Final answer:
The brain region associated with substance addiction is the Nucleus accumbens, which is involved in dopamine release and reinforcement of drug-taking behavior as part of the brain's reward circuit.
Step-by-step explanation:
The brain region that is associated with substance addiction is D) Nucleus accumbens. This region has been shown to play a major role in the reward circuit of the brain—it is involved in the release of dopamine, which is a neurotransmitter that mediates pleasure in the brain. Dopamine action in the nucleus accumbens is a significant component of the addictive processes since drugs of abuse typically cause an increased release of dopamine, leading to the reinforcement of drug-taking behavior.
Animal research, particularly studies on male rats, supports that the nucleus accumbens segregates the reward from the motivation aspects of behaviors like substance addiction. Additionally, the limbic system, which includes the amygdala, hippocampus, and cingulate gyrus, is connected to the nucleus accumbens, further influencing emotional responses and addictive behaviors.