Why does the brain prefer opium to broccoli?
The question of addiction has been put that way by Steven Hyman, a former director of the National Institute of Mental Health. The answer involves the nucleus accumbens, a cluster of nerve cells that lies beneath the cerebral hemispheres. When a human being or other animal performs an action that satisfies a need or fulfills a desire, the neurotransmitter dopamine is released into the nucleus accumbens and produces pleasure. It serves as a signal that the action promotes survival or reproduction, directly or indirectly. The system is called the reward pathway. When we do something that provides this reward, the brain records the experience and we are likely to do it again. Damage to the nucleus accumbens and drugs that block dopamine release in the region make everything less rewarding. In nature, rewards usually come only with effort and after a delay. Addictive drugs provide a shortcut. Each in its own way sets in motion a biological process that results in flooding the nucleus accum
