David Jangraw

Probing Visual Decision-Making with TMS

Indecision-Making: Testing a Spatiotemporal Map of Visual Decision-Making with Transcranial Magnetic Stimulation

When you see something approaching from across the street, you’ll react very differently if it’s your mother, your boss, or a bear.  Visual decision-making is the process that makes this possible: identifying an image and acting on that information.  It’s obviously very important, and we use it all the time.  When people can no longer make visual decisions (for example, in cases of dementia and visual agnosia), it’s extremely debilitating.  If we know more about when and where in the brain visual decision-making takes place, it will be a great first step to learning how to fix it when it fails.
Previous members of the LIINC lab have used EEG (the electrode caps that measure “brain waves”) and fMRI (measurements of blood flow in the brain believed to give a 3-D picture of brain activity) to create a spatiotemporal map (where and when) of activity in your brain when you make a visual decision.  But as you may have heard, “correlation does not imply causality.”  We know that this activity happens with visual decision-making, but we don’t know that it is necessary for someone to make a visual decision.   That’s where Transcranial Magnetic Stimulation (TMS) comes in.
TMS is, essentially, a big magnet.  When we put the magnet next to the scalp and discharge it very quickly, it creates a tiny electric current in the brain: all the neurons just under the magnet fire at once.  The effect is not specific enough that we could make someone smell brownies or hear music, but what we can do is disrupt, for a very short amount of time, whatever processing was going on in that tiny part of the brain.
So the idea is this: we think that area X is important for deciding what an image is 320ms after you see it.  So we stimulate X with TMS 300ms after you see an image.  If you get worse (or better) at deciding what the image is, we know we were right!

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