Final answer:
The brain structure involved with addiction is the nucleus accumbens in the limbic system. It is responsible for processing reward and reinforcing behaviors, and is associated with the release of dopamine.
Step-by-step explanation:
A brain structure that appears to be involved with addiction is the nucleus accumbens. Research has shown that the nucleus accumbens, part of the limbic system, plays a significant role in the reward circuitry of the brain. It is associated with the neurotransmitter dopamine, which is critical for feeling pleasure. The nucleus accumbens gets activated by rewarding stimuli, including addictive drugs, which increase dopamine release and binding in this region. Over time, with repeated drug exposure, the number of dopamine receptors may be reduced in addicted individuals, as demonstrated by PET scans comparing the brains of addicted versus non-addicted individuals. This reduction can lead to an impaired reward system, contributing to the compulsive nature of addiction.