As an animal is rewarded for learning new behavior, changes occur in the neurons of its basal ganglia. New scanning methods show that this deep section of the brain lights up when we develop and express sequential motor acts, and also in response to rewards. With the new ability for researchers to see the brain's electrical activity while learning is in progress, they can actually see patterns of activity change permanently after learning takes place. It takes many repetitions, often reinforced with positive feedback, before an action or series of actions become a habit. Strong positive or negative motivators help develop or break habits.
Positive feedback works better than negative.
The system is so sensitive that researchers have seen nerve cells fire in response to a single word, evoking a craving long after a habit has been kicked. Negative feedback, like feeling sick after eating or drinking something, can nip a bad behavior in the bud. In certain behaviors, like drinking alcohol, consequences such as a hangover occur too long after the original binge to do much good as a deterrent. Many receptors are housed in the basal ganglia, which draw neurotransmitters such as dopamine like a magnet. And like a strong magnet, these receptors don't easily let things go.