How Does Stress Affect the Brain?

Stress is known to affect the body and the mind. But stress, especially when chronic or prolonged, can also have a negative impact on the brain. Most people experience forgetfulness when stressed, but there are also changes happening to the brain that one doesn’t notice. So, what are these changes and how exactly does stress affect the brain?

Stress Changes the Brain’s Structure

Scientists at the University of California, Berkeley, have found that chronic stress leads to an increase in white matter in the brain, more specifically in the hippocampus (the part of the brain involved in emotion, learning, and memory). White matter is composed of networks of nerve fibers and makes up about half of the human brain. The white color comes from the substance that coats the nerve fibers, called myelin. An excess of myelin in the brain interferes with communication between the brain’s nerve fibers.

Stress Affects Short-Term Memory and Memory Retrieval

Chronic stress is associated with an increased risk of short-term memory loss. A study conducted by researchers at Ohio State University observed changes in the behavior of mice after repeated encounters with aggressive mice. Before the aggressive encounters, the mice were repeatedly placed in a maze with an escape hole, which they learned very well. After repeated stressful encounters with aggressive mice, the observed mice were unable to remember the location of the escape hole.

Moreover, acute stress (short-term stress) has been shown to affect how the brain collects and stores memories. Even stress lasting as little as a few hours can disrupt how brain cells communicate in the hippocampus region.

Stress Kills Brain Cells

A study published in 2005 showed that a single stressful social encounter is enough to lead to nerve cell death in the hippocampus from surviving. During this study, researchers placed a younger rat in a cage with two aggressive older rats for 20 minutes, then examined the brain of the younger rat under a microscope. Researchers found that the stress in the younger rats did not inhibit the hippocampus from generating new cells, but it did prevent a portion of the new cells from surviving — as little as one-third of newly generated cells survived one week later. Scientists also noted that the ability of the new nerve cells to survive was even affected one month after the stressful encounter, with as many as one-third having died.

Stress Shrinks Certain Areas of the Brain

Chronic stress is associated with the loss of brain volume and eventually cognitive impairment. A study conducted on rats showed that chronic stress resulted in a loss of volume in the hippocampus region of the brain. Studies on humans show that individuals diagnosed with post-traumatic stress disorder have a significant reduction of the hippocampus region of the brain. Loss of brain volume in the hippocampus affects its ability to make and store memories.

What Do These Findings Mean?

The relationship between stress and brain function could lead to new therapies that may help reduce the risk of developing long-term changes to the brain after experiencing stressful events.