How the Visual System Develops

This piece, by Onno Berkan, was published on 03/04/25. The original text, by Trägenap et al., was published by Nature Neuroscience on 02/04/25.

This Goethe University study examined how the brain's visual system develops and matures after animals open their eyes and begin experiencing visual input. The scientists studied young ferrets to understand how the brain transitions from its early pre-vision state to reliably processing visual information.

When animals first open their eyes, their visual cortex (the part of the brain that processes vision) already has some basic structure. Still, the visual cortex responds to visual input in an unreliable and inconsistent way. While the brain shows strong responses to visual stimuli at this early stage, these responses vary greatly from viewing to the next, even when looking at the same image.

Within about four days of experiencing normal vision, the brain dramatically improves its ability to process visual information consistently. The researchers found that this improvement involves the brain developing more reliable and stable responses to visual stimuli. This means that when an animal sees the same image multiple times, their brain responds similarly each time, which is essential for reliable vision.

The study revealed this development isn't just about selecting and strengthening existing brain patterns. Instead, the brain undergoes a significant reorganization, creating new patterns of activity that are different from the early responses and the spontaneous activity before eye opening. This process involves changes in how visual information enters the brain (feedforward connections) and how different brain parts communicate (recurrent connections).

Interestingly, when the researchers kept the animals' eyes closed to prevent normal visual experience during the critical development period, the brain failed to develop these responses. This shows that early visual experience is necessary for properly developing the visual system.

This culminated in the "feedforward-recurrent alignment hypothesis," a theory explaining these changes. This hypothesis suggests that reliable vision develops when the incoming visual information properly aligns with the brain's internal communication networks.

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