How Your Brain Forms a Habit
You wake up. Brush your teeth. Make caffeine. Dress yourself. Dress kids. Pack a bag. And you’re out the door.
Our days are filled with these small routines, made up of habits so rote we barely give them any thought. But we didn’t come out of the womb knowing how to do these things. How do they get so encoded they become almost involuntary?
A new study breaks it down for us. While we may think of each of these actions as a single task, they are usually made up of many smaller actions. When you brush your teeth, you must first pick up your toothbrush, squeeze toothpaste onto it, lift the brush to your mouth, then brush — probably according to your own little pattern of certain teeth first. This process of grouping these tiny, individual behaviors together into a single routine is known as “chunking,” but little is known about how the brain does it, only that it does.
But now, MIT neuroscientists have found that certain neurons in the brain are responsible for marking the beginning and end of these chunked units of behavior. These neurons, located in a brain region highly involved in habit formation, fire at the outset of a learned routine, go quiet while it is carried out, then fire again once the routine has ended, almost like pressing play on a video snippet, and then pressing stop.
These firings appear to be important for initiating a routine and then notifying the brain once it is complete, says Ann Graybiel, a member of the McGovern Institute for Brain Research and the senior author of the study.
The researchers trained rats to press two levers in a particular sequence, for example, 1-2-2 or 2-1-2. The rats had to figure out what the correct sequence was, and if they did, they received a chocolate milk reward. It took several weeks for them to learn the task, and as they became more accurate, the researchers saw the same beginning-and-end firing patterns develop in the striatum, a brain region associated with facilitating voluntary movement, among other functions.
Because each rat learned a different sequence, the researchers could rule out the possibility that the patterns of firing neurons corresponded to control of physical movement.
“I think this more or less proves that the development of bracketing patterns serves to package up a behavior that the brain — and the animals — consider valuable and worth keeping in their repertoire. It really is a high-level signal that helps to release that habit, and we think the end signal says the routine has been done,” Graybiel says.