In a lab at MIT, a rat enters a T-shaped maze, hears a tone, and runs down the left arm towards a piece of chocolate. It’s a habit. The rat has done the same thing over so many days that once it hears the tone, it’ll run in the same direction even if there’s no chocolate to be found. Humans are driven by similar habits. Every morning, I hear my alarm go off, put some clothes on, and shamble into the kitchen to brew some coffee.
Habits, by their very nature, seem permanent, stable, automatic. But they are not, and the MIT rat tells us why. Earlier, Kyle Smith had added a light-sensitive protein to one small part of its brain – the infralimbic cortex (ILC). This addition allows Smith to silence the neurons in this one area with a flash of yellow light, delivered to the rat’s brain via an optic fibre. The light flashes for just three seconds, and the habit disappears. The rat hears the tone, but no longer heads down the chocolate arm.
The experiment shows that even though habits seem automatic, they still depend on ongoing supervision from the ILC and possibly other parts of the brain. They’re ingrained and durable, but subject to second-by-second control. And they can be disrupted in surprisingly quick and simple ways.
“We were all stunned by how immediate and on-line these effects really are,” says Smith. “Changing the activity of this small cortex area could profoundly change how habitual behaviour was, in a matter of seconds.”
By cutting out bits of a rodent’s brain, or inactivating them with chemicals, other scientists had already identified parts of the brain, including the ILC, that are important for habits. But these are somewhat clumsy methods. Smith’s team wanted some more refined, something that could inactivate the ILC on demand for short bursts of time.