title: There and Back Again: Hippocampus and Retrosplenial Cortex Track Homing Distance during Human Path Integration.
abstract: Path integration, the updating of position and orientation during movement, often involves tracking a home location. Here, we examine processes that could contribute to successful location tracking in humans. In particular, we investigate a homing vector model of path integration, whereby a navigator continuously tracks a trajectory back to the home location. To examine this model, we developed a loop task for fMRI, in which participants viewed movement that circled back to a home location in a sparse virtual environment. In support of a homing vector system, hippocampus, retrosplenial cortex, and parahippocampal cortex were responsive to Euclidean distance from home. These results provide the first evidence of a constantly maintained homing signal in the human brain. In addition, hippocampus, retrosplenial cortex, and parahippocampal cortex, as well as medial prefrontal cortex, were recruited during successful path integration. These findings suggest that dynamic processes recruit hippocampus, retrosplenial cortex, and parahippocampal cortex in support of path integration, including a homing vector system that tracks movement relative to home.
  
  
  CONCLUSIONS
  Path integration is the continual updating of position and orientation during navigation. Animal studies have identified place cells and grid cells as important for path integration, but underlying models of path integration in humans have rarely been studied. The results of our novel loop closure task are the first to suggest that a homing vector tracks Euclidean distance from the home location, supported by the hippocampus, retrosplenial cortex, and parahippocampal cortex. These findings suggest a potential homing vector mechanism supporting path integration, which recruits hippocampus and retrosplenial cortex to track movement relative to home. These results provide new avenues for computational and animal models by directing attention to homing vector models of path integration, which differ from current movement-tracking models.
authors.affiliation: Department of Psychological and Brain Sciences and Center for Memory and Brain, Boston University, Boston, Massachusetts 02215, and Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129 chrastil@bu.edu.
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Chrastil
authors.affiliation: Department of Psychological and Brain Sciences and Center for Memory and Brain, Boston University, Boston, Massachusetts 02215, and Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129.
authors.forename: Katherine R
authors.initials: KR
authors.lastname: Sherrill
authors.affiliation: Department of Psychological and Brain Sciences and Center for Memory and Brain, Boston University, Boston, Massachusetts 02215, and.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hasselmo
authors.affiliation: Department of Psychological and Brain Sciences and Center for Memory and Brain, Boston University, Boston, Massachusetts 02215, and Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129.
authors.forename: Chantal E
authors.initials: CE
authors.lastname: Stern
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D002540:Cerebral Cortex / Q000098:blood supply / Q000502:physiology*; D006624:Hippocampus / Q000098:blood supply / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D009434:Neural Pathways / Q000098:blood supply; D009949:Orientation / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D013037:Spatial Behavior / Q000502:physiology*; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: angular gyrus; fMRI; medial prefrontal cortex; navigation; parahippocampal cortex; precuneus