Natural Reward Pathways
The brain is divided into several sections, and the reward pathway is in the center of these. The reward pathway controls feelings of motivation, reward, and behavior, but its' main job is to make us feel good when we do things that are necessary for survival, like eating, drinking, and sex. The pathway connects to other important sections in the brain to gather info about what's happening outside of the body, and to strengthen brain circuits and control desirable behaviors. For example, when you are hungry and you see a sandwich, your five senses gather information about your surroundings and send signals to the brain to let you know that there is a sandwich in front of you. Based on the knowledge that if you eat, you won't be hungry anymore, the brain tells you to eat the sandwich. When you eat the sandwich, special neurons in the reward pathway release dopamine, which gives you a little jolt of pleasure, which is your reward for eating the sandwich. As well as rewarding you for performing beneficial tasks, the reward pathway makes sure you repeat this action whenever you can. It does this by connecting to the parts of the brain that control memory and behavior. When the pathway signals these regions, the brain creates the memory that eating food makes you feel good, increasing the chance of you eating food again. When the reward pathway signals the brain's motor center, it strengthens the wirings for behaviors that help you achieve your reward. In the sandwich example, those behaviors would be picking it up, chewing it, and swallowing it. Overall, the reward pathway's purpose is to make sure that we repeat behaviors necessary for survival.
Drugs Alter the Brain's Reward Pathway
Within seconds of entering the body, drugs can cause dramatic changes to the brain's synapses. By passing the five senses and going straight to the brain, drugs can cause intense jolts of pleasure. Drugs affect the brain to so much that the brain must try to adapt. One way it does this is by reducing the number of dopamine receptors at the synapse. As a result, next time the user want to get high, they will need more of the drug. This is referred to as "tolerance." As the brain adapts to the presence of drugs, regions outside of the reward pathway are affected, such as regions responsible for judgement, learning and memory. These regions begin to physically change and become "hard-wired." Once this happens, drug seeking becomes more of a habit or reflex. This is how a drug user becomes a drug addict. Drugs can even cause changes to the brain that are so dramatic, they can be fatal.
