The Biological Effects of Stress on Memory During Healthy Ageing

Abstract

Psychosocial stress is an everyday experience that can potentially impact cognition. High levels of stress across the lifespan are thought to negatively impact brain structures that mediate both stress response and memory. Therefore, we aimed to explore the influence of acute psychosocial stress, and stress across the lifespan, on the brain and cognitive abilities. First, a meta-analysis assessed the literature on the effects of psychosocial stress on memory and cognition. We identified a minimal impact of psychosocial stress on episodic memory. This differed from previous meta-analyses that found an enhancing effect of post-encoding stress and impairing effects of stress on memory immediately before retrieval. We then conducted a series of four behavioural experiments to identify the features of memory influenced by psychosocial stress. These showed a minimal impact of psychosocial stress on episodic memory. However, increased stress responsivity may be associated with enhanced recollection in the stress group. Our behavioural studies also identified substantial inter-individual differences in how people responded to acute stress. We therefore aimed to examine the neural mechanisms potentially underpinning high and low reactivity to psychosocial stress. Using MRI, we aimed to compare brain structure, function, and neurochemical differences between individuals with high and low levels of trait stress reactivity. This study was postponed due to COVID-19. A second set of studies were conducted to examine the impact of repeated exposure to high stress levels on cognition and brain structure in later life. Using UK Biobank data, we defined groups with previous exposure to highly stressful events. We first demonstrated that high levels of stress across the lifespan were negatively associated with cognition and mental health. When looking at brain structure, we found that females demonstrated a link between high stress levels and altered microstructure in the posterior thalamic radiation. We then analysed grey matter regions in a subsample of participants, and demonstrated that in males only, high levels of lifetime stress were associated with reduced microstructural integrity in the hippocampus. Together these studies highlight the impact of acute psychosocial stress and a history of repeated exposure to stressful experiences on cognition and their brain mechanisms . Crucially, it should also be noted that the effects of acute psychosocial stress appear to be distinct from other forms of stress previously reported in the literature.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Hamied Haroon (Supervisor), Geoff JM Parker (Supervisor), Deborah Talmi (Supervisor) & Nils Muhlert (Supervisor)