Abstract
SummaryA key task for the visual system is to combine spatially overlapping representations of the environment, viewed by either eye, into a coherent image. In cats and primates, this is accomplished in the cortex [1], with retinal outputs maintained as separate monocular maps en route through the lateral geniculate nucleus (LGN). While this arrangement is also believed to apply to rodents [2, 3], this has not been functionally confirmed. Accordingly, here we used multielectrode recordings to survey eye-specific visual responses across the mouse LGN. Surprisingly, while we find that regions of space visible to both eyes do indeed form part of a monocular representation of the contralateral visual field, we find no evidence for a corresponding ipsilateral representation. Instead, we find many cells that can be driven via either eye. These inputs combine to enhance the detection of weak stimuli, forming a binocular representation of frontal visual space. This extensive thalamic integration marks a fundamental distinction in mechanisms of binocular processing between mice and other mammals.
Highlights
To help distinguish between dorsal LGN (dLGN) and IGL/vLGN recordings, we performed a subset of these (n = 27; 36 electrode placements) in Opn4+/tau-lacZ mice [6, 7] in which the IGL is readily detected by b-galactosidase staining (Figure S1A and S1B available online)
Given the substantial binocular integration that we describe here, one might expect that monocular lateral geniculate nucleus (LGN) cells would receive input from regions of space visible to only the contralateral eye
While there is no purely ipsilateral representation of binocular visual space, a contralateral-only representation is present within the mouse LGN
Summary
Based upon published anatomy [2, 3], we expected to find individual neurons responsive to either the contralateral or ipsilateral eye in the mouse dorsal LGN (dLGN; primary thalamocortical relay). The relative magnitude of responses to stimulation of either eye varied for binocular cells (Figures 1A and 1B), but latencies were typically very similar, suggesting a direct convergence of ipsilateral/contralateral retinal ganglion cells (RGCs) onto the same LGN neuron. We observed many LGN neurons (n = 107) with contralateral-driven responses whose activity was modulated by bright stimuli presented to the ipsilateral eye (Figures 1F– 1H).
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