time they initiated the movement, and in the “willed” condition, they were required to report the location of the second-hand at the time they formed an intention to move.

Previously this task has shown that intentions to move are estimated to occur some 200-300 miliseconds prior to the estimates of the movement. Estimates of the onset of movement are also quite accurate: they’re not significantly different from the time movements are actually made.

Whereas all subjects (healthy controls, and those with cerebellar or parietal damage) were able to estimate the timing of their movements very reliably, only the parietal patients estimated their movement intentions to have occurred at the moment the movement was made. A possible conclusion is that parietal damage leaves the intentions themselves intact (after all, subjects shouldn’t have responded at all, if they were unable to form intentions), but specifically impairs the maintenance of this intention over time, as indicated by a failure to reliably estimate its onset, and by other work indicating an important role for parietal cortex in motor intentions.

Perhaps parietal cortex is important for these maintenance and anticipatory aspects of movement- and intention-related processing. This clearly squares with the idea that parietal cortex is specialized for maintaining information over time, like the relationships between stimuli and responses and of occluded objects.

However, there are other studies indicating that the presupplementary motor area and the dorsolateral prefrontal cortex may be more involved in the intention-related aspect of motor movement. As discussed previously, Lau et al suggest that activity in the presupplementary motor area represents intentions, as shown by larger functional connectivity between prefrontal and pre-SMA relative to parietal and pre-SMA, but we might expect that simply based on the fact that pre-SMA and dlPFC are closer in cortex. Other work from the same group has shown that TMS to the preSMA distorted movement intention perception backwards in time, and shifted the perceived onset of movement forwards in time. This result seems to show a nonspecific role for preSMA in reporting motor-related activity (an unsurprising finding). Unfortunately, Lau & colleagues did not try TMS over the posterior parietal cortex, which according to the Sirigu et al theory should have selectively shifted the estimation of intentions but not perceptions of movement onset.

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Comments

  1. #1 Andre
    August 30, 2008

    I believe the behavioural task used by Sirigu et al is flawed as a very important demand characteristic is present in the experiment. The same subjects are being asked to report on time of intention in some trials, and time of action in others. This could mean that a distinction is being imposed on them, and rather than reporting on an actual experience of intention (whose existence is not clear to be an “urge” to move)they could be behaving as they believe they are expected to by the experimenters. fMRI, EEG and other techniques used in brain mapping (spatial and temporal) are only as powerful as the experimental design used; dealing with such techniques one should be aware of potential limitations when attempting to draw conclusions from experimental results. I would advise Nikos Logothetis’ excellent piece on Nature in this respect: http://www.nature.com/nature/journal/v453/n7197/abs/nature06976.html

  2. #2 Luci
    August 30, 2008

    Between this test related post and the AX-CPT test post, the phrase ‘mind-numbing boredom’ showed a marked proclivity to occur at regular intervals. This did not result from the erudite Chathamesque presentation of information, but from the wonderment at the generally boring design of the cited tests. What is going on the higher cortical functioning of test designers when devising such daydream-inducing tests? Boredom would appear to induce intention without action. And possibly snoring.

  3. #3 CHCH
    August 30, 2008

    Luci – sorry about the boredom :) I agree, there is a lost art in designing experiments in cognitive science so that they are interesting both to the experts and to the layperson – especially those laypeople who are subjects in the experiment!

    Andre, you have an interesting point, which is (I think) that the patients with parietal damage may have been impaired at making a distinction between intention and action onset, whereas healthy subjects and those with cerebellar damage would not be impaired in this. this would say something rather different about the function of parietal cortex. on the other hand, one of the control tasks was for subject to indicate the location of the clock hand at the time of a “beep” delivered by the computer, so they are not impaired in following instructions more generally. it is possible that they are impaired only at making distinctions between action and intention, but then that would support a conclusion much like Sirigu et al’s…

  4. #4 Andre
    August 31, 2008

    CHCH:

    I typed my post in a hurry, so I’m afraid it might not have been clear. That is not what I meant. What I wanted to say was that I believe the whole behavioural task to be inadequate, i.e., to be devoid of validity. If people performing the task are not actually attending to an “intention to move” then it follows that results and conclusions drawn from this task are unwarranted.

    More concretely, what I propose is that the within-subjects design used is not inocuous. By having people undergo an experiment in which they had to, in different trials, report on the experience of intention and in others, movement, the experimenters might have imposed a distinction (between intention and movement) that might not have otherwise been felt by the subjects.

    Subjects might then have just conformed to this distinction, and performed the experiment according to what they thought they were supposed to do – to report, on movement trials, the time when they moved, and on intention trials, a time prior to this.

    Healthy subjects would have been able to infer this demand characteristic. As for brain-damaged subjects, I don’t know what they would have done. My point is that, to begin with, the task lacks validity and one should not jump at conclusions about intention and action when it isn’t clear that the task engages the first. During this year, I’ve actually conducted 2 experiments to test the validity of this paradigm; as soon as I have a URL for the paper, I’ll post it here.

    @Luci: I agree with you. This is something that is neglected in many behavioural experiments with humans. When you work with animals, they are usually motivated by something like food restriction, being given access to food during the experiment, in a manner contingent to a given task. With humans sometimes financial compensation is offered, but this is

    a) generally symbolic, and thus has a remarkably lower value to the human subject than to the food-deprived experimental animal

    b) offered at the end of the experiment – or even worse, upfront. Human experiments should be designed in a way which engages the subjects’ attention during the experiment, keeping him motivated. Honestly, I believe that frequently human data pertaining to some subjects is hard to interpret because of this reason.

  5. #5 CHHC
    August 31, 2008

    Andre- fascinating. Let me summarize your position to be sure i understand it:

    you propose that demand characteristics in the Libet paradigm might create a distinction (between intention and movement) that patients with parietal (but not cerebellar) damage cannot infer or comply with. The Sirigu conclusion requires verification that the intention (or “W”) condition in the Libet paradigm actually measures intention to move, as opposed to something like “ability to infer demand characteristics and subtle distinctions.”

    If this is an adequate summary, then it seems that my previous point still holds: Sirigu et al show that cerebellar patients can do something parietal patients cannot, and the Sirigu results nonetheless say something about parietal function (though perhaps not what Sirigu et al claim).

    Does your design use the Stetson et al sensory-motor recalibration paradigm in any way? just curious

  6. #6 be?i bir yerde
    November 16, 2008

    My point is that, to begin with, the task lacks validity and one should not jump at conclusions about intention and action when it isn’t clear that the task engages the first.