Mental maps without vision: Neural signatures of cognitive maps based on haptic input in the hippocampal formation
The human hippocampus is the key region for forming cognitive maps of our environment. Such a map can support spatial navigation. It is unclear whether this area is similarly involved when an environment is explored with our haptic sense. In this study, we investigated the neural representation of distances on a tactile map in the hippocampal formation, in visually impaired and sighted persons. To this end, 47 participants (22 persons with a visual impairment, PVIs, and 25 sighted controls) performed a navigation task where they learned a tactile city-like map including five item locations. We combined magnetic resonance imaging with adaptation analysis to assess representation of distances between item locations in the hippocampus and entorhinal cortex. Additionally, we assessed cognitive map formation on a behavioural level. We also looked at functional connectivity between navigation-related areas during a subsequent resting-state block. Our data reveal across all participants that the left entorhinal cortex represents distances between locations on a tactile map. Here, we provide the first evidence that maps in the hippocampal formation is preserved when an environment is presented in a non-visual modality. The results also suggest that both PVIs and sighted persons constructed accurate cognitive maps of the tactile environment on a behavioural level. However, early PVIs showed lower performance compared to late PVIs, suggesting an advantage of visual experience. Additionally, we reveal functional connectivity between areas that were involved in the navigation task during a subsequent resting-state block. This might suggest either visual imagination of stimuli during the preceding tasks, or cognitive processes related to our spatial navigation task, which possibly involve replay of stimulus-specific activity.