The Brain's Balancing Act: How Vision and Movement Intertwine in the Mind's Eye
Every time you glance around a room, your eyes, ears, and brain work together in ways you never notice. The world seems stable, yet your head is constantly in motion. How does your brain stop everything from appearing to spin? An international team of researchers explored how the brain keeps our visual world steady even as we move through it.
Published in Proceedings of the National Academy of Sciences (PNAS), the paper “Inter- and Intrahemispheric Sources of Vestibular Signals to V1” was co-authored by Nicolas Brunel (Professor of Computational Neuroscience in the Department of Computing Sciences, Bocconi University) and Alessandro Sanzeni (also in the Department of Computing Sciences, Bocconi), together with Guy Bouvier (Department of Physiology & HHMI, University of California, San Francisco; CNRS/Université Paris-Saclay), Elizabeth Hamada (Department of Neurology, University of California, San Francisco), and Massimo Scanziani (Department of Physiology & HHMI, University of California, San Francisco). Together, the team uncovers the hidden neural pathways that carry signals from the vestibular system—the inner ear’s motion sensors—to the primary visual cortex (V1), the brain’s gateway to sight.
“We found that two distinct pathways deliver head motion signals to the primary visual cortex: the pulvinar nucleus of the thalamus and the contralateral visual cortex,” the authors write. These two routes, they explain, provide complementary directional information about head movements, revealing how the brain blends sensory inputs to maintain stable vision during motion.
Seeing motion beyond the eyes
The researchers recorded neural activity in the visual cortex of mice as their heads rotated clockwise and counterclockwise in darkness. What they found was striking: even without visual input, neurons in V1 fired in patterns that mirrored the animals’ head movements. The deeper layers of V1 carried particularly rich representations of these movements. Using computational decoding techniques, the team showed that direction and speed could be predicted with over 99.5% accuracy from the firing patterns of a few hundred neurons.
To identify where these signals come from, the scientists traced connections through the brain. They discovered that one major pathway originates in the pulvinar, a thalamic hub that receives vestibular information from the deep cerebellar nuclei (DCN). In elegant experiments combining pharmacological and optogenetic methods, they demonstrated that silencing the pulvinar sharply reduced V1 responses to head movement, especially for rotations opposite the silenced hemisphere. As the paper notes, “Silencing the pulvinar greatly reduced V1 responses to head rotations contraversive to the silenced hemisphere” (p. 3). This revealed that the pulvinar carries a contraversive bias—for example, clockwise movement signals sent to the left V1.
A second, subtler source of motion information came from the opposite visual cortex, transmitted through callosal connections between the hemispheres. This interhemispheric pathway contributed information about rotations in the opposite direction, balancing the visual system’s encoding of head motion.
Mapping the brain's motion code
By combining mathematical models, multi-neuron recordings, and viral tracing, Brunel and colleagues showed that V1 population dynamics reflect not only direction and speed, but also acceleration and even the memory of previous movements lasting several seconds.
In the authors’ words, “taken together, these results show that mouse V1, and especially its deeper layers, encodes a rich representation of head movement that can be accessed to simultaneously decode both present and past movements with high precision.”
Challenging the Traditional Views
This discovery challenges the traditional view of V1 as a purely visual area. Instead, it portrays the early visual cortex as a multimodal hub where sensory and motor information converge. By revealing the brain’s internal code for motion, the research opens new perspectives on balance disorders, virtual reality adaptation, and even artificial vision systems. After all, to see the world clearly, our brains must first know where we are moving within it.
