The visual system is hierarchically organised into different areas. The lower visual areas see small parts of the visual field, and they are sensitive to very simple features, such as edges and their orientation. Higher up the hierarchy, the visual areas start encoding more abstract representations of the world, expanding their visual field to respond to stimuli such as objects and faces.
At the same time, the areas that see "the big picture" send back information to the lower visual areas, called "feedback" connections. Feedback connections are considered essential for integrating contextual information, namely by providing information to lower visual areas about the broader scene, rather than just the small, specific part of the image they are looking at.
For example, a neuron in a higher visual area that responds to tables would send feedback to a neuron in a lower level area that encodes just a part of the table, such as its legs.
However, surprisingly, neurons in higher visual areas of the brain can also sometimes send back information to neurons in lower visual areas that have nothing to do with tables.
But do feedback connections reflect relationships between the "parts" and the "whole " learned from experience?, asks Leopoldo Petreanu, principal investigator of the Champalimaud Foundation's Cortical Circuits lab.
In a previous study in mice, Petreanu and his team had shown that the organization of feedback connections depended on having visual experience. (https://www.fchampalimaud.org/news/pink-elephants-brain-how-experience-shapes-neural-connectivity)
To do this, they compared the feedback connections in normal mice with those in mice reared in the dark, and found that in the second case, due to the lack of visual experience, the organization of the feedback connections was disrupted. This showed that the organisaton of feedback depended on experience, consistent with the hypothesis that it might reflect a learned relation between the big picture, encoded in high-order areas, and the lower-order features, encoded in the lower areas.
But one thing that was still not clear was whether this organization is passive or what the researchers call "instructive". In other words, does any experience just trigger the same organization of feedback connections, or do different experiences result in different neural wiring? A new study by the same team, published today (11/02/2026) in the journal Current Biology, aimed at tackling this question.
Another way to phrase the issue is to ask whether feedback connections wire themselves to specific, content-related subsets of neurons in lower visual areas, or whether they do so generically, independently of context. The new study shows that these connections do, in fact, play an instructive role. Their organization is not generic.
Mice with little goggles
To show this, the researchers reared mice fitted with miniature goggles that biased their perception of the visual world. One group of animals only saw edges oriented at a certain angle, while the other saw edges oriented at a different angle. "For some mice, the world looked like elongated lines in some direction, and for the other, it also looked elongated, but in a different way", says Petreanu.
Using a microscopy technique called dual-color two photon imaging, first co-authors Radhika Rajan and Rodrigo Dias measured the tuning properties and the organisation of feedback inputs from a higher visual area back to a lower one.
What they found is that the animals with different visual experiences had very different tuning properties and patterns of organisation in these feedback connections, shaped by what they had seen since birth. "The feedback connections reflected the visual experience of the mice, supporting the idea that these connections capture associations between visual features, represented in different areas, formed through experience", says Petreanu.
