Graybiel suspects, however, that the more fine-tuning aspects of physical habits are accomplished elsewhere in the brain. The process of walking, for instance, involves a series of movements, not just an isolated lifting or lowering of a foot. When we repeat a behavior, physiological changes may occur not only in the parts of the brain responsible for motor control but also in the parts that deal with more cognitive functions. The basal ganglia is the only place in the brain to deal with both physical and cognitive actions simultaneously, leading researchers to speculate that the way we program movements and the way we program thoughts may be deeply related. When animals see a light flash or hear a beep when they get something to drink, they come to associate the light or sound with quenching their thirst.
Researchers can see physical changes in their brains as the habit forms.
The neurons in the striatum actually change what they respond to. The brain changes when you pick up a simple habit. While nerve impulses travel at lightning speed, genes take a little longer to change, but they too change in response to stimuli. But because brains are as individualized as our fingerprints, no two brains have an identical response to an identical stimulus. While it may take one person one week to develop a habit, good or bad, it may take another person considerably more time.