Chronic social stress and hippocampal memory system in older adults
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Perceived social discrimination, a salient chronic psychosocial stressor, has an adverse effect on physical and mental health. Cumulative stress compromises adaptive physiologic processes and triggers changes in hypothalamic-pituitary-adrenocortical (HPA) axis functioning. The hippocampus is critical for episodic memory and mediates the HPA stress response. Animal models have demonstrated increased vulnerability of the hippocampus to stress-induced morphological alterations and dysfunction. Previous research has shown that greater psychosocial stress is related to poorer episodic memory performance in older adults. Diffusion-weighted imaging (DWI) studies strongly support the role of the uncinate fasciculus (UF) in episodic memory. Furthermore, psychosocial stress has been associated with white matter (WM) microstructural abnormalities in the UF. Although the effect of chronic psychosocial stress is well established, the effects of social discrimination on WM integrity and episodic memory are not well understood. In this study, we tested the hypothesis that greater perceived social discrimination in older adults is associated with poorer episodic memory performance and structural abnormalities of the UF tract. Twenty-eight participants (63.8 – 73 years, 57.1% female, 42.9% African American) reported experiences of discrimination (EoD) and perceived stress (PSS) and were assessed for episodic memory. High angular resolution diffusion imaging (HARDI) scans were analyzed with probabilistic tractography to examine associations of UF diffusion metrics with EoD scores and episodic memory performance. Spearman’s rank correlation determined a significant positive association between EoD and PSS scores (rs(28) = 0.45, p = 0.017), suggesting perceived discrimination is a chronic stressor and may be a social determinant of health. However, contrary to our expectations, neither EoD nor PSS were significantly related to episodic memory performance and UF diffusion metrics. Future longitudinal research to examine associations between perceived discrimination, episodic memory and WM microstructure in a large cohort is warranted.