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Substantia Nigra Shows Role in Reinforcement Learning

Neurons in region behaved at different rates during learning task with Parkinson's patients

THURSDAY, March 26 (HealthDay News) -- Neurons in the substantia nigra appear to play a key role in human reinforcement learning, according to research published online March 13 in Science.

Kareem A. Zaghloul, M.D., Ph.D., of the University of Pennsylvania in Philadelphia, and colleagues analyzed data from 10 Parkinson's disease patients who were undergoing deep brain stimulation surgery of the subthalamic nucleus. The researchers recorded substantia nigra neuronal activity while patients participated in a learning task by choosing from a red or blue deck of cards on a computer screen, one of which yielded a noticeably higher reward rate.

The rate with which subjects chose from the higher-probability cards rose from 52.5 percent to 70 percent during the experiment, the investigators found. The substantia nigra neurons showed higher firing rates after unexpected gains than unexpected losses. After expected gains and losses, these differences were not observed, the researchers report.

"Our results show that differences in human substantia nigra responses to positive and negative feedback are mainly driven by unexpected outcomes, with no significant differences in neural activity for outcomes that are anticipated according to our model. By responding to unexpected financial rewards, these putatively dopaminergic cells encode information that probably helps participants maximize reward in the probabilistic learning task," the authors write.

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