Stress Affects Intentional Control of Memory
New research should aid psychological counseling.
Posted October 1, 2020
It is well known that intentional use of mnemonics can improve the formation and recall of memory. Intentional memory control is assumed to help us to remember valued memories while suppressing memories that pose a threat to our integrity or well-being. However, memory experts often conclude that we have little control over certain intentional aspects of memory, especially in cases of anxiety, depression, and PTSD. Various studies have shown that the ability to suppress unwanted memories comes from strong electrical coupling that is manifest in the theta frequency band syncing between the hippocampus and frontal cortex.
A study of this matter has recently been reported. I have posted several blog posts before showing that chronic stress and the associated glucocorticoid hormone (cortisol) release impair memory by interfering with synapse formation. However, here what was tested was the immediate effect of a single acute stress experience.
The study design used two groups of humans, one exposed to acute stress and the other a non-stressed control group, before they aimed to retrieve certain previously learned cue-target face-word pairs and to actively suppress others. The stress was a standard stressful personal interview test. Subjective stress rating, blood pressure, and salivary cortisol levels confirmed the successful stress induction.
Shortly after the stress, participants engaged in a think/no-think procedure in which they repeatedly tried to actively retrieve or suppress the previously learned associations while magnetoencephalography (MEG) was recorded. The MEG was analyzed for cross-spectral coherence of theta activity in the hippocampus and frontal cortex.
Control participants showed reduced memory during suppressed trials compared with baseline pairs in a subsequent memory test. This suppression-induced forgetting was completely abolished after stress, even though stress did not impair recall of face-word pairs that were not tagged to be suppressed. (The face-word pairs designated to be suppressed were not emotionally disturbing. The assumption is that emotionally disturbing memories would have been even harder to suppress in this test design.)
It is not clear if the impairment of memory control directly came from cortisol. The suppression-induced forgetting was associated with stress-induced cortisol increases and decreased electrical connectivity between the hippocampus and right dorsolateral prefrontal cortex (PFC). The association of cortisol and weakened memory suppression could have been coincidental and due strictly to reduced electrical coupling. It is also not clear whether cortisol has direct action on the kind of electrical coupling reported here.
The obvious practical point of this research is that acute stress made it more likely that previously acquired memory could not be suppressed. Thus, people with unwanted memories, as in PTSD, have difficulty in selectively suppressing bad memories if they experience new stress. This phenomenon creates a vicious circle of emotional distress. When life experience creates bad memories, the ability to suppress them and their bad psychological effects is impaired when new stress is experienced. Thus, psychological therapy would be optimized by assuring that there are no new stressful experiences during the counseling.
C.W.E.M. Quaedflieg, T.R. Schneider, J. Daume, A.K. Engel and L. Schwaber (2020). Stress Impairs Intentional Memory Control through Altered Theta Oscillations in Lateral Parietal Cortex. Journal of Neuroscience 40 (40), 7739-7748; DOI: https://doi.org/10.1523/JNEUROSCI.2906-19.2020