A new study published in Nature Communications shows how the brain of young mice changes to develop clear vision. The brain’s visual system, which processes what we see, isn’t fully set at birth. Instead, it adjusts based on what the eyes see early in life. The visual cortex, the brain area that handles vision, refines itself during a key time called the critical period. This study is the first to watch this process in real-time in mice, revealing how connections in the brain form and disappear to create better vision.
The researchers looked at neurons and focused on dendrites, the branch-like parts of neurons that connect to other cells. On these dendrites, tiny structures called spines hold synapses, the points where neurons connect. Over 10 days, the scientists tracked hundreds of spines in the visual cortex of young mice. They found that only 40 percent of the spines present at the start were still there by the end. This shows that the brain adds and removes many connections to improve binocular vision, which is the ability to combine images from both eyes.
Extensive changes in connections
The mice watched patterns of black and white lines moving in different directions. The researchers checked the spines on day 1, day 5, and day 10 of the critical period. About one-third of the spines from day 1 were gone by day 5, and new ones appeared. The same pattern happened between day 5 and day 10. They also noticed that most neurons that responded to the patterns at first stopped responding by the end, possibly because they started handling different tasks.
The study found rules for which spines lasted. Spines that were more active and matched the neuron’s preferred line direction were more likely to stay. Spines that responded to both eyes were more active and survived more often than those responding to just one eye. This supports the idea that connections used more often are kept, while unused ones are removed. The researchers also saw that spines close to each other on the dendrite often worked together, forming clusters that strengthened their signals. Using a computer model, they confirmed that these rules explain how the brain refines vision.