When Your Brain Fights Itself

Ever forget to drop off dry cleaning on the way to work?

This minor error of memory may be evidence of two competing parts of the brain, one that harbors habits, and another involved in learning.

Driving to work is a habit; going to the dry cleaner is a comparatively novel task.

Dr. Christopher J. Pittenger, assistant professor of psychiatry at Yale, calls this symbolic lapse the "dry cleaning effect."

The whimsical label encompasses two opposing brain systems that could lead to new understanding of obsessive compulsive disorder, drug addiction, and other disorders.

Pittenger and colleagues have demonstrated how these systems work in a study published in Proceedings of the National Academy of Science.

Pittenger, along with Yale researchers Anni S. Lee and Ronald S. Duman showed how mice respond to changes in the murine habit and spatial learning centers in their brains.

The striatum, in the middle of the brain, stores habits and acts like an autopilot. The hippocampus, a smaller structure beneath the striatum, handles new challenges.

"There are two processes to navigate through the world, literally and metaphorically," Pittenger said.

"I'm interested in things that we do automatically," he said. This automatic behavior is reflected in driving to work, versus driving somewhere strange, he said.

"I cannot remember to drop off the dry cleaning. It takes extra effort to get off autopilot," he said.

In this case, "autopilot" is the striatum guiding you to work or home, to the degree that when you arrive, you cannot remember the trip. Other examples ate walking, talking, riding a bicycle, using utensils, and other actions we accomplish without conscious thought.

The hippocampus comes into play when the brain is required to use spatial information in a new way, Pittenger said. Finding your way out of a forest with a compass is a job for the hippocampus.

Both systems function simultaneously.

Pittenger and colleagues presented mice with a pool of water containing a platform. The mice can be trained to find the platform, which becomes a habit encoded in the striatum.

When the striatum was disrupted, the mice lost their ability to quickly find the platform. However, the same mice improved on tasks involving spatial learning.

Conversely, when the hippocampus was disrupted, the mice could not navigate as well, but learned "landmark tasks," like the location of the platform, more quickly.

Pittenger said that obsessive compulsive disorder, some aspects of autism, and substance abuse, could be habit learning gone wrong.

Other problems might result when the striatum and hippocampus diverge. Alzheimer's disease rapidly damages the hippocampus, which is why patients often fall back on ingrained behaviors, he said.

"If the autopilot system is destructive, a novel system must be brought online," he said. For example, OCD is sometimes treated with cognitive behavioral therapy that helps patients recognize and change destructive "autopilot" thoughts.

"If we could understand these systems better, perhaps we could develop new tools to treat negative habits," Pittenger said.