Move over, hippocampus. The basal ganglia, a group of interconnected brain areas located deep in the cerebral cortex, have proved to be at work in learning, the formation of good and bad habits, and some psychiatric and addictive disorders.
Scientists have found that the neurotransmitter dopamine, already linked to the basal ganglia in movement disorders, also is important in learning via reward and punishment, as well as in disorders including schizophrenia and attention-deficit/hyperactivity disorder. This new understanding of how the basal ganglia work has revealed possible avenues for treatment of these and other disorders.
Moving Beyond Movement
Historically, the basal ganglia were thought to be mainly involved with aspects of motor control. “Patients with damage to the basal ganglia often have deficits in movement,” says Michael Frank, a neuroscientist at the University of Arizona. “The most obvious are tremors in patients with Parkinson’s disease.”
Earlier studies of Parkinson’s disease showed that, in patients with the disorder, dopamine-producing neurons in the basal ganglia area die, resulting in less dopamine transmission.
Thanks in part to more sophisticated neuroimaging techniques, researchers have found that the basal ganglia are active in far more than movement. “Although no one found gross physical lesions in people with obsessive-compulsive disorder or schizophrenia, often the basal ganglia were implicated by abnormal metabolic activity in the region,” says Ann Graybiel, a leading researcher in the function of basal ganglia at the Massachusetts Institute of Technology. “And now we’re finding that there’s razzle-dazzle plasticity in the basal ganglia during learning.”
Reward, Punishment, and Focus
Recent studies by numerous researchers show that the basal ganglia facilitate learning, with the neurotransmitter dopamine important to the process. One way that these behavioral routines are encoded is by the processing of reward information.
Wolfram Schultz, a principal research fellow at the University of Cambridge in England, studies how the brain processes such information. “When something is really good, you go back for it again,” he says. “One of the definitions of reward is that it is a learning function, that it can increase a particular behavior.”