A new UCLA study has found that as babies develop binocular vision, their brains improve the sense of depth perception through rewiring rather than refining — a very different mechanism than was previously thought to be the standard. Soon after a baby’s eyes open, he or she develops binocular vision that improves considerably during a so-called “critical period” and gives rise to depth perception.
The standard view has been that this improved vision is a result of the brain pruning an overly wired neural circuitry, much the way a sculptor chips away at a chunk of marble to reveal the final form of the sculpture.
In this view, connections laid down in the cortex before birth are then refined and improved by the brain using sensory experience.
However, the UCLA study reveals that more than half of the binocular neurons present at the onset of the critical period do a poor job of encoding visual information. Instead of refining these poorly performing neurons, the brain dismantles their wiring and rebuilds the circuitry with a different set of neurons that are able to “tune” depth perception based on visual feedback.
Researchers Joshua T. Trachtenberg, PhD, and Dario L. Ringach, PhD, professors of neurobiology at the David Geffen School of Medicine at UCLA, and post-doctoral researcher Liming Tan, PhD, tracked cells over the critical period by taking repeated measures of their tuning properties and binocularity. They used a noninvasive microscope in conjunction with genetic manipulations to make cells glow green only when they were active.
In showing that the brain rebuilds its vision circuitry through a different set of neurons, the study findings stand in stark contrast to the predominant view that the brain refines its original tangle of neural wiring to improve binocular vision. That largescale changes in neural circuitry are achieved by controlling a relatively small set of inputs suggests the possibility of specific pathways that can be targeted when developing treatments for neurodevelopmental disorders.
— Elaine Schmidt
Vision Changes the Cellular Composition of Binocular Circuitry During the Critical Period,” Neuron, November 25, 2020