But recent studies have shown that this dopamine-related learning function is not quite so simple. Humans seem to learn from both reward and punishment. Randall C. O’Reilly of the University of Colorado at Boulder, says that a subset of neurons in the basal ganglia actually become more active with the depleted dopamine transmission produced by punishment.

“We showed that Parkinson’s patients learned better than age-matched controls from negative feedback because this type of learning depends on a subset of neurons that become more active with less dopamine,” O’Reilly says. “Interestingly, this pattern reversed when these patients were given their medication, causing them to learn better from positive feedback.”

Given the complex circuitry of the basal ganglia, research has suggested that they also are a coordination system. Patients with Parkinson’s disease have difficulty coordinating not only movements but more complex cognitive tasks.

“The basal ganglia help you focus,” Frank says. “Think of multiplying 42 times 17. It’s the kind of information you can manipulate in your head but you have to break the problem into parts.”

It is likely that the dopamine released in the basal ganglia system communicates with the brain areas in the prefrontal cortex to allow people to pay attention to critical tasks, ignore distracting information, and update only the most relevant task information in working memory during problem-solving tasks.

The Force of Habit

Neurotransmitters released in the striatum communicate with the learning centers in prefrontal cortex. These neurotransmitters can encourage repeat performances of behaviors and lead to the creation of habits.

Graybiel’s group trains rats on maze tasks and records the firings of groups of neurons in the striatum as the rats learn, forget, and then relearn the task. “Nerve cells are interested in everything,” says Graybiel. “But as rats get good at running the maze, lots of cells in motor striatum tend to fire at the beginning and the end of the run instead of the whole thing. This network in the basal ganglia has ‘chunked’ the behavior.”

Chunking, at its simplest, is the organization of information into specific associated groupings. Graybiel hypothesizes that the basal ganglia system helps the cortex to chunk learning into habits and routines to help the brain more quickly access stored information.

Graybiel and colleagues also found a group of nerve cells in the striatum that are not firing in the same way as the others. “These nerve cells don’t care about the [maze] task at all,” she says. “And yet, there is some electrical activity in those cells that shuts down when the animal learns the task.”

She hypothesizes that these cells work in an attenuating manner by helping the brain tune out information that is not critical to the task at hand: “Perhaps these neurons turn down the noise so you get this beautiful set of expert neurons that know exactly what to do. After all, when you get in the car and press the accelerator, your whole body knows what to do without thinking. It’s a well-oiled procedure that effortlessly comes out of your behavioral repertoire.”

Psychiatric Disorders and Addiction

The basal ganglia are involved not only with Parkinson’s disease but also an array of psychiatric and addiction disorders. Neuroimaging studies have shown abnormal activation of the striatum and other areas of the basal ganglia in patients with schizophrenia, attention-deficit/hyperactivity disorder (ADHD), Tourette’s syndrome, obsessive-compulsive disorder (OCD), and anorexia nervosa, as well as drug addiction.

O’Reilly and Frank have recently started looking at the basal ganglia in learning in patients with ADHD and OCD. Their research has shown that patients with ADHD, who generally show an overall decrease of dopamine in the basal ganglia, show not only impaired learning with positive feedback but also coordination deficits.