A reliable and valid method for manual demarcation of hippocampal head, body, and tail

There is a growing interest in characterizing functional specialization along the long axis of the hippocampus in humans. Variability in volumetry along the long axis of the hippocampus may be of functional relevance in human development, and in a number of clinical populations. However, there is a lack of consistent definitions for measurements of regional volumetry along the hippocampal long axis. Moreover, there is lack of consistent reliability standards of these measures. Here we describe a protocol for manual demarcation of hippocampal head, body, and tail. The definitions emphasize anatomical landmarks that agree with the extant literature and are visible in children and adults alike. Using this protocol we achieved high reliability of all volumetric measures. We further demonstrate that the protocol can be applied to T2-weighted images optimized for high-resolution scanning of the hippocampus, as well as a more standard T1-weighted image sequence. Third, the protocol is sensitive to detect individual differences in subregion volumes in normally developing children (N=81; ages 8-25 years). This protocol may be of use for researchers studying the hippocampus across the lifespan and in diverse clinical populations.