Adamson MM, Bayley PJ, Scanlon BK, Farrell ME, Hernandez B, Weiner MW, Yesavage JA, TaylorJL. Pilot expertise and hippocampal size: associations with longitudinal flight simulator performance. Aviat Space Environ Med 2012; 83:850–7. Background: Previous research suggests that the size of the hippocampus can vary in response to intensive training (e.g., during the acquisition of expert knowledge). However, the role of the hippocampus in maintenance of skilled performance is not well understood. The Stanford/Veterans Affairs Aviation MRI Study offers a unique opportunity to observe the interaction of brain structure and multiple levels of expertise on longitudinal flight simulator performance. Methods: The current study examined the relationship between hippocampal volume and three levels of aviation expertise, defined by pilot proficiency ratings issued by the U.S. Federal Aviation Administration (11). At 3 annual time points, 60 pilots who varied in their level of aviation expertise (ages ranging from 45 to 69 yr) were tested. Results: At baseline, higher expertise was associated with better flight simulator performance, but not with hippocampal volume. Longitudinally, there was an Expertise × Hippocampal volume interaction, in the direction that a larger hippocampus was associated with better performance at higher levels of expertise. Discussion: These results are consistent with the notion that expertise in a cognitively demanding domain involves the interplay of acquired knowledge (‘mental schemas’) and basic hippocampal-dependent processes.