If you think about it, most of our daily lives revolve around food: when our next meal will be, what it will be, and how yummy it will be! Evolutionarily, these have been essential thoughts for our survival, so that when we find food, we are compelled to eat as much as we can. Not only does this ensure that we get all our necessary nutrients, but it also keeps competitors from stealing our meals.
How is it that we can swallow “one more bite” of our favorite dessert, even after we are so full? The study by DiFeliceantonio et al. (2012) that JL wrote about earlier this week showed that a new area of the brain, called the neostriatum, is involved the brain’s reward system. The brain activates an opiate system there to counteract the discomfort of our swelling belly so that we may continue to eat. In addition to this system, the brain’s dopamine reward pathway is central in making us feel good when we do things that are beneficial for our survival, like eating, drinking, and reproduction.
But what other areas of the brain are involved in this pathway? The reward pathway begins in the center of the brain in a region called the ventral tegmental area. Here, special neurons release the neurotransmitter dopamine, which gives you a jolt of pleasure and makes you feel good. In order to make sure you repeat this behavior in the future, the reward pathway is connected to areas of the brain that control memory and behavior. If you remember that eating a cheeseburger, for example, made you feel good, then you will be more likely to eat it again. If your brain strengthens the connections that allow this rewarding behavior to occur (such as picking up the cheeseburger, chewing it, and swallowing it), then it will be easier for you to do next time. If we do eat another cheeseburger, we will again feel a jolt of pleasure. Through this reward pathway, our brain has ensured that we will repeat this behavior in the future!
However, repeating a pleasurable behavior is not always a beneficial behavior. For example, addictive drugs activate the reward pathway, causing the cells to increase the amount of dopamine in the area, creating an intense “high.” The brain compensates for these sudden changes by reducing the number of cells that can respond to dopamine, so that the next time a drug is used, the effect is not as strong. Unfortunately, this also causes the user to increase their drug use in order to get that same “high,” a term called “tolerance.” As the brain continues to adapt to these drugs, the regions of the brain responsible for judgment and memory are also changed. This “hard-wiring” makes drug-seeking behavior a habit, and the user becomes a drug addict.
Understanding the reward pathway and its relation to other areas of the brain, like the neostriatum, is essential so that we may be able to stop the cycle or reduce its effects and help those afflicted with addictions.Image adapted from BrainFacts.org