Uncovering the Role of Colliculogeniculate Input for Thalamic Visual Processing

Date of Award

Spring 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Interdepartmental Neuroscience Program

First Advisor

Liang, Liang

Abstract

The primary visual thalamus, known as the dorsolateral geniculate nucleus (dLGN) of the thalamus, serves as the gateway for visual signals to reach the visual cortex. In addition to receiving diverse channels of input from retinal ganglion cells, the dLGN is also innervated by the midbrain superior colliculus. The highly conserved colliculogeniculate axons possess several synaptic properties that resemble those of retinogeniculate axons, including comingling axonal boutons on proximal dendrites of dLGN neurons and providing strong excitatory synaptic input that can elicit neural firing in target neurons. However, it remains unclear how collicular input combines with retinal input to reinforce or broaden channels of visual information in their target dLGN neurons. Using chronic deep-brain dual-color two-photon calcium imaging, we simultaneously recorded visual responses from hundreds of collicular and retinal axonal boutons in the thalamus of awake, head-restrained mice. We observed that collicular axons also exhibited diverse visual response properties and similar coarse retinotopic organizations as retinal axons. On a spatial scale of approximately 6 μm, nearby collicular boutons shared one or several feature preferences in common, following similar fine-scale functional arrangements as retinal boutons. Notably, neighboring collicular and retinal boutons showed similar preferences for visual features, suggesting that the two distinct sources of inputs may work in synergy. Finally, inhibiting excitatory collicular input resulted in suppression of visual responses in the majority of impacted dLGN neurons. While silencing collicular input reduced response magnitudes subtractively or divisively in subsets of dLGN neurons, it also selectively reduced direction selectivity in a significant fraction of dLGN neurons. Specifically, a subset of dLGN neurons lost their preference for the nasal-to-temporal direction of motion. In summary, these findings suggest that functionally specific convergence between collicular and retinal inputs can already reinforce select channels of motion signals prior to the cortex. Our findings also shed light on how distinct streams of excitatory driver-like inputs coordinate at multiple levels to impact neural computation.

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