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matthew.costello
Starting Member
5 Posts |
 Posted - Jun 28 2007 : 11:21:57 AM
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Hi,
We have been getting bilateral motor activity with our 3T experiments when we code for all left hand responses or all right hand responses. Subjects were using the button box for responses. The task is a task switching paradigm in which subjects must decide whether the presented word is either manmade or natural (taskA) or large or small(taskB). They responded with either a left or right keypress, such that the left could be manmade or large, right natural or small. So each response key had double duty for a response in each category.
I didn't know whether this bilateral motor activation is true activity or if there is some bug somewhere. We wanted to use motor strip laterality as an initial check on the orientation and quality of the activations, so now I am stuck. I didn't know if anyone else found such bilateral motor activation with the 3T button box. I have heard that the keys are very sensitive and so subjects may have had their fingers up throughout, or maybe the opposite finger would be lifted as signfying 'no', etc.
Any advice would be appreciated!
Matt |
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diaz
BIAC Alum
USA
212 Posts |
Posted - Jun 28 2007 : 11:26:45 AM
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are participants responses blocked? That is, do they know on a given run that they will always respond with for example, the right fingers. Or is it the case that on a trial by trial basis there is the possibility of either a left or right finger response.
If the latter is the case, could mental/anticipatory preparations for the response be contributing to bilateral activations?
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Michele T. Diaz, Ph.D.
Associate Director
Brain Imaging and Analysis Center |
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matthew.costello
Starting Member
5 Posts |
Posted - Jun 28 2007 : 11:53:25 AM
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The responses were not blocked, but rather switched from trial to trial with occassional repetitions. So on any given trial, the cue could be 'manmade or natural', or 'small or large', and they would have to push the appropriate button. But participants did know that the left key was for manmade or small, etc - these were assigned at the beginning of the testing session. However, they knew of which task (A or B) to do only one second prior to the onset of the target word - thus the challenge for the task. So it may well be that there were the mental/anticipatory preparations you mention. I had just assumed that motor laterality would nevertheless come through.
We were hoping to use motor laterality as an initial check of the functional images, something we've done in the past.
Thanks for your comments, Michele. |
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jim.voyvodic
BIAC Faculty
138 Posts |
Posted - Jul 13 2007 : 10:51:21 AM
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Hi,
I do left vs right hand motor tasks routinely for mapping the motor cortex in patients (in preperation for brain surgery). Use of eithert hand always activates the motor cortex strongly on the contralateral side and less strongly, but still very significantly, on the ipsilateral side. The motor cortex has strong cross-callosal connections so there is likely direct M1-M1 interaction as well as whatever anticipatory or compensatory effects may enter from other brain regions.
Bottom line is that if you simply ask which side of cortex is active the answer will almost always be both (if you have the SNR to see it), but if you ask which side is more active it will always be contralateral.
Hope that helps.
Jim |
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Bilateral motor activation with 3T button box
