EVANSTON, Ill., Aug. 12 (UPI) -- U.S. scientists say they've found some human behavior is controlled by balanced activation of two pathways in the brain using the neurotransmitter dopamine.
Professor James Surmeier and colleagues at Northwestern University say their discovery helps explain Parkinson's disease and drug addiction.
Dopamine "shapes the two main circuits of the brain that control how we choose to act …," said Surmeier, adding both circuits are in the brain's striatum, a region critical for translating thoughts into action. One circuit activates conduct while the other inhibits it.
In drug addiction, Surmeier explained that "dopamine released by drugs leads to abnormal strengthening of the cortical synapses driving the striatal 'go' circuits, while weakening synapses at opposing 'stop' circuits." The result is the compulsive conduct seen in addiction.
In a second experiment, the researchers created an animal model of Parkinson's disease by killing dopamine neurons. When the researchers simulated cortical commands to move, the inhibitory pathway was strengthened and the activation pathway was weakened.
"The study illuminates why Parkinson's patients have trouble performing everyday tasks like reaching across a table to pick up a glass of water when they are thirsty," Surmeier said.
The research is reported in the journal Science.
