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Single brain cell could hold clue to habits
September 17, 2017, 2:56 pm

Scientists at Duke University in the US have pinpointed a single type of neuron deep within the brain of mice that serves as a ‘master controller’ of habits. The findings could have implications on future treatments for addiction or compulsive behavior in humans.

The team found that habit formation boosts the activity of this influential brain cell, and that shutting it down with a drug was enough to break habits in sugar-seeking mice. Though rare, this cell acts as a master controller of habitual behavior by re-orchestrating the message sent by the outgoing neurons in the brain.

For their study, the team trained otherwise healthy mice to receive a tasty treat every time they pressed a lever. Many mice developed a lever-pressing habit, continuing to press the lever even when it no longer dispensed treats, and despite having had an opportunity to eat all the treats they wanted before-hand.

The team then compared the brain activity of mice which had developed a lever-pressing habit with those who had not. They focused on an area deep within the brain called the striatum, which contains two sets of neural pathways: a ‘go’ pathway, which incites an action, and a ‘stop’ pathway, which inhibits action.

They found that both the go and stop pathways were stronger in habit-driven mice. Habit formation also shifted the relative timing of the two pathways, making the go pathway fire before the stop.

To understand the circuitry that coordinates these various long lasting changes in the brain, the researchers focused on a single type of rare cell in the striatum called the fast-spiking interneuron (FSI).

The FSI belongs to a class of neurons responsible for relaying messages locally between other types of neurons in a particular brain region. Though FSIs make up about only one percent of the cells in the striatum, they grow long branch-like tendrils that link them up to the 95 percent of neurons that trigger the stop and go pathways.

The researchers found that forming a habit appeared to make the FSIs in the mice more excitable. They then gave the mice a drug that decreased the firing of FSIs, and found that the stop and go pathways reverted to their ‘pre-habit’ brain activity patterns, and the habit behavior disappeared.

Since harmful behaviors like compulsion and addiction in humans might involve corruption of the normally adaptive habit-learning mechanisms, understanding the neurological mechanisms underlying our habits could inspire new ways to treat these conditions, said the researchers.

“We firmly believe that to develop new therapies to help people, we need to understand how he brain normally works, and then compare it to what the 'broken' brain looks like," they added.

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