Treatments

The Biology Of Dithering

Pile of remote controls. i i

hide captionEven with 1,001 channels, it can feel like nothing's on TV.

iStockphoto.com
Pile of remote controls.

Even with 1,001 channels, it can feel like nothing's on TV.

iStockphoto.com

If you've ever felt so conflicted by choice - hundreds of TV channels, pension funds, brands of cereal - that you couldn't decide, you've experienced the well established tendency that psychologists call the "default bias." That translates to, "When in doubt, do nothing."

A new study by grad student Stephen Fleming, of University College London, has looked into the biology behind that thought process. His results suggest that the decision to deviate or not from the status quo may hinge on some of the same neural pathways that keep a Parkinson's patient frozen in place.

Fleming's study was built around a simple video game that required volunteers to make the sort of quick judgement calls that a line judge in a tennis match has to make.

With their heads inside an MRI brain scanner and one finger on a computer mouse, the volunteers stared at a virtual tennis court and watched little "balls" land either "in" or "outside" the backcourt lines. After each ball landed, the computer would randomly call the ball "in" or "out." The volunteers then had just a few seconds to either agree or disagree with the computerized judge, and signal that decision with a click.

The results: When the balls landed close to the line, the volunteers deferred much more often to the computer, though they knew its judgements were random. In those cases, the volunteers were often wrong.

When the calls were very tough and the volunteers acted against the computer's decision, Fleming and his colleagues noted that two particular parts of the brain known as the "subthalmic nuclei," located deep within the cortex, were recruited to help make the decision.

"We found that blood flow around this region increased when you had a difficult decision to make and you successfully rejected the default option," Fleming says.

Here's the cool part: It's the same region that some doctors are hitting with "deep brain stimulation," a treatment that's enabling some Parkinson's patients overcome the rigidity and walking problems that are a part of that illness.This might not be a coincidence, Fleming suggests.

"One of the central problems that occurs in Parkinson's is that you can't initiate an action," he says. "So, once you've started moving you're okay; it's the getting going that's the problem. What is interesting is that when you disrupt this particular structure, the subthalmic structure, with deep brain stimulation, you can alleviate that symptom."

Fleming and others theorize that the subthalmic nuclei might act a bit like "your foot on the brake of the car," helping to keep impulsivity and inaction in balance. The cortex and the parts of the brain involved in controlling movement are in constant communication about potential options, he says. In decision making, "the sublthalmic nucleus could potentially play the roll of easing in and easing out of the brake on the eventual action we take."

Read the full study here, published this week in the Proceedings of the National Academy of Sciences.

Of course, in the real world choices of the cereal aisle, factors like shelf placement, coupons, and the cost of of your last dental bill can complicate basic decisions even further, Fleming says. Ad folks use some of those factors to nudge your decisions in their favor.

The next time you muster the gumption to actively decline the extra insurance option at the car rental counter, think of your subthalmic nuclei, and smile.

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