When navigation requires travelling along familiar habitual route

When navigation requires travelling along familiar habitual routes evidence indicates that stimulus–response

associations stored in the dorsal striatum allow an animal to determine in which direction to proceed and when they have travelled far enough to arrive at the goal 1, 2 and 3]. However, when navigation relies on determining self-location in the environment and computing the spatial relationship to the goal, the hippocampus and connected structures of the medial temporal lobe (MTL), such as the entorhinal cortex, are needed for navigation 4, 5, 6, 7 and 8]. MTL and striatum also operate as BGB324 part of a wider brain network serving navigation. In summary, it is thought the parahippocampal cortex supports the recognition of specific views and the retrosplenial cortex converts between allocentric (environment-bound) representations in hippocampal–entorhinal regions to egocentric representations in posterior parietal cortex 9•, 10 and 11]. In addition, the prefrontal cortex is thought to aid route planning, decision-making and switching between navigation NU7441 strategies 12 and 13] and the cerebellum is required when navigation involves monitoring self-motion [14]. Here we focus on the role of the hippocampus and entorhinal cortex because of recent discoveries from functional magnetic resonance imaging (fMRI) and single unit recording

studies and the development of new computational models. Electrophysiological investigations have revealed several distinct neural representations of self-location (see Figure 1 and for review [15]). Briefly, place cells found in hippocampal regions CA3 and CA1 signal the animal’s presence in particular regions of space; the cells’ place fields [16] (Figure 1a). Place fields are broadly stable between visits to familiar locations but remap whenever a novel environment is encountered, STK38 quickly forming a new and distinct representation 17 and 18]. Grid cells, identified in entorhinal

cortex, and subsequently in the pre-subiculum and para-subiculum, also signal self-location but do so with multiple receptive fields distributed in a striking hexagonal array 19 and 20] (Figure 1b). Head direction cells, found throughout the limbic system, provide a complementary representation, signalling facing direction; with each cell responding only when the animal’s head is within a narrow range of orientations in the horizontal plane (e.g. [21], Figure 1c). Other similar cell types are also known, for example border cells which signal proximity to environmental boundaries [22] and conjunctive grid cells which respond to both position and facing direction [23]. It is likely that these spatial representations are a common feature of the mammalian brain, at the very least grid cells and place cells have been found in animals as diverse as bats, humans, and rodents [15].

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