Association between cytokine levels, verbal memory and hippocampus volume in psychotic disorders and healthy controls

Objective: We investigated whether elevated plasma levels of immune markers were associated with verbal memory and hippocampal subfield volumes in patients with severe mental illnesses and in healthy controls. Method: In total, 230 patients with a broad DSM-IV schizophrenia spectrum illness or bipolar disorder and 236 healthy controls were recruited. Memory was assessed using the Wechsler Memory Scale Third Edition (WMS-III) Logical Memory immediate and delayed recall, and the California Verbal Learning Test summed recall over learning list (CVLT learning) and delayed free recall. We measured plasma levels of soluble tumor necrosis factor receptor 1 (sTNF-R1), interleukin-1 receptor antagonist, interleukin-6, von Willebrand factor, osteoprotegerin, high-sensitivity C-reactive protein and sCD40 ligand. Hippocampal subfield estimates were obtained using FreeSurfer. Results: We found a moderate negative association between sTNF-R1 and performance on verbal memory learning and recall tests as measured by the WMS-III Logical Memory after controlling for age, sex and diagnosis. We observed no interaction effect of diagnosis and sTNF-R1 on memory scores. We also found a nominally significant positive association between CVLT learning and hippocampal volumes. Conclusion: The findings suggest a role for immune involvement in memory independent of severe mental disorders and may support the `bigger is better' hypothesis of hippocampal subfield volumes.