A new study published in Neuron challenges the notion that the visual thalamus merely acts as a relay station for visual information. Instead, it may integrate additional data from other brain regions and refine this information before sending it to the brain cortex.
NeuronLiang Liang, Ph.D., an assistant professor of neuroscience at Yale School of Medicine (YSM) and senior author of the study, suspected that the thalamus might play a more active role than previously thought.
"Previous studies have discovered that information sent from the retina to the visual thalamus accounts for only about 10% of its total inputs," she explains. "Many of these other inputs originate in different brain regions, but their functions remain largely unknown."
Driven by a broader interest in understanding how the visual system operates and what principles govern information processing in the brain, Liang and her team investigated inputs from the superior colliculus, a midbrain region.
The retina sends signals to multiple brain regions, with two primary recipients: one is the visual thalamus, involved in image formation, and the other is the superior colliculus, which handles reflexive visual responses like ducking or dodging threats.
Intrigued by how these two paths interact at an early stage of processing within the brain, Liang's team monitored signal activity in mice while watching movies. They used genetically encoded indicators to make signaling boutons from retina cells fluoresce green and those from the superior colliculus light up red.
"We found that signals were not randomly integrated but highly organized," explains Liang. "This suggests that during development, connections form deliberately between these two pathways."
Furthermore, similarly functional inputs clustered together, delivering related information to shared thalamic cells. By silencing the superior colliculus inputs, researchers observed suppressed visual responses in thalamic cells and a reduction in motion selectivity.
"Inputs from the superior colliculus actively contribute to movement computation in the thalamus," says Liang. "Extensive processing takes place here, enriching and refining information before it reaches the cortex."
Liang's team now aims to explore additional inputs into the visual thalamus and understand how cells utilize this incoming information.