Grid coding, spatial representation, and navigation: Should we assume an isomorphism?

Abstract

Grid cells provide a compelling example of a link between cellular activity and an abstract and difficult to define concept like space. Accordingly, a representational perspective on grid coding argues that neural grid coding underlies a fundamentally spatial metric. Recently, some theoretical proposals have suggested extending such a framework to nonspatial cognition as well, such as category learning. Here, we provide a critique of the frequently employed assumption of an isomorphism between patterns of neural activity (e.g., grid cells), mental representation, and behavior (e.g., navigation). Specifically, we question the strict isomorphism between these three levels and suggest that human spatial navigation is perhaps best characterized by a wide variety of both metric and nonmetric strategies. We offer an alternative perspective on how grid coding might relate to human spatial navigation, arguing that grid coding is part of a much larger conglomeration of neural activity patterns that dynamically tune to accomplish specific behavioral outputs.

Striatal and hippocampal contributions to flexible navigation in rats and humans

“…goal locations on place field over-representation observed in specific paradigms and influence of environmental geometry on grid field integrity (Duvelle et al, 2019;Ekstrom et al, 2020;Krupic et al, 2015;Stachenfeld et al, 2017). It is an interesting future direction for studies to investigate the relationship between neural responses and the internal computations of successor representation shown to account for behaviour flexibility particularly in some spatial navigation tasks (Russek et al, 2017; for review see Momennejad, 2020).…”

An Important Step toward Understanding the Role of Body-based Cues on Human Spatial Memory for Large-Scale Environments

“…We further suggest that these three levels exist in a dynamic interplay in which each level can affect the other levels (see Figure 2). Because of length restrictions, we will refer the interested reader to other articles in which we have discussed these issues in more detail (Ekstrom, Harootonian, & Huffman, 2020;Ekstrom, Huffman, & Starrett, 2017; for a more general discussion, see Poeppel & Adolfi, 2020;Krakauer et al, 2017).…”

Overview of computational models of hippocampus and related structures: Introduction to the special issue

“…The framework of multiple memory systems focused on a role for hippocampus in episodic memory in contrast to the role of neocortical structures in semantic memory. This motivated a range of computational models exploring the mechanisms of episodic memory function in the hippocampus (Hasselmo & Wyble, critique of these theories is presented in the special issue article by Ekstrom, Harootonian, and Huffman (2020). They describe potential pitfalls in extending data on neural representations in a specific task to address a broad scope of behavior.…”

“…Recent theories have proposed that the representations in the hippocampus and associated structures could provide a general framework for understanding representations in semantic memory. A critique of these theories is presented in the special issue article by Ekstrom, Harootonian, and Huffman (). They describe potential pitfalls in extending data on neural representations in a specific task to address a broad scope of behavior.…”

“…Recently research in human subjects has suggested that metric coding similar to grid cells could apply to other cognitive dimensions (Constantinescu, O'Reilly, & Behrens, ). However, as described in the special issue article by Ekstrom et al () these theories may oversimplify the nature of representations for cognitive function, by assuming that neural representations correspond to behavioral representations, when behavior can involve a much broader range of interacting mechanisms and representations.…”