A surge in brain connections fine-tunes visual responses within days of eyes opening, study finds

by Max Planck Florida Institute for Neuroscience

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Our brain's wiring is shaped both by genes and what we experience, and the visual system is a great model for studying how the two work together. Before the eyes ever open, genetic programs lay down a first draft of the brain's visual circuits. But once they open, experience takes over, with visual information refining the initial draft.

At first, neurons in the primary visual cortex, an area critical for vision, respond broadly to different visual features and receive signals from the two eyes that don't yet match. However, over the days that follow, these responses become sharply tuned to specific visual features, and the signals from the two eyes align, key refinements for mature vision.

Scientists have long thought that this refinement happens mainly through pruning: the brain keeps the connections that carry useful signals and eliminates the rest. But that picture leaves something out. In a newly published study in Current Biology, researchers in MPFI's Fitzpatrick lab show that in the days immediately after the onset of visual experience, neurons gain many new connections that drive early visual circuit refinement.

"Visual experience really kicks off a dramatic remodeling of neural circuitry that leads to mature vision," says Dr. Juliane Jaepel, one of the lead authors of the study. "We found that neurons gain nearly five times as many excitatory synaptic connections immediately following the onset of experience, and we wanted to know what all these connections contribute and how they change the way neurons respond."

Mapping inputs as vision begins

To understand this remodeling, Jaepel and co-lead author Dr. Clara Tepohl mapped the visual information these neurons receive at eye opening and after several days of visual experience. Connections form at tiny protrusions on a neuron's branches called dendritic spines. The scientists painstakingly recorded the information a single neuron received at hundreds of these spines.

By showing visual patterns to each eye separately, they determined whether each spine responded to the left eye, the right eye or both. They also mapped which visual features each spine responded to most strongly and whether spines that responded to similar features were arranged next to one another along the neuron's branches. By comparing spine maps before and after several days of visual experience, the team could determine how the information these neurons receive changes during early vision.

Growth favors well-matched connections

They found that during the first few days of visual experience, the number of spines on the neurons expanded nearly fivefold. However, this expansion was far from random. Rather, specific types of information became much more common. Connections that responded selectively to edges of a particular orientation, a basic building block of vision, expanded much more than connections responding to all orientations alike. Likewise, the number of connections that showed selective responses to the same edge orientation shown to both eyes increased dramatically.

The scientists also found that after visual experience, connections responding to edges of similar orientation tended to be localized next to each other on the neuron, an organization that strengthens their combined signal. In other words, neurons sharpened their responses in the early days after eye opening primarily by adding many more well-matched connections rather than pruning away poorly matched ones.

A broader model of circuit development

"These findings provide new insights into how the earliest stages of visual experience dramatically reshape the brain's circuitry," says Dr. David Fitzpatrick, senior author of the study. "As visual experience begins, neurons expand and reorganize their network of synaptic connections, building on an existing scaffold and refining the patterns of connections that individual neurons receive to support more coherent and robust visual responses."

The research team thinks this early experience-driven rewiring process could be a fundamental principle of neural circuit development that applies beyond visual circuits. This expansion-based refinement may be relevant to the many circuits where experience shapes the integration of different information to generate sensation, cognition and behavior. Future work to fully explore the mechanisms behind these highly dynamic early episodes of circuit growth and refinement could open the door to understanding how disruption of these mechanisms may contribute to developmental brain disorders.

Publication details

Juliane Jaepel et al., Functional recomposition of excitatory synaptic inputs to individual neurons in ferret visual cortex after the onset of visual experience, Current Biology (2026). DOI: 10.1016/j.cub.2026.09.026

Journal information: Current Biology

Key medical concepts

Dendritic SpinesPrimary Visual Cortex

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Neurology Provided by Max Planck Florida Institute for Neuroscience Who's behind this story?

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