Is an increase in cortisol levels associated with impaired working-memory retrieval and recognition in students?

By Dr. Chinta SidharthanReviewed by Danielle Ellis, B.Sc.May 4 2023

In a recent study published in the journal Behavioral Sciences, researchers examined the memory scores and electroencephalogram (EEG) profiles of students to understand exam-induced stress and anxiety among the student population.

Background

Stressful events cause alterations in the central nervous system, triggering cortisol secretion and the fight-or-flight response. The increase in cortisol levels increases the energy levels and suppresses the immune system. Furthermore, while the number of stress response hormones secreted depends on the severity of the stress, cortisol levels, and stress are consistently correlated. There is also a temporal association between stress response and memory formation with respect to learning.

An EEG is an ideal tool to study the brain's electrical activity since it is non-invasive, and the method is now widely used in diagnosing depression, epilepsy, and various neurological conditions. Studies have also found that stress causes changes in EEG activity. The EEGs of medical students have shown increased beta activity levels in the weeks leading up to examinations. Decreases in the alpha and theta activity have also been observed in the EEG in association with examination-related stress among students.

About the study

In the present study, the researchers investigated whether increased cortisol levels associated with examination stress among students were linked to impaired retrieval of working memory and recognition. The cortisol levels and EEG profiles of students were measured at the onset of the semester and again during the examination period. The study focused on the medial frontal gyrus, the middle frontal gyrus, and the parahippocampal gyrus.

The participants were students of Laurentian University, Canada, registered in undergraduate programs. The mean age of the study population was 21 years. The memory test comprised viewing various nondescript, black-and-white images for 30 seconds and a recollection of those images at the end of the experiment. Additionally, saliva samples were collected from all participants during the afternoon, and an enzyme-linked immunosorbent assay (ELISA) was used to determine cortisol levels. Electroencephalography was performed for each participant at the beginning of the semester and once again during the examination period.

Results

The results reported correlations between cortisol levels, parahippocampal activity, and memory performance. Changes in the mean current source density were also observed in the medial frontal gyrus during the experiment. The middle frontal gyrus activation increased during the examination periods when the individual’s memory scores were consistent between the two readings. The activation of the parahippocampal gyrus was the highest one day before the examination.

The middle frontal gyrus is associated with working memory, and the study found that working memory impairments affect information storage and retrieval processes. For the individuals who showed a greater difference in memory performance between the initial and later measurements, the middle frontal gyrus activity was reduced. This indicated that during a stressful event, the middle frontal gyrus increases its activity to perform as well as during periods of relaxation.

Memory performance was also positively correlated with parahippocampal gyrus activity, while cortisol levels were negatively associated with memory performance and parahippocampal gyrus activity. Although the hippocampus is involved in the consolidation of memory, the neocortex, which is part of the parahippocampal gyrus, is involved in the permanent development, storage, and retrieval of memory. Cortisol release disrupts the structure of the parahippocampal gyrus and affects its ability to retrieve information.

The current source density of the parahippocampal gyrus was also higher in individuals who were yet to write their exams than those who had completed their exams. This region of the brain is in the limbic system, which is involved in behavior and is activated by a stressful event. The findings showed that the parahippocampal gyrus activity was significantly lower in individuals who were relaxed after completing their exams as compared to those who were stressed and awaiting their exams.

Conclusions

Overall, the findings indicated that the measurement of cortisol levels and EEG profiles could be used to study the alterations in brain activity related to stress. Cortisol levels were negatively correlated with the activity of the parahippocampal gyrus and memory performance. Furthermore, the middle frontal gyrus showed increased activity levels when trying to maintain memory performance under periods of stress.