Neuron
Volume 96, Issue 2, 11 October 2017, Pages 330-338.e5
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Functional Convergence at the Retinogeniculate Synapse

https://doi.org/10.1016/j.neuron.2017.09.037Get rights and content
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Highlights

  • Optogenetic analysis of convergence of RGCs in visual thalamus

  • On average, ten RGCs functionally innervate mouse dLGN thalamocortical neurons

  • 30% of functional RGC inputs dominate thalamic neuron activity; the remainder are weak

  • Results reconcile connectomics with functional estimates of convergence

Summary

Precise connectivity between retinal ganglion cells (RGCs) and thalamocortical (TC) relay neurons is thought to be essential for the transmission of visual information. Consistent with this view, electrophysiological measurements have previously estimated that 1–3 RGCs converge onto a mouse geniculate TC neuron. Recent advances in connectomics and rabies tracing have yielded much higher estimates of retinogeniculate convergence, although not all identified contacts may be functional. Here we use optogenetics and a computational simulation to determine the number of functionally relevant retinogeniculate inputs onto TC neurons in mice. We find an average of ten RGCs converging onto a mature TC neuron, in contrast to >30 inputs before developmental refinement. However, only 30% of retinogeniculate inputs exceed the threshold for dominating postsynaptic activity. These results signify a greater role for the thalamus in visual processing and provide a functional perspective of anatomical connectivity data.

Keywords

visual system
optogenetics
synapse refinement
mouse
dorsal lateral geniculate nucleus
synaptic strength
synaptic physiology
connectomics

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