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Brain cells know which way you'll bet

Neural activity in nucleus accumbens foretells card-game decision making

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2:38pm, February 27, 2012
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SALT LAKE CITY — When it comes to tough financial decisions, people are often clueless. But some cash-savvy nerve cells deep in the brain know what to do. And these cells know the plan seconds before the person actually decides on a course of action, new research shows.

The findings, presented February 25 at the Computational and Systems Neuroscience meeting, may help scientists understand how people make difficult decisions.

Shaun Patel of Massachusetts General Hospital and colleagues enlisted eight people undergoing experimental therapy to alleviate severe depression or obsessive-compulsive disorder that involved implanting electrodes deep into the brain.

During surgery, the electrodes eavesdropped on the behavior of individual nerve cells in an otherwise unreachable area of the brain called the nucleus accumbens. Other places in the brain feed lots of diverse signals to the nucleus accumbens: Information about a person’s emotions, memories and more sophisticated reasoning — key ingredients for decision making — all flow into this area.

While in the operating room, participants played about 250 rounds of a simplified version of the card game “War,” in which two players each receive a card, and the higher card wins. The deck contained only cards numbered 2, 4, 6, 8 and 10 — all spades.

Participants saw a video screen with their card face up next to a face-down opponent’s card. After a short wait, the players pushed one of two buttons to bet either $5 or $20 that they’d beat their opponent. Finally, the face-down card was flipped over, and the participants saw the results of their wager.

Meanwhile, researchers detected 19 nerve cells in the nucleus accumbens that seemed to be involved in the betting. Electrical signals from these cells predicted whether a person would bet high or low. Most surprisingly, this nerve cell pattern was evident about 2.8 seconds before a player pushed a button — a delay so long that it’s “unheard of in neuroscience,” Patel said.

These nerve cells receive information from other brain systems and call the shots fast, before the rest of the brain catches up, Patel said. “The brain is presumably calculating these things before you’re conscious of it.”

For difficult decisions, such as whether to bet high or low on a six of spades, a few key outbursts from this handful of nerve cells might be the deciding factor. 

Neuroscientist Naoshige Uchida of Harvard University cautions that the results are based on the average behavior of a small number of nerve cells. Nonetheless, these kinds of experiments that reveal single nerve cell behavior in human brains hold promise, he says. “I think it’s a fascinating direction to go in.”

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