THURSDAY, Nov. 4 (HealthDayNews) -- A study of Parkinson's disease patients has led to new insights into how the brain responds to "carrot and stick" learning approaches.

At the same time, the study results may lead to more effective ways to treat Parkinson's and other disorders that involve problems with dopamine, a brain chemical linked to feelings of pleasure and reward.

The research appears in the Nov. 5 issue of Science.

Individuals with Parkinson's have abnormally low levels of dopamine in the basal ganglia section of the brain. This abnormality causes the tremors and other motor impairments associated with the disease.

At the same time, Parkinson's medications that raise dopamine levels frequently produce learning and memory problems in people, the study authors said.

Michael J. Frank, lead author of the study, constructed a model to see how interacting brain regions might affect each other.

"The upshot of the model was that it wasn't really the raw level of dopamine as much as the dynamic range that mattered, the ability of the dopamine system to change both up and down," explained Frank, a doctoral candidate in cognitive neuroscience and psychology at the University of Colorado.

Previous research with monkeys had shown that dopamine levels went up when the animals were rewarded for doing a learning task correctly. When they made a mistake, dopamine levels decreased.

"What the model suggested was that both increases and decreases are important and that by giving patients medication, the medication might be restricting those dopamine levels to always be high," Frank said.

Frank emphasized that he was not suggesting that Parkinson's patients stop taking their medications. "This is just a window into how the system works," he said.

Using his model as a foundation, Frank theorized that Parkinson's patients on medications would be able to learn from their successes but not from their mistakes. His reasoning: When someone successfully completes a task or solves a problem, dopamine levels rise. But the levels drop when a person is unable to complete a task or solve a problem.

To test the theory, Frank and a colleague put 30 Parkinson's patients and 19 healthy senior citizens through a series of learning tasks. The Parkinson's patients stopped taking their regular dopamine medication 18 hours prior to the second task.

Frank said his theory proved correct. Parkinson's patients who stopped their medication were able to learn from their mistakes because dopamine returned to typically normal levels. When the Parkinson's patients restarted their medication, the reverse was true: They learned better from positive feedback and less well from negative feedback than the control group because of the dopamine fluctuations.

The finding has no immediate implication for people with Parkinson's. But it does give a direction for future research, Frank said.

"Eventually, we can figure out how to better design medications that are more likely to have a larger dynamic range," he said. "Basically, it gives us a window into how dopamine is involved in learning."

There may also be implications for other diseases such as schizophrenia and addiction, which involve dopamine dysfunction, Frank said.

"Just understanding from a more basic science perspective how the brain is doing, it might lead to eventually tailoring treatments for those disorders," he said. "Psychiatrists and pharmacological companies were designing medications from the bottom-up perspective. There wasn't enough theory to guide what chemicals we needed. Potentially, from that basic science we'll eventually be able to use a systems level approach."

More information

For more on Parkinson's disease, visit the National Parkinson Foundation.



SOURCES: Michael J. Frank, doctoral candidate in cognitive neuroscience and psychology, department of psychology and Center for Neuroscience, University of Colorado at Boulder; Nov. 5, 2004, Science

Last Updated: Nov-04-2004