Real-space navigation in patients with focal epilepsy underpins the prominent role of the hippocampus for allocentric navigation in humans.

BACKGROUND

An in-depth assessment of spatial navigation in patient cohorts with focal brain disorders may inform about the functional topography of underlying brain networks. The aim of the current study was to investigate the role of the right and left hippocampi on recombining novel routes in a real-space environment as a correlate for allocentric navigation abilities in patients with focal epilepsies.

METHODS

In a single-center approach, adults with unifocal epilepsy were prospectively recruited from the tertiary epilepsy center at LMU Munich. 16 patients with right-sided mesial temporal lobe epilepsy (rTLE), 16 with left-sided mesial temporal lobe epilepsy (lTLE), 15 with frontal lobe epilepsy (FLE), and 24 age-matched healthy controls conducted a real-space navigation paradigm that required recognition of familiar routes and recombination of novel routes. Visual exploration behavior and navigation trajectories were documented by a gaze-controlled head-fixed camera and analyzed post hoc across groups and navigation conditions.

RESULTS

Epilepsy patients (mean age 40.7 years) performed significantly worse in finding navigation targets than controls (p<0.001). Age, duration of epilepsy, and structural brain lesions affected navigation performance. After correcting for confounders, rTLE patients showed significantly inferior performance compared to FLE, especially for recombined novel routes. lTLE patients were impaired mainly on recombined novel routes. rTLE patients spent more time at crossroads and used shortcuts less often than controls.

CONCLUSION

This study supports the hippocampus as a major hub for human goal-oriented navigation in real environments, with right hippocampal dysfunction particularly impairing allocentric navigation and creation of novel routes.