Neurons that are 'master controller' of habits identified

Scientists have identified a type of neuron deep inside the brain that serves as a "master controller" of habits, and can be targeted with drugs to help overcome addictions or compulsive behaviour in humans.
The team found that habit formation boosts the activity of this influential cell, and that shutting it down with a drug is enough to break habits in sugar-seeking mice.
"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, associate professor at the Duke University Medical Centre in the US.

"We find that this cell is a master controller of habitual behaviour, and it appears to do this by re- orchestrating the message sent by the outgoing neurons," said Calakos.
The findings, published in the journal eLife, may point towards new treatments for addiction or compulsive behaviour in humans.
The team got their first glimpse into the neurological underpinnings of habit in a 2016 study that explored how habits can leave enduring marks on the brain.

The team 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, and 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 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.
In the current 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.
To test whether FSIs are truly the conductors of this cellular orchestra when it comes to habit, a graduate student in Calakos' lab, Justin O'Hare led the effort to take a closer look at 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, and found that the stop and go pathways reverted to their pre-habit brain activity patterns, and the habit behaviour disappeared.

"Some harmful behaviours 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," he said.