The relationship between stress and memory is complex. A little bit of stress can enhance your ability to encode, store, and retrieve factual information. Too much stress, however, can shut the system down. You may have had this experience studying for a test. A moderate amount of anxiety is motivating and will help you perform better. Too much on the other hand, especially while taking the actual test, can prevent you from recalling what you know.
The experience of trauma and chronic stress over time can actually change the brain structures involved in memory. To understand how this happens, we need to consider one of the ways memories are formed and recalled.
When we have a sensory experience, the amygdala (associated with processing emotion) influences the hippocampus (associated with processing memory) to encode and store the information. Emotionally charged events (both positive and negative) form stronger memories. Later, when it comes time to retrieve a memory, the prefrontal cortex gives the command.
All three of these brain structures are also involved in traumatic stress.
Chronic Stress and Memory
When we experience a threat, the amygdala sets off an alarm which puts the nervous system and body into fight or flight mode. This system exposes the brain and body to high levels of circulating stress hormones. Research has shown that high levels of stress hormones over time can damage the hippocampus (it actually shrinks). This reduces its ability to encode and form memories.
Additionally, during times of stress, the amygdala will inhibit the activity of the prefrontal cortex. From a biological perspective, this is useful in keeping us alive. Energy and resources are pulled away from higher thought and reasoning (the prefrontal cortex) and re-directed to bodily systems needed to preserve our physical safety. For example, our sensory abilities are heightened. Our muscles receive oxygen and glucose so we can fight or run.
For most if us, the fight or flight response is usually not needed to keep us alive in today’s society. It is not useful during an interview for a job you really want or while out on a date. A chronically activated nervous system actually reduces our ability to function and, over time, damages certain structures in our brain.
Trauma and the Hippocampus
To investigate the effects of trauma on the hippocampus researchers looked at the brains of coal miners who had developed posttraumatic stress disorder (PTSD) after being involved in an explosion (2). The researchers found that the coal miners with PTSD had significantly reduced volume of the amygdala and hippocampus in comparison to non-traumatized coal miners.
These findings hold important implications when it comes to memory. Reduced volume in the hippocampus and amygdala due to chronic stress reduces the ability to form and recall memories.
What We Can Do
The brain retains its ability to change throughout the entire lifespan. Studies have already shown that the damaging effects of chronic stress and trauma on the hippocampus can be reversed. For example, the use of antidepressant medication that increases serotonin levels has been shown to counteract the effects of stress on the hippocampus. With antidepressant use, the hippocampal volume in the chronically stressed brain increased.
While the mechanism for the changes in the hippocampus is not fully understood, we can assume that in addition to the increase in serotonin, the reduction in stress that caused the damage in the first place, also plays a role in the reversal of damage to the hippocampus.
Take the steps necessary to reduce chronic stress. Not only will lower stress have a positive effect on your overall quality of life, but it may also begin the process of healing the damage to the brain structures involved in memory. Exercise, therapy, and medication are all options for reversing damages of trauma and chronic stress.
- Bremner, J. D. (2006). Traumatic stress: effects on the brain. Dialogues in clinical neuroscience, 8(4), 445.
- Zhang, Q., Zhuo, C., Lang, X., Li, H., Qin, W., & Yu, C. (2014). Structural impairments of hippocampus in coal mine gas explosion-related posttraumatic stress disorder. PloS one, 9(7), e102042.
- Malberg, J. E., Eisch, A. J., Nestler, E. J., & Duman, R. S. (2000). Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus. Journal of Neuroscience, 20(24), 9104-9110.
- Power, J. D., & Schlaggar, B. L. (2017). Neural plasticity across the lifespan. Wiley Interdisciplinary Reviews: Developmental Biology, 6(1), e216.