The reward circuit, which produces feelings of gratification and pleasure, can be activated naturally by enjoyable activities and physical exercise, or artificially by drugs. Dopamine, a neurotransmitter naturally produced in the brain, plays a key role in the function of the reward circuit and in modifying mental and physical activity. Brain dopamine activity may become abnormally low because of blockage or absence of receptors that carry dopamine into target cells in the brain, low production of dopamine, accelerated breakdown of dopamine, and physical breakdown of the brain. Dopamine insufficiency can result in a wide range of difficulties, including loss of motor control, poor memory, attention deficit, and depression.
Drug addicts have fewer dopamine receptors than normal subjects, resulting in low dopamine activity.
There are no differences. The upper PET scans show where the radiotracer C-11 raclopride binds to dopamine receptors. These images show that obese subjects have fewer dopamine receptors than control subjects. The Brookhaven scientists measured the number of dopamine receptors in the brains of ten severely obese individuals and ten normal controls. The PET camera picks up the radioactive signal of the tracer and shows where it is bound to dopamine receptors in the brain.