Abstract
SUMMARYMotion/direction-sensitive and location-sensitive neurons are the two major functional types in mouse visual thalamus that project to the primary visual cortex (V1). It is under debate whether motion/direction-sensitive inputs preferentially target the superficial layers in V1, as opposed to the location-sensitive inputs, which preferentially target the middle layers. Here, by using calcium imaging to measure the activity of motion/direction-sensitive and location-sensitive axons in V1, we find evidence against these cell-type-specific laminar biases at the population level. Furthermore, using an approach to reconstruct axon arbors with identified in vivo response types, we show that, at the single-axon level, the motion/direction-sensitive axons project more densely to the middle layers than the location-sensitive axons. Overall, our results demonstrate that motion/direction-sensitive thalamic neurons project extensively to the middle layers of V1 at both the population and single-cell levels, providing further insight into the organization of thalamocortical projection in the mouse visual system.
Highlights
In mammalian visual systems, functionally specific thalamocortical projections from the dorsal lateral geniculate nucleus to the primary visual cortex (V1) serve as the major feedforward inputs for cortical computation
Besides cells with classical spatial receptive fields (RFs) that are sensitive to stimulus location (Grubb and Thompson, 2003; Denman and Contreras, 2016), a significant portion of the cells in mouse dorsal lateral geniculate nucleus (dLGN) are sensitive to motion direction (Marshel et al, 2012; Piscopo et al, 2013; Zhao et al, 2013; Durand et al, 2016; Suresh et al, 2016; Roman Roson et al, 2019)
One current view is that the motion/ direction-sensitive cells, resembling the W cells in cats, preferentially project to the superficial layers, in contrast to the location-sensitive (LS) cells, which have a middle layer bias, resembling the X/Y cells in cats (Cruz-Martın et al, 2014; for a review, see Seabrook et al, 2017)
Summary
Functionally specific thalamocortical projections from the dorsal lateral geniculate nucleus (dLGN) to the primary visual cortex (V1) serve as the major feedforward inputs for cortical computation. Besides cells with classical spatial receptive fields (RFs) that are sensitive to stimulus location (Grubb and Thompson, 2003; Denman and Contreras, 2016), a significant portion of the cells in mouse dLGN are sensitive to motion direction (Marshel et al, 2012; Piscopo et al, 2013; Zhao et al, 2013; Durand et al, 2016; Suresh et al, 2016; Roman Roson et al, 2019) How these motion/direction-sensitive dLGN cells project to V1 is not fully understood. The evidence for this laminar specificity is scarce and controversial: Whereas one study found, in support of this view, that the middle layers in V1 receive slightly less direction-sensitive inputs from the dLGN than the superficial layers (Kondo and Ohki, 2016), another study found contradictory evidence that middle and superficial layers receive similar amounts of direction-sensitive inputs from the dLGN (Sun et al, 2016)
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