Extrastriate connectivity of the mouse dorsal lateral geniculate thalamic nucleus

Abstract

The mammalian visual system is one of the most well-studied brain systems. Visual information from the retina is relayed to the dorsal lateral geniculate nucleus of the thalamus (LGd). The LGd then projects topographically to primary visual cortex (VISp) to mediate visual perception. In this view, the VISp is a critical network hub where visual information must traverse LGd-VISp circuits to reach higher order "extrastriate" visual cortices, which surround the VISp on its medial and lateral borders. However, decades of conflicting reports in a variety of mammals support or refute the existence of extrastriate LGd connections that can bypass the VISp. Here, we provide evidence of bidirectional extrastriate connectivity with the mouse LGd. Using small, discrete coinjections of anterograde and retrograde tracers within the thalamus and cortex, our crossvalidated approach identified bidirectional connectivity between LGd and extrastriate visual cortices. We find robust reciprocal connectivity of the medial extrastriate regions with LGd neurons distributed along the "ventral strip" border with the intergeniculate leaflet. In contrast, LGd input to lateral extrastriate regions is sparse, but lateral extrastriate regions return stronger descending projections to localized LGd areas. We show further evidence that axons from lateral extrastriate regions can overlap onto medial extrastriate-projecting LGd neurons in the ventral strip, providing a putative subcortical LGd pathway for communication between medial and lateral extrastriate regions. Overall, our findings support the existence of extrastriate LGd circuits and provide novel understanding of LGd organization in rodent visual system.

Distinct “driving” versus “modulatory” influences of different visual corticothalamic pathways

“…On the other hand, many L6 projections to the rodent pulvinar come from extrastriate areas Scholl et al, 2020;) (Figure 1B), which were not targeted by our injections. Our findings of fundamentally similar "modulatory" influences of V1 L6CTs in the dLGN and pulvinar (from our present inactivation and prior activation studies; Kirchgessner et al, 2020) would lead us to expect that the cumulative effect of L6CT inactivation across cortical areas on the pulvinar would be similar to what we observed in this study in the dLGN (which gets the majority of its L6CT input from V1; Bienkowski et al, 2019;Briggs, 2020) -namely, suppressed spontaneous but not visual activity. Since L6CTs themselves have low spontaneous firing rates (Figure S2C), we attribute their effect on baseline thalamic activity to the high degree of convergence of many L6CTs onto single thalamic cells (Reichova and Sherman, 2004;Sherman, 2016) and to the fact that our recordings were conducted in awake animals as opposed to under anesthesia, which reduces spontaneous firing rates in the thalamus (Durand et al, 2016).…”

An open access mouse brain flatmap and upgraded rat and human brain flatmaps based on current reference atlases

“…The MCP currently encompasses multiple levels of granularity from individual neurons to regional brain circuits. To date, region-level granularity has received most attention (Bienkowski et al, 2018;Bienkowski et al, 2019;Hintiryan et al, 2012;Hintiryan et al, 2016;Zingg et al, 2014;Zingg et al, 2018), and is used here to instantiate the flatmap visualization workflow, using data from a recent study of claustrum connections (Zingg et al, 2018). To generate a brain flatmap representation (here for MsBF1) of the experimental data at the level of gray matter regions, the next step is data aggregation across ARAv1 atlas levels for each gray matter region.…”

“…The MCP currently encompasses multiple levels of granularity from individual neurons to regional brain circuits. To date, region‐level granularity has received most attention (Bienkowski et al, 2018; Bienkowski et al, 2019; Hintiryan et al, 2012; Hintiryan et al, 2016; Zingg et al, 2014; Zingg et al, 2018), and is used here to instantiate the flatmap visualization workflow, using data from a recent study of claustrum connections (Zingg et al, 2018).…”

The mouse cortico-tectal projectome

“…Anatomical tracer data was generated as part of the Mouse Connectome Project (MCP) within the Center for Integrative Connectomics (CIC) at the University of Southern California (USC) Mark and Mary Stevens Neuroimaging and Informatics Institute. MCP experimental methods and online publication procedures have been described previously 23,24,54,73 . We systematically and carefully mapped neuronal connectivity of every cortical structure to determine their input connectivity to the superior colliculus (SC) (for complete injection site list, see Supplementary Table 2).…”