For methods, the experimenters used 11 subjects. The subjects sat in front of 3 buttons: Left button (LB), middle button (MB), and right button (RB). A subject was cued to move his or her hand to MB, and sometimes, a second cue would show up to correct them to either go left or right, which was chosen at random. The TMS had to be pulsed at a specific time period so that the subject could exhibit blindsight behavior. The TMS pulse caused the correction speed to decrease, which suggests the existence of an efference copy. This is a weird concept--a theoretical construct. Efference copy allows people to predict the effect of their movements. It enables a person to know the difference between actual movement and desired movement while the person moves. The action potentials for the movement don't have to go through an entire neural pathway, so it's like a shortcut, which is why in the experiment, the time taken for the subject to realize he or she have to correct his or her hand direction usually was lower than the amount of time the subject took to process the movement towards MB.
- Fun fact: Have you ever tried tickling yourself? Most people are incapable of tickling themselves. It's a strange phenomenon caused by efference copy.
The study showed that TMS blocks conscious perception of the object placed on the blind side. Subjects of the trial claimed that they could perceive color spheres. But fortunately, TMS only INDUCED the blindsight behavior, so blind sight was not caused by injury or trauma. This reminds me of a kind of stimulation I've mentioned in a previous post: cTBS, a stimulation capable of creating virtual lesions. Crazy stuff, right?
Until my next adventure!
References:
- Christensen, M.S.; Kirstiansen, L.; Rowe, J.B.; Nielsen, J.B. Action-blindsight in healthy subjects after transcranial magnetic stimulation. PNAS. 2007, 105, 1353-57.
- Wikipedia - Efference copy
That's really cool! If a motion correction signal doesn't go through an entire neural pathway, what kind of pathway does it travel?
ReplyDeleteIt still goes through a neural pathway, but a shorter one. To my understanding, efference copies use the correction stimulus to generate a more optimal and less time-consuming neural pathway.
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