The human raphe-hippocampal tract and affective sensitivity: a probabilistic tractography study.

Serotonergic system plays critical roles in modulating affective control. The raphe nucleus has been known to be the origin of forebrain 5-HT afferents. Specifically, the Raphe-Hippocampal projection has been shown to modulate affective sensitivity in rodents. However, the human Raphe-Hippocampal tract is not well studied. We aimed to segment the Raphe-Hippocampal tract using probabilistic tractography on diffusion tensor imaging data from 502 subjects. The Raphe-Hippocampal tracts were successfully isolated in 464 individuals. There was a significant association between integrity of the Raphe-Hippocampal tract and affective sensitivity. To our best knowledge, this is the first study that isolated the human Raphe-Hippocampal tract. The integrity of the tract showed consistent characteristics with rodent findings, where affective sensitivity is modulated by the Raphe-Hippocampal projection. This study provides a technique to segment the human Raphe-Hippocampal tract and a translational knowledge that the tract in a human possesses consistent characteristics that have been found in rodent studies.