Abstract
Landmarks are critical components of our internal representation of the environment, yet their specific properties are rarely studied, and little is known about how they are processed in the brain. Here we characterised a large set of landmarks along a range of features that included size, visual salience, navigational utility, and permanence. When human participants viewed images of these single landmarks during functional magnetic resonance imaging (fMRI), parahippocampal cortex (PHC) and retrosplenial cortex (RSC) were both engaged by landmark features, but in different ways. PHC responded to a range of landmark attributes, while RSC was engaged by only the most permanent landmarks. Furthermore, when participants were divided into good and poor navigators, the latter were significantly less reliable at identifying the most permanent landmarks, and had reduced responses in RSC and anterodorsal thalamus when viewing such landmarks. The RSC has been widely implicated in navigation but its precise role remains uncertain. Our findings suggest that a primary function of the RSC may be to process the most stable features in an environment, and this could be a prerequisite for successful navigation.
Highlights
The ability to navigate is critical for survival
Space-defining or space ambiguous (SD/SA): Does this item rapidly evoke a sense of surrounding space? (1) Not space-evoking (2) space-evoking
Focusing on a range of landmark attributes, we ascertained that these features were underpinned by two components, which included the permanence of landmarks
Summary
The ability to navigate is critical for survival. As such, there have been decades of research exploring how environments are represented internally, the key components of these representations, and the brain regions that support them. In some theoretical formulations, landmarks are cast as the very building blocks of environmental representations [2,4,5] In others, such as the cognitive map theory, spatial relations between landmarks are regarded as the basis for a critical form of flexible navigation [6,7], while even accounts that emphasise navigation via path integration (i.e. estimating current location based on the movements made since the last known location), acknowledge the role of landmarks in maintaining accuracy [8,9]. Several properties of landmarks have been highlighted as potentially important [12], including the permanence or stability of the landmark (i.e. the likelihood of the landmark being present), its usefulness for navigation (e.g. proximity to a decision point), and its visual features (e.g. size, salience, visibility)
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