Relationship between hippocampal subfield volumes and memory function in adults born preterm with very low birth weight (VLBW)

Background: Being born preterm with very low birth weight (VLBW) is related to aberrant brain development. Hippocampus is a brain region particularly vulnerable to injury, for instance from consequences following preterm birth. The hippocampus is a complex structure with distinct subfields related to specific memory functions which are differently affected by neuropathological conditions. The relationship between deviations in hippocampal subfields and memory function has not been studied in adults born preterm with VLBW previously. Aims: In this long-term follow-up study of a geographically based cohort (birth years 1986-88) of VLBW individuals and term born controls with normal birth weight, the main aim was to examine group differences in memory function and hippocampal volumes at age 26 years. We also explored hippocampal structurefunction relationships in the VLBW group. Methods: Fifty-two VLBW and 82 control individuals aged 26 years were examined clinically of whom 44 VLBW and 70 controls had high-quality structural cerebral MRI at 3T. The participants were assessed with subtests from Wechsler Memory Scale and Cambridge Neuropsychological Test Automated Battery on verbal, visual and working memory. From the T1 weighted 3D images, hippocampal subfield volumes were estimated in FreeSurfer 6.0. In addition to group comparisons, partial correlations were performed in the VLBW group between hippocampal subfields’ volumes and neonatal risk factors, and between reduced hippocampal subfields’ volumes and performance on the memory tests. Results: Adults with VLBW had lower verbal, visual and working memory scores compared with term born control adults. Absolute hippocampal total and most subfield volumes were smaller in the VLBW group than in the control group, but with different findings in men and women. When adjusting for intracranial volume, left and right cornu ammonis fields and left dentate gyrus were smaller in VLBW women, while the right subiculum was smaller in VLBW men compared with control women and men, respectively. There was a negative correlation between days on mechanical ventilation and volume of the left subiculum in the VLBW group. Smaller left dentate gyrus volume was associated with lower visual memory performance in the VLBW group. Conclusions: Adults born preterm with VLBW had lower performance on memory tests and smaller hippocampi compared with term born controls, and volume of dentate gyrus was associated with visual memory. Hippocampal subfield volumes seem to be differently affected following preterm birth in VLBW men and women. *Correspondence to: Synne Aanes, Department of Clinical & Molecular Medicine, Faculty of Medicine & Health Sciences, Norwegian University of Science & Technology, 7489 Trondheim, Norway, E-mail: Synne.aanes@gmail.com