Frontal-midline oscillations index the evolution of spatial memory during active navigation.

Previous research has demonstrated that humans combine multiple sources of spatial information, such as allothetic and idiothetic cues, while navigating through an environment. However, it is unclear whether this involves comparing multiple representations from multiple sources during encoding (parallel hypothesis) or primarily accumulating idiothetic information until the end of the navigation to integrate with allothetic information (serial hypothesis). We tested these two hypotheses in an active navigation task using mobile scalp EEG recordings. Participants walked through an immersive virtual hallway with or without conflicts between allothetic and idiothetic cues and pointed toward the starting position of the hallway. By analyzing the scalp oscillatory activities during the navigation phase, we found that path segments including memory anchors - such as path intersections - were more strongly associated with the pointing error, regardless of when they appeared during encoding. This indicates that the integration of spatial information of a walked path likely begins in the early stages of navigation rather in late stages alone, supporting the parallel hypothesis. Furthermore, theta oscillations in frontal-midline regions during active navigation were related to memory of the path rather than only movement through the path, supporting a mnemonic role of theta oscillations.