Using Functional MRI brain scans, researchers found that those with lower levels of activity in the Prefrontal Cortex were more anxious, moody and depressed.
The Prefrontal Cortex is the area of the brain responsible for complex mental tasks, and activity here is critical if you want to be a high functioning human being.
The researcher Dr. Ahmad Hariri, a professor of psychology and neuroscience at Duke University, explained how the findings could greatly help those with anxiety and depression related conditions.
The article didn't talk about ways to increase activity in the Prefrontal Cortex but I know that meditation is one of the most powerful.
source: Cerebral Cortex, Nov 2017. https://doi.org/10.1093/cercor/bhx304