The associations among hippocampal volume, cortisol reactivity, and memory performance in healthy young men

In aged and pathological populations, reduced hippocampal volume is frequently described in association with impairment of hippocampus-dependent cognitive processes and chronically elevated cortisol levels. Recent studies in young healthy subjects show a negative association between hippocampal volume and memory. The aim of the present study was to investigate the associations among hippocampal volume, cortisol levels and memory performance in a group of healthy young men. Hippocampal volume was determined by manual segmentation of high-resolution 3D Magnetic Resonance Images from 13 subjects. Stress-induced cortisol levels in response to the "Trier Social Stress Test" (TSST) as well as the cortisol response to awakening (CRA) over four weeks were assessed. Declarative memory performance was tested before and after exposure to the TSST. The results show that larger hippocampal volume was associated with a significantly stronger cortisol increase in response to the TSST and a significantly greater CRA. Moreover, larger hippocampal volume was associated with significantly lower memory performance before the TSST. Our results challenge the direction of the frequently observed relationships among hippocampal volume, cortisol reactivity and memory performance and question the relevance of findings in clinical and aged subjects for young healthy populations.