The Duke University neuroscientists have found a single type of neuron deep within the brain that serves as a controller of habits. These findings help towards new treatments for addiction or compulsive behavior in humans.
The team found that habit formation boosts the activity of this influential cell. That shutting it down with a drug is enough to break habits in sugar-seeking mice. The cell exerts its control through a web of connections to more populous cells that are known to drive habitual behavior.
This cell is a relatively rare cell but one that is very heavily connected to the main neurons that relay the outgoing message for this brain region, said Nicole Calakos, an associate professor of neurology and neurobiology at the Duke University Medical Center. We find that this cell is a master controller of habitual behavior. It appears to do this by the message sent by the outgoing neurons. Trained 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. Despite having had an opportunity to eat all the treats they wanted beforehand. The team then compared the brain activity of mice who had developed a lever-pressing habit with those who hadn’t.
They focused on an area deep within the brain called the Striatum. It 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.
Fast-Spiking Inter neurons
In the study, the team wanted to understand the circuitry that coordinates these various long lasting changes in the brain. They had a hunch that a single type of rare cell in the striatum called the Fast-Spiking Interneuron (FSI) might serve as master conductor of the widespread changes in the outgoing neurons’ activity. The FSI belongs to a class 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 way that fast-spiking interneurons are connected up to the other cells. It could be the one cell that is driving these changes in all of them.
To test whether FSIs are truly the conductors of this cellular orchestra when it comes to habit. The brain activity in lever-pressing mice. He found that forming a habit appeared to make the FSIs more excitable. He then gave the mice a drug that decreases the firing of FSIs. The stop and go pathways reverted to their pre-habit brain activity patterns. And the habit behavior disappeared.
Some harmful behaviors like compulsion and addiction in humans might involve corruption of the normally adaptive habit-learning mechanisms Calakos said. Understanding the neurological mechanisms underlying our habits may inspire new ways to treat these conditions.