William James famously wrote “Ninety-nine hundredths of our activity is purely automatic. All of our life is nothing but a mass of habits.”

James, according to Jonah Lehrer, “was pointing out that, though we give habits little thought, they define our lives: how much we eat, save or spend, how often we trek to the gym and what we say to our kids each night.”

But habits are not hard-wired into the brain at birth, they develop over time. What if habits were simply an extreme form of learning? After all, habits let us reserve brainpower for things that can't be predicted in advance. This would conserve brain power for the things we need to think about and relegate the routine nature of tasks.

Lehrer reports with some interesting findings towards this theory:

In a new paper, the neuroscientist Joe Z. Tsien and colleagues at Georgia Health Sciences University describe a mutant strain of mice that were incapable of developing new habits. While ordinary mice quickly developed the habit of pressing a lever to get a food pellet (leading to overeating), the mutant mice stopped pressing the lever as soon as they felt full.

These mice were missing a protein known as an NMDA receptor on their dopamine neurons. Normally, these receptors help to generate a big electrical response when an animal is repeatedly exposed to a rewarding cue, such as a food pellet. According to Mr. Tsien's data, this specific response is what transforms ordinary learning into an automatic behavior. It doesn't matter if we're learning to overeat or to spray Febreze. That big signal from the NMDA receptor makes the difference.

This isn't the first time that Mr. Tsien has tinkered with NMDA receptors. A few years ago, he created a mouse strain with too much of the receptor and created a freakishly smart rodent—Mr. Tsien nicknamed it Doogie—that could learn and remember far better than a normal mouse. He has also showed that younger brains have significantly more of this receptor, which is why they absorb new information and acquire new routines so much more rapidly.

Still Curious? Read The Power of Habit.