You have probably experienced that feeling of not being as mentally sharp as normal when you are under a lot of stress. Recent research has demonstrated that the human brain functions less well under stress, and we now know that stress causes actual physical changes in the brain, and those changes are directly associated with a decrease in brain function.
The original research in this area was first performed with rats as subjects. Later tests with human subjects generated similar results. Let’s take a quick look at each case:
Case #1: The Rats.Bruce McEwen and John Morrison at Mount Sinai Medical Center found that in the rat’s brain under stress, nerve cells of the prefrontal cortex shrink, resulting in slower performance on attention-shifting tasks. On the other hand, neurons in the orbital frontal cortex used response-reversal tasks actually grew larger. A response-reversal task is one where a subject is reinforced for giving response A to stimulus A and response B to stimulus B. Then, they are placed in a reversed situation where they must give response B to stimulus A and response A to stimulus B. The test measures how well they can “reverse” their responses. In the face of such tasks, the plastic brains of the rats adapted to the stress stimuli and physically changed to address the conditions.
Case #2: The Humans.Conor Liston and B. J. Casey of the Sackler Institute used brain imaging to study male medical students preparing for their board exams and compared them to healthy students who were not experiencing the stress of studying for exams. The students were asked to perform two different mental tasks while their brains were being scanned with MRI. The stressed students were less able to shift their attention from one task to another and showed changes in the prefrontal cortex. Interestingly, their ability to perform response-reversal tasks was not impaired by stress; subjects were still able to “change their minds” when presented with information that changed their responses to a certain situation.
In both cases, we see experiments producing similar results when it comes to attention-shifting tasks and response-reversal tasks. Not only that, tests showed that the physiological effects were temporary in the rats as well as the humans. When Liston and Casey repeated the brain scans in their med students one month after the board exams were over -- and the stress was gone from the equation -- they found that the attention shifting ability and the brain scans of the stressed students had returned to normal.
So we are able to conclude that while stress causes changes to the brain and decreases some brain functions, the brain is able to recover fairly quickly. Once again, the research demonstrates how the plastic neural network of the brain – whether rat or human -- is constantly changing to address the stimuli it experiences and function at optimal capacity for its given external environment.
Further research on the effects of stress on the brain may help us to better understand how people respond to stress and could help in the understanding and treatment of stress-associated psychiatric disorders.
Stress disrupts human thinking, but the brain can bounce back. January 27, 2009.