New Study Reveals Visual Thalamus Plays a Larger Role in Visual Processing Than Previously Believed

A recent study published in Neuron has revealed that the visual thalamus, long thought to serve primarily as a relay station for visual information, plays a more complex and dynamic role in visual processing. The research demonstrates that this brain region not only transmits signals from the retina but also integrates and reshapes visual information by incorporating inputs from other areas of the brain.

Rethinking the Role of the Visual Thalamus

Traditionally, the visual thalamus has been viewed as a passive conduit, channeling visual signals from the eye to the visual cortex. However, Liang Liang, Ph.D., assistant professor of neuroscience at Yale School of Medicine and senior author of the study, questioned this assumption.

“Previous studies have found that information sent to the visual thalamus from the retina only accounts for around 10% of its total inputs,” Dr. Liang explains. “There are many from several other brain regions, but their roles have been largely mysterious.”

Driven by an interest in uncovering how the visual system processes information, Liang and her team focused on a specific brain region known as the superior colliculus, which also receives input from the retina and is known to coordinate reflexive visual behaviors, such as avoiding oncoming objects.

Mapping Interactions Between Visual Pathways

The retina sends visual data to two primary brain regions: the visual thalamus, which is essential for image formation, and the superior colliculus, which handles reflexive responses. The fact that both receive retinal inputs and appear to interact intrigued the researchers.

To study this interaction, the team used genetically encoded indicators in mice. They labeled the ends of retinal cells (called boutons) with a green, fluorescent marker and superior colliculus boutons with a red marker. This allowed them to observe how both pathways behaved in real time while the mice were exposed to visual stimuli, such as watching movies.

Their findings revealed a surprising level of organization. The inputs from both regions did not randomly interact but were deliberately structured. "That means that the brain really makes an effort to wire them together during development," Liang noted.

Moreover, inputs with similar signal properties clustered together and connected to the same thalamic neurons, suggesting a purposeful convergence of information.

Motion Processing Begins in the Thalamus

To further explore how this convergence impacts visual processing, the team silenced the input from the superior colliculus. This intervention suppressed the amplitude of the thalamic cells’ responses and significantly reduced motion selectivity, particularly in neurons tuned to detect specific directions of movement.

This led Liang to conclude that the superior colliculus does more than relay visual information, it actively contributes to the computation of motion within the thalamus. “There’s substantial computation going on to enrich and selectively enhance visual information before it even gets to the cortex,” she said.

Next Steps in Visual System Research

Building on these findings, the research team is now turning its attention to other non-retinal inputs to the visual thalamus. Their goal is to determine how these pathways may also shape visual processing.

“We're also looking at the cells that receive information from these inputs,” said Yue Fei, Ph.D., lead author of the study and recent graduate of Liang’s lab. “We want to see how they make use of that information.”

Reference:

Yue Fei et al, Coordination of distinct sources of excitatory inputs enhances motion selectivity in the mouse visual thalamus, Neuron (2025). DOI: 10.1016/j.neuron.2025.07.015