Environmental deformations dynamically shift human spatial memory

Place and grid cells in the hippocampal formation are commonly thought to support a unified and coherent cognitive map of space. This mapping mechanism faces a chal-lenge when a navigator is placed in a familiar environment that has been deformedfrom its original shape. Under such circumstances, many transformations could plau-sibly serve to map a navigator's familiar cognitive map to the deformed space. Previ-ous empirical results indicate that the firing fields of rodent place and grid cellsstretch or compress in a manner that approximately matches the environmentaldeformation, and human spatial memory exhibits similar distortions. These effectshave been interpreted as evidence that reshaping a familiar environment elicits ananalogously reshaped cognitive map. However, recent work has suggested an alter-native explanation, whereby deformation-induced distortions of the grid code areattributable to a mechanism that dynamically anchors grid fields to the most recentlyexperienced boundary, thus causing history-dependent shifts in grid phase. Thisinterpretation raises the possibility that human spatial memory will exhibit similarhistory-dependent dynamics. To test this prediction, we taught participants the loca-tions of objects in a virtual environment and then probed their memory for theselocations in deformed versions of this environment. Across three experiments withvariable access to visual and vestibular cues, we observed the predicted pattern,whereby the remembered locations of objects were shifted from trial to trialdepending on the boundary of origin of the participant's movement trajectory. Theseresults provide evidence for a dynamic anchoring mechanism that governs both neu-ronal firing and spatial memory.