A spatial code in the dorsal lateral geniculate nucleus

Abstract

Since their discovery in the early ‘70s1, hippocampal place cells have been studied in numerous animal and human spatial memory paradigms2–4. These pyramidal cells, along with other spatially tuned types of neurons (e.g. grid cells, head direction cells), are thought to provide the mammalian brain a unique spatial signature characterizing a specific environment, and thereby a memory trace of the subject’s place5. While grid and head direction cells are found in various brain regions, only few hippocampal-related structures showing ‘place cell’-like neurons have been identified6,7, thus reinforcing the central role of the hippocampus in spatial memory. Concurrently, it is increasingly suggested that visual areas play an important role in spatial cognition as recent studies showed a clear spatial selectivity of visual cortical (V1) neurons in freely moving rodents8–10. We therefore thought to investigate, in the rat, such spatial correlates in a thalamic structure located one synapse upstream of V1, the dorsal Lateral Geniculate Nucleus (dLGN), and discovered that a substantial proportion (ca. 30%) of neurons exhibits spatio-selective activity. We found that dLGN place cells maintain their spatial selectivity in the absence of visual inputs, presumably relying on odor and locomotor inputs. We also found that dLGN place cells maintain their place selectivity across sessions in a familiar environment and that contextual modifications yield separated representations. Our results show that dLGN place cells are likely to participate in spatial cognition processes, creating as early as the thalamic stage a comprehensive representation of one given environment.

Spatial modulation of visual signals arises in cortex with active navigation

“…However, our mice were head restrained and hence lacked vestibular inputs (Ravassard et al, 2013;Russell et al, 2006). Perhaps when mice freely move, LGN does show some spatial modulation (Hok et al, 2018), which is possibly amplified in V1 by non-linear mechanisms (Chariker et al, 2016;Lien and Scanziani, 2013). Navigational signals affected all cortical visual areas approximately equally, consistent with the widespread neural coding of task-related information across the posterior cortex (Koay et al, 2019;Minderer et al, 2019).…”

“…Spatial signals might enter the visual pathway upstream of V1, in the lateral geniculate nucleus (LGN). Indeed, spatial signals have been seen elsewhere in thalamus (Jankowski et al, 2015;Taube, 1995) and possibly also in LGN itself (Hok et al, 2018). Spatial signals might also become stronger downstream of V1, in higher visual areas.…”

A compact spatial map in V2 visual cortex

“…The dLGN, being the one synapse upstream structure of the V1, displays place cells (Hok et al, 2018).…”

Spatial modulation of visual responses arises in cortex with active navigation

“…Spatial signals might enter the visual pathway upstream of V1, in the lateral geniculate nucleus (LGN). Indeed, spatial signals have been seen elsewhere in thalamus ( Jankowski et al, 2015 ; Taube, 1995 ) and possibly also in LGN itself ( Hok et al, 2018 ). Spatial signals might also become stronger downstream of V1, in higher visual areas (HVAs).…”