How Depression Affects The Brain – Yale Medicine Explains

Research shows that the hippocampus is smaller in some depressed people. For example, in one fMRI study published in The Journal of Neuroscience, investigators studied 24 women who had a history of depression. On average, the hippocampus was 9% to 13% smaller in depressed women compared with those who were not depressed. The more bouts of depression a woman had, the smaller the hippocampus. Stress, which plays a role in depression, may be a key factor here, since experts believe stress can suppress the production of new neurons (nerve cells) in the hippocampus.
Researchers are exploring possible links between sluggish production of new neurons in the hippocampus and low moods. An interesting fact about antidepressants supports this theory. These medications immediately boost the concentration of chemical messengers in the brain (neurotransmitters). Yet people typically don’t begin to feel better for several weeks or longer. Experts have long wondered why, if depression were primarily the result of low levels of neurotransmitters, people don’t feel better as soon as levels of neurotransmitters increase.Amygdala: The amygdala is part of a group of structures deep in the brain that’s associated with emotions such as anger, pleasure, sorrow, fear, and sexual arousal. Recalling an emotionally charged memory, such as a frightening situation, activates the amygdala. Activity in the amygdala is higher when a person is sad or clinically depressed, and this continues even after recovery from depression. This increase in activity may actually cause the amygdala to enlarge.
Basal ganglia (not pictured): The basal ganglia are a related group of structures deep in the brain. They are connected to and interact with structures that are closer to the brain’s surface. They may help facilitate movement and may be involved in memorizing, thinking, and emotional processing. Some studies have found shrinkage and other structural changes in the basal ganglia in people with depression.
Hippocampus: The hippocampus plays a key role in processing long-term memory. Interplay between the hippocampus and the amygdala might account for the adage “once bitten, twice shy.” It is this part of the brain that registers fear when you are confronted by a barking, aggressive dog, and the memory of such an experience may make you wary of dogs you come across later in life. The hippocampus is smaller in some depressed people, and research suggests that ongoing exposure to stress hormones impairs the growth of neurons in this part of the brain.