In this fascinating blog, Scott Alexander goes into many of the emerging theories surrounding depression. While many of us assume depression is caused by low serotonin levels and therefore can be improved by medications such as SSRIs, medications that decrease serotonin also can help improve depression. The overall picture that emerges is that depression is due to “decreased synaptogenesis.” This is another way of saying impaired neural plasticity, or disengagement from the environment. The aspect that is missing from this article is how Cognitive-Behavioral Therapy (CBT) can improve depressive symptoms. When behavioral psychologists examine why CBT works for depression, it becomes evident that Behavioral Activation is the main factor why depression lifts. In other words, re-engaging with the environment, despite the feelings of heaviness and fatigue, is eventually the path out of depression.