Damage to the medial temporal lobes produces profound amnesia, greatly impairing the ability of patients to learn about new associations and events. While studies in rodents suggest a strong link between damage to the hippocampus and the ability to navigate using distal landmarks in a spatial environment, the connection between navigation and memory in humans remains less clear. Past studies on human navigation have provided mixed findings about whether patients with damage to the medial temporal lobes can successfully acquire and navigate new spatial environments, possibly due, in part, to issues related to patient demographics and characterization of medial temporal lobe damage. Here, we report findings from a young, high functioning patient who suffered severe medial temporal lobe damage. Although the patient is densely amnestic, her ability to acquire and utilize new, but coarse, spatial “maps” appears largely intact. Specifically, a novel computational analysis focused on the precision of her spatial search revealed a significant deficit in spatial precision rather than spatial search strategy. These findings argue that an intact hippocampus in humans is not necessary for representing multiple external landmarks during spatial navigation of new environments. We suggest instead that the human hippocampus may store and represent complex high-resolution bindings of features in the environment as part of a larger role in perception, memory, and navigation.

Increasing evidence suggests that the human hippocampus contributes to a range of different behaviors, including episodic memory, language, short-term memory, and navigation. A novel theoretical framework, the Precision and Binding Model, accounts for these phenomenon by describing a role for the hippocampus in high-resolution, complex binding. Other theories like Cognitive Map Theory, in contrast, predict a specific role for the hippocampus in allocentric navigation, while Declarative Memory Theory predicts a specific role in delay-dependent conscious memory. Navigation provides a unique venue for testing these predictions, with past results from research with humans providing inconsistent findings regarding the role of the human hippocampus in spatial navigation. Here, we tested five patients with lesions primarily restricted to the hippocampus and those extending out into the surrounding medial temporal lobe cortex on a virtual water maze task.Consistent with the Precision and Binding Model, we found partially intact allocentric memory in all patients, with impairments in the spatial precision of their searches for a hidden target. We found similar impairments at both immediate and delayed testing. Our findings are consistent with the Precision and Binding Model of hippocampal function, arguing for its role across domains in high-resolution, complex binding.Significance Statement: Remembering goal locations in one's environment is a critical skill for survival. How this information is represented in the brain is still not fully understood, but is believed to rely in some capacity on structures in the medial temporal lobe. Contradictory findings from studies of both humans and animals have been difficult to reconcile with regard to the role of the MTL, specifically the hippocampus. By assessing impairments observed during navigation to a goal in patients with medial temporal lobe damage we can better understand the role these structures play in such behavior. Utilizing virtual reality and novel analysis techniques, we have more precisely assessed the impact that medial temporal lobe damage has on spatial memory and navigation. wileyonlinelibrary.com/journal/hipo

We offer novel evidence that a Black man appears lighter in the mind’s eye following a counter-stereotypic prime, a phenomenon we refer to as skin tone memory bias. In Experiment 1, participants were primed subliminally with the counter-stereotypic word educated or with the stereotypic word ignorant, followed by the target stimulus of a Black man’s face. A recognition memory task for the target’s face and six lures (skin tone variations of ±25%, ±37%, and ±50%) revealed that participants primed with “educated” exhibited more memory errors with respect to lighter lures—misidentifying even the lightest lure as the target more often than counterparts primed with “ignorant.” This skin tone memory bias was replicated in Experiment 2. We situate these findings in theorizing on the mind’s striving for cognitive consistency. Black individuals who defy social stereotypes might not challenge social norms sufficiently but rather may be remembered as lighter, perpetuating status quo beliefs.

Research into the behavioral and neural correlates of spatial cognition and navigation has benefited greatly from recent advances in virtual reality (VR) technology. Devices such as head-mounted displays (HMDs) and omnidirectional treadmills provide research participants with access to a more complete range of body-based cues, which facilitate the naturalistic study of learning and memory in three-dimensional (3D) spaces. One limitation to using these technologies for research applications is that they almost ubiquitously require integration with video game development platforms, also known as game engines. While powerful, game engines do not provide an intrinsic framework for experimental design and require at least a working proficiency with the software and any associated programming languages or integrated development environments (IDEs). Here, we present a new asset package, called Landmarks, for designing and building 3D navigation experiments in the Unity game engine. Landmarks combines the ease of building drag-and-drop experiments using no code, with the flexibility of allowing users to modify existing aspects, create new content, and even contribute their work to the open-source repository via GitHub, if they so choose. Landmarks is actively maintained and is supplemented by a wiki with resources for users including links, tutorials, videos, and more. We compare several alternatives to Landmarks for building navigation experiments and 3D experiments more generally, provide an overview of the package and its structure in the context of the Unity game engine, and discuss benefits relating to the ongoing and future development of Landmarks.

1Studies in rodents have demonstrated that transecting the white matter pathway 2 linking the hippocampus and anterior thalamic nuclei -the fornix -impairs flexible 3 navigational learning in the Morris Water Maze (MWM), as well as similar spatial 4 learning tasks. While diffusion MRI studies in humans have linked fornix 5 microstructure to scene discrimination and memory, its role in human navigation is 6 currently unknown. We used high-angular resolution diffusion MRI to ask whether 7 inter-individual differences in fornix microstructure would be associated with spatial 8 learning in a virtual MWM task. To increase sensitivity to individual learning across 9 trials, we adopted a novel curve fitting approach to estimate a single index of 10 learning rate. We found a significant correlation between learning rate and the 11 microstructure (mean diffusivity) of the fornix, but not that of a control tract linking 12 occipital and anterior temporal cortices (the inferior longitudinal fasciculus, ILF). 13Further, this correlation remained significant when controlling for hippocampal 14 volume. These findings extend previous animal studies by demonstrating the 15 functional relevance of the fornix for human navigational learning, and highlight the 16 importance of a distributed neuroanatomical network, underpinned by key white 17 matter pathways, such as the fornix, in complex spatial behaviour. 18 19