The thalamus has long been regarded as a simple relay station, transmitting neural signals from the retina to the cortex to produce image-forming vision. However, recent work from the Liang Lab at the Yale School of Medicine’s Department of Neuroscience demonstrates that the thalamus is an active, selective shaper of motion detection. By integrating inputs from multiple brain regions, the thalamus selectively filters stimuli, refining stimulus information before it is delivered to the cortex.
A key structure in their investigation was the superior colliculus (SC), a midbrain region critical for processing visual stimuli. Beyond the SC’s role in reflexive visual responses, recent data from the Liang Lab demonstrates that the SC provides inputs that actively shape thalamic information processing. The Liang Lab studied how signals from the eye and SC reach the thalamus. Using advanced imaging techniques, they temporarily turned off the midbrain input in mice that were awake to see how this affected the activity and response patterns of different neuron types.
These results showed that inputs from the SC, collicular inputs, were more direction-selective than relayed retinal inputs. At a finer scale, retinal and collicular inputs frequently shared directional preferences, but silencing collicular input reduced motion selectivity, particularly for temporal (horizontal) motion. Inputs from SC neurons had a higher proportion of direction-selective axons than retinal impulses, though both strongly excited thalamic neurons.
This new understanding of the thalamus reveals how distinct brain centers integrate their computational resources to enhance information processing, with implications extending even beyond the visual system. “On the other hand, other research is already suggesting that the convergence between the midbrain and the thalamus is important for detecting sensory inputs, probably overcoming some complex behavioral situation than a very simple one,” said Liang Liang, assistant professor of neuroscience at the Yale School of Medicine and supervising author of the study. “It’s likely that similar behavioral impacts of such convergence also exist for the visual system,” Liang said.
Furthermore, this research might suggest a similar integration of retinal and collicular inputs in other primates. “I’m hoping that this will inspire research in primates and other species. These collicular inputs in the thalamus are present in all the studied mammals so far, including primates, cats, and rabbits,” Liang said. Such work provides more information related to visual processing in the thalamus and might inspire potential new treatments for visual processing-related diseases.
Nevertheless, the Liang Lab’s findings also indicate that there are still many questions about the thalamus, the answers to which may derive a more comprehensive understanding of this structure’s role in visual perception. “There are a lot of other non-retinal inputs, and you should also look at the other non-retinal inputs. How they are organized and what their function is, I think those are other important questions,” said Yue Fei, the study’s leading author. The thalamus is now emerging not as a passive relay, but as an active hub that integrates signals from across the brain to refine visual information.