Memory and the hippocampal formation following pediatric traumatic brain injury.

Introduction: Previous research indicates disruption of learning and memory in children who have experienced traumatic brain injury (TBI). Objective: This research evaluates the impact of pediatric TBI on volumetric differences along the long axis of the hippocampus, a region of the brain that is critical for explicit memory. Methods: Structural brain data and behavioral measures were collected 6 weeks following TBI or extracranial injury (EI), in children aged 8-15 years and from a group of age matched typically developing controls (TDC). Total hippocampal volume and hippocampal subregion volumes corresponding to hippocampal head, body, and tail were compared across groups and were examined in relation to verbal and visual memory. Results: Group differences were evident such that hippocampal body volume was found to be smaller for TBI and EI groups compared to the TDC group. Analysis restricted to the TBI group indicated that hippocampal head volume was associated with severity of injury. The relation between severity of injury and hippocampal head volume is particularly important considering results from our investigation of hippocampal volume-to-memory performance relations indicating positive correlations between hippocampal head volume and performance on memory measures for both the TBI group and the TDC group. Significant negative correlations between hippocampal body volume and memory were evident for the TBI group but not EI or TDC groups. Correlations between memory performance and hippocampal tail volume were not significant for the TBI or TDC groups, although for the EI group, a positive correlation was found between hippocampal tail volume and memory. Conclusion: Together these results underscore an important relation between hippocampal structure and memory function during the subacute stage of recovery from pediatric TBI.