The Neuroscience of Addiction and Reward
The reward circuits in the brain, particularly those in the nucleus accumbens, play an important role in addiction. They encode a number of important information such as amount of reward, expectation of reward, and the delay of reward.
During intoxication, drugs such as nicotine and alcohol cause large bursts of dopamine in the nucleus accumbens that enhance drug-seeking behavior. During withdrawal, however, these bursts of dopamine are attenuated.
What is the Reward Pathway?
The reward pathway is a circuit of brain structures that are activated when we experience something pleasing. This may be something as simple as eating a tasty treat or as complex as having sex.
The most well-known part of the reward pathway is called the mesolimbic dopamine system, which is composed of dopaminergic projections from the VTA to many of the major brain regions involved in encoding and storing memories (amygdala, hippocampus, etc).
This neurotransmitter release, along with other chemicals released by the neurons, is thought to lead to subjective feelings of pleasure and happiness.
The VTA is also the site of dopamine neurons that communicate with the nucleus accumbens, or ventral striatum, another key brain area associated with motivation and reward. When we are experiencing a natural reward or a drug of abuse, these dopamine neurons tell our brains whether the stimulus is rewarding or not.
How Does the Reward Pathway Work?
The reward pathway is a series of brain structures that encode cues to help us repeat a rewarding experience. These cues include the person you are with, the clothes they are wearing, the food you eat, the odor of cologne or perfume, or a spoken phrase that makes you feel good.
When we receive these cues, our brains release chemicals, which alter the reward pathways in our brains. These changes can create feelings of pleasure or euphoria.
During adolescence, this reward system may become more sensitive to rewards, or it may be less responsive. It is unclear which mechanism is responsible for this change in reward-seeking behavior.
There are many other areas in the brain that interact with this reward pathway, including the hypothalamus, prefrontal cortex, and the locus coeruleus. These regions are critical in coordinating our interest in rewards with the body’s physiological needs.
What Happens to the Reward Pathway in Addiction?
The reward pathway is a part of the limbic system that controls feelings of pleasure. It works with other brain structures to determine whether a particular stimulus is rewarding or aversive.
In addiction, this pathway is hijacked by drug use. The drug’s actions commandeer the reward system to drive compulsive behavior toward drug seeking and use, and to extinguish adaptive behaviors that are less harmful to the body (for example, feeding or reproductive activity).
When someone first takes a substance, it may cause a rapid spike in the release of dopamine, which is a pleasurable sensation. Then, over time, the substance’s effects gradually become embedded in the brain, altering the reward pathway permanently.
