title: Bigger is better and worse: on the intricate relationship between hippocampal size and memory.
abstract: The structure-function relationship between the hippocampal region and memory is a debated topic in the literature. It has been suggested that larger hippocampi are associated with less effective memory performance in healthy young adults because of a partial synaptic pruning. Here, we tested this hypothesis in individuals with Fragile X Syndrome (FXS) with known abnormal pruning and IQ- and age-matched individuals with hypoxic brain injury, preterm birth, and obstetric complications. Results revealed larger normalized hippocampal volume in FXS compared with neurotypical controls, whereas individuals with hypoxic injury had smaller hippocampi. In neurotypical controls and individuals with hypoxic injury, better general memory, as indexed by the Wechsler Memory Scale-Revised, was associated with larger hippocampus. In contrast, in FXS we observed the opposite relationship: larger hippocampus was associated with worse general memory. Caudate volume did not correlate with memory in either group. These results suggest that incomplete pruning in young healthy adults may not contribute to less efficient memory capacity, and hippocampal size is positively associated with memory performance. However, abnormally large and poorly pruned hippocampus may indeed be less effective in FXS.
authors.affiliation: Nyírő Gyula Hospital, National Institute of Psychiatry and Addictions, Budapest, Hungary; University of Szeged, Faculty of Medicine, Department of Physiology, Szeged, Hungary; Budapest University of Technology and Economics, Department of Cognitive Science, Budapest, Hungary.
authors.forename: Katalin
authors.initials: K
authors.lastname: Molnár
authors.affiliation: Nyírő Gyula Hospital, National Institute of Psychiatry and Addictions, Budapest, Hungary; University of Szeged, Faculty of Medicine, Department of Physiology, Szeged, Hungary; Budapest University of Technology and Economics, Department of Cognitive Science, Budapest, Hungary. Electronic address: keri.szabolcs.gyula@med.u-szeged.hu.
authors.forename: Szabolcs
authors.initials: S
authors.lastname: Kéri
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D005260:Female; D005600:Fragile X Syndrome / Q000473:pathology; D006624:Hippocampus / Q000033:anatomy & histology* / Q000473:pathology; D006801:Humans; D000860:Hypoxia / Q000473:pathology; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D008609:Mental Status Schedule; D009483:Neuropsychological Tests; D055815:Young Adult
keywords: Fragile X Syndrome; Hippocampus; Intellectual disability; Memory