For those who suffer with the debilitating symptoms of Parkinson's disease, Deep Brain Stimulation offers relief from the tremors and rigidity that can't be controlled by medicine. A particularly troublesome downside, though, is that these patients often exhibit compulsive behaviors that healthy people, and even those taking medication for Parkinson's, can easily manage.
Michael Frank, an assistant professor of psychology and director of the Laboratory for Neural Computation and Cognition at The University of Arizona, and his research colleagues have shed some light on how DBS interferes with the brain's innate ability to deliberate on complicated decisions. Their results are published in the current (Oct. 26) issue of the journal Science.
A recent episode of The Bionic Woman featured people operating under orders from neural implants controlled by terrorists. These Parkinson's patients are behaving differently due to implants. Okay, the connection here is weak. The TV show plot assumes technology that is probably decades in the future.
The electronic implants for Parkinson's mess up the function of the brain's subthalamic nucleus (STN) and that probably causes greater impulsiveness.
DBS implants affect the region of the brain called the subthalamic nucleus (STN), which also modulates decision-making.
"This particular area of the brain is needed for what's called a 'hold-your-horses' signal," Frank said. "When you're making a difficult choice, with a conflict between two or more options, an adaptive response for your system to do is to say 'Hold on for a second. I need to take a little more time to figure out which is the best option.'"
We know that people differ greatly in ability to inhibit impulsive desires to carry out various acts. Do naturally occurring variations in the STN cause the naturally occurring variations in impulsiveness?
The STN, he said, detects conflict between two or more choices and reacts by sending a neural signal to temporarily prevent the selection of any response. It's this response that DBS seems to interrupt. DBS acts much like a lesion on the subthalamic nucleus. Frank's hypothesis predicted that DBS would negate the "hold-your-horses" response to high-conflict choices. Surprisingly, it actually sped up the decision-making process, a signature, he said, indicated of impulsive decision making.
Drugs used to treat Parkinson's also cause behavioral problems, but of a different sort. The Parkinson's drugs appear to prevent learning from negative experiences. Hey, what if some people who aren't even on Parkinson's drugs have a limited ability to learn from negative experiences? That might explain self-destructive behaviors that plague some people.
The tendency toward impulsive behavior in Parkinson's patients is well-documented but only dimly understood. How is the STN involved in decision-making and why should things go awry when you stimulate it"
For those taking them, medications did not slow down decision-making conflict. Regardless of whether these patients are on or off medication, for the purposes of the experiment they looked like healthy people or people who are off DBS.
But what Frank found was that medications prevent people from learning from negative outcomes of their choices. That could be one explanation for why patients develop gambling habits. If you learn from the positive outcomes instead of the negative, it could cause you to become a gambler.
"Whereas the DBS had no effect on positive v. negative learning, but it had an effect on your ability to 'hold your horses,' so it was a dissociation between two treatments which we think reveal different mechanisms of the circuit of the brain that we're interested in.
Know anyone who can't learn from their mistakes? Maybe they've got naturally occurring versions of negative outcomes learning disability.
|Share |||Randall Parker, 2007 October 27 11:28 PM Brain Disorder Repair|