Habit Formation Linked to 'Gateway' to Brain Cells

A new study has revealed that key receptors on brain cells that function like 'gateways' are essential to enable habit formation.

Research showed that NMDA receptors on dopamine neurons in the brain's basal ganglia function like gateways to the brain cells, letting in electrically charged ions to increase the activity and communication of neurons.

Their pivotal role reminded neuroscientist Dr. Lei Phillip Wang of a computer's central processing unit.

"The NMDA receptor is a commander, which is why it's called a master switch for brain cell connectivity," said Wang, the study's first author.

To determine their role in habit formation, GHSU researchers used a genetic trick to selectively disable the NMDA receptors on dopamine neurons and found, for example, mice could be trained to push a lever for food without it becoming an automatic response.

Dopamine is a chemical that helps brain cells in communication.

If they were full, they would not push the lever. But just as humans cannot refrain from flipping a light switch during a power outage, satiated mice with receptors could not pass up the lever.

When they compared the firing of the dopamine neurons in regular versus the mutant mouse, they found a dramatic spike in response to a cue that signals food in the normal mouse and a significantly dampened one in the mutant, Wang said.

"We think this reduced response is probably sufficient for other types of learning, but not for habit learning," he said.

The finding that the receptors are critical to turning learned behaviour into a habit provides new direction for therapy to better treat diseases such as Parkinson's, which in addition to the hallmark shaking, causes the loss of some old habits and impedes the ability to make new ones.

It also opens the door to speeding up the process of forming good habits and, possibly, selectively removing bad ones such as drug addiction or smoking since the same circuits are seemingly involved in both.

"Dopamine neurons regulate circuits all over the brain but they need to be regulated too," said Dr. Joe Z. Tsien, Co-Director of the Brain and Behavior Discovery Institute at Georgia Health Sciences University.

"The questions become how and whether regulation of dopamine neurons is important. Our study shows it's important and it's through the NMDA receptors," Tsien added.