Most of us can recall a time when our mind blanked in an exam. Ironically, that vivid memory is of a time when we just couldn’t remember something. Part of the explanation for this contradiction is the stress hormone cortisol. While increased levels of cortisol boost the formation of memories, they can hinder their recall. Indeed, new research looking at more than 1,200 individuals finds that people whose cortisol levels stay higher during memory recall will find it more challenging to retrieve specific memories.
“Stress and cortisol strongly influence memory and are highly important modulators of learning and memory mechanisms,” says lead author Sandra Ackermann of the University of Basel in Switzerland. In the brain, cortisol binds to receptors that are found in the hippocampus and amygdala, which are important brain regions for learning and memory. Past work has found that inducing stress, thereby increasing cortisol, during or after learning benefits memory consolidation, while increasing cortisol during retrieval hinders recall. Furthermore, chronically elevated cortisol levels seem to impair memory.
In a collaborative effort, Ackermann and colleagues wanted to examine these effects on the individual level – testing how changes in people’s naturally occurring cortisol levels affected their performance on a memory task, rather than experimentally inducing stress or administering cortisol. They gave 1,225 healthy men and women a memory test and then measured their cortisol levels via saliva samples before memory encoding (when we form a memory), between encoding and recall, and after recall.
In the memory task, the researchers presented pictures that were either positive, negative, or neutral in the emotions they elicited. The subjects viewed the pictures and classified them as positive, negative, or neutral, and rated their emotional arousal. After 10 minutes and then 20 hours, the subjects had to freely recall the pictures.
As published online last month in the Journal of Cognitive Neuroscience, people with greater decreases in cortisol levels during memory retrieval had better recall performance of pictures, regardless of the emotional values of the pictures or whether it was 10 minutes or 20 hours later. Surprisingly, the researchers say, they did not find any association between cortisol levels and memory encoding.
“Given the results from previous studies where stress was experimentally induced, we anticipated that higher cortisol levels during encoding benefit memory while higher cortisol levels during memory recall hinder memory recall,” says Björn Rasch of the University of Zurich. What they found instead was that the level of cortisol itself was not as important as the change in cortisol during memory retrieval. “Our results suggest that persons with stronger basal responses to stress will have more difficulties to recall memories in stressful situations, for example, during exams,” Rasch says.
For those studying clinical disorders involving stress, such as post-traumatic stress disorder (PTSD) or depression, the study has significant implications. “Clinicians should focus more on the reactivity of the stress system as compared to single basal cortisol levels, which only represent an instantaneous picture,” Ackermann says. “The strength of the response to stressful stimuli might be more predictive for individual differences in stress vulnerability, such as for memory retrieval in our study, but maybe also for stress syndromes like PTSD or burnout.”
The next step for the work, which is currently performed at the University of Basel in the labs of Dominique de Quervain and Andreas Papassotiropoulos, is to investigate genetic underpinnings of associations between cortisol and memory. “In the brain, cortisol binds to specific receptors, and several genetic variations have been related to sensitivity of these receptors,” de Quervain says. “Therefore there may be differences in the strength of the association between cortisol and memory retrieval depending on the genotype”.
-Lisa M.P. Munoz
The paper “Associations between Basal Cortisol Levels and Memory Retrieval in Healthy Young Individuals,” Sandra Ackermann, Francina Hartmann, Andreas Papassotiropoulos, Dominique J.-F. de Quervain, and Björn Rasch, was published online in the Journal of Cognitive Neuroscience on June 28, 2013, and is forthcoming in print.
Media contact: Lisa M.P. Munoz, CNS Public Information Officer,