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Study Explains Puzzling Dopamine Effect AFP November 05, 2004 WASHINGTON: A new medical study helps explain the puzzling effect of dopamine on patients suffering from the degenerative nerve disorder Parkinson's disease, said a report out Thursday. Doctors have been aware that dopamine levels worsen performance in some cognitive tasks while improving performance in others, without knowing why. Parkinson's patients, when off their dopamine-increasing medications, learn better from negative feedback, such as being scolded, the study said. And they learn less from positive feedback, such as being praised, than do healthy people of the same age and intelligence. The study was published in the current issue of the journal Science. "When these same Parkinson's patients take their dopamine medication, they show the reverse pattern, learning better from positive feedback and worse from negative feedback than controls," said the University of Colorado research team. "Dopamine is a brain chemical associated with feelings of pleasure and reward that is thought to contribute to learning through both positive and negative feedback," said the report. "Loss of dopamine leads to the symptoms of Parkinson's. This work may also extend beyond Parkinson's to address the neurobiology of learning from experience: learning that occurs when positive feedback or rewards reinforce behavior and negative feedback causes people to avoid such behavior," it said. The research also identified a group of brain receptors in mice that appear to be responsible for nicotine addiction. "These findings may help scientists find targets for drugs aimed to help smokers kick their habit," said the report. "Nicotinic acetylcholine receptors are expressed in the brain structures thought to be involved in the addiction to smoking. "These receptors, which are embedded in the surfaces of neurons, can be composed of different combinations of subunits ... Mice with a mutation in the 'alpha4' subunit were unusually sensitive to the effects of nicotine." AFP SOURCE: The Australian, Australia http://tinyurl.com/6g3lc * * * ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn