One of the main areas of neurogenesis in the human brain is the hippocampus, the temporary way station in your brain for information before a small portion (less than 1% of all of the information you receive) is retained as memory traces in other parts of the brain.
What determines what is retained? One factor appears to be the emotional salience of the information. There are several ways that this shows up. For example, early stages of dementia are marked by difficulty recalling recent experiences, but the difficulty is not uniform; some information is more easily recalled. Many older people who are struggling with everyday memory also have clear recollections of recent events that have made them angry or frustrated. The reason is that emotional salience causes information to be retained, even if the emotion is negative. Conversely, people who are happy and optimistic more often give their experiences positive emotional salience, resulting in disproportionate retention of information that tends to be recalled positively. For these people, the glass is not only half-full, the milk is cold and satisfying.
Now, stick with me on this next part, which may be important for your personal future. When positive information is self-referent (referring to your self-image), you feel better about yourself and you tend to evaluate experiences more positively, which leads you to be more resilient, even in the face of dire emotional and physical challenges. This resilience translates into handling stress better, which results in lower cortisol levels. This is important because high levels of cortisol damage and limit the growth of dendrites, the tiny spines that emerge from the cell body to link with other neurons. If cortisol damage is severe and long-standing, the neuron will die. Thus, positive emotional salience of information leads to emotional resilience, which leads to neuronal protection and hippocampal health.
I pay attention to my emotional inputs and try to avoid or minimize negative inputs. I find that my clients who have disorders involving depression and anxiety benefit greatly from guidance to do the same. Click on the hippocampus tag at the end of this post for the Happy Hippocampus activities I give my clients to stimulate positive emotional and cognitive development.