Summary: The brain’s visual system is a two-way street, but researchers have long debated how the “return lane”—the feedback connections from high-level areas back to low-level ones—is constructed. New research reveals that these connections are not pre-wired or generic; they are “instructive” and physically shaped by early visual experiences.
By raising mice with miniature goggles that limited their sight to specific line orientations, scientists proved that the brain’s wiring directly reflects the specific patterns of the world an individual sees. These feedback loops act as a learned bridge between the “big picture” and fine details, ensuring that our internal neural maps are a bespoke reflection of our unique visual history.
Key Facts
- The “Return Lane”: Feedback connections send abstract, “big picture” information from higher brain regions back to lower areas that process specific edges and shapes.
- Instructive Wiring: The study proves that these connections aren’t just triggered by sight; they are dictated by the specific content of what we see.
- The Goggle Experiment: Mice raised with goggles that biased their world toward specific line orientations developed neural wiring that matched those exact visual patterns.
- Dual-Color Imaging: Researchers used advanced two-photon imaging to measure how feedback inputs from higher visual areas reorganization based on experience.
- Contextual Integration: This wiring allows the brain to use context (like recognizing a table) to help lower areas process specific parts (like a table leg) more efficiently.
Source: Champalimaud Foundation
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.
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 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.
Key Questions Answered:
A: This study suggests that if your early visual experiences were drastically different—for example, if you grew up in a world of only vertical lines—your brain would physically wire itself differently to process those lines. Your neural “map” is a unique record of what you’ve looked at.
A: Because context matters. If your eyes see a brown cylinder, your lower brain might just see “lines.” But if your higher brain knows you’re in a forest, it sends feedback saying “that’s a tree trunk,” helping your lower brain process the details faster and more accurately.
A: While the brain is most plastic during early development (when these “instructive” connections are first formed), this research helps us understand how our environment continues to shape our internal neural architecture.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this visual neuroscience research news
Author: Afonso Vaz Pinto
Source: Champalimaud Foundation
Contact: Afonso Vaz Pinto – Champalimaud Foundation
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Visual experience exerts an instructive role on cortical feedback inputs to the primary visual cortex” by Radhika Rajan, Rodrigo F. Dias, Nikos Malakasis, Margarida Baeta, Xinyun Zhang, Julijana Gjorgjieva, and Leopoldo Petreanu. Current Biology
DOI:10.1016/j.cub.2026.01.031
Abstract
Visual experience exerts an instructive role on cortical feedback inputs to the primary visual cortex
Contextual modulations in the primary visual cortex (V1) critically depend on feedback (FB) connections linking high-order cortical areas with lower-order ones and reflect natural image statistics.
FB projections may encode learned statistical regularities of the environment through their connectivity and tuning, enabling context-dependent modulation of cortical activity.
However, it remains unknown if the properties of FB connections reflect experienced visual statistics.
Here, we used dual-color two-photon imaging to measure the tuning properties and retinotopic organization of inputs from the lateromedial (LM) visual area in layer 1 of V1 in mice reared wearing goggles that limit their visual experience to a narrow range of orientations.
We found that the manipulation biased the orientation tuning and the major axis of the receptive fields of LM inputs toward the experienced orientations. The tuning-dependent retinotopic specificity of FB inputs was different in mice exposed to distinct orientations.
We could recapitulate the effects of goggle rearing in a model in which Hebbian plasticity modifies the synaptic weights of V1 inputs in LM, while those of FB inputs are shaped by anti-Hebbian plasticity.
Our results support an instructive role for visual experience in shaping both the functional properties and the organization of FB inputs and are consistent with the possibility that ascending and descending cortical pathways follow distinct plasticity rules.
They also suggest the circuit mechanisms through which cortical circuits might learn and encode statistical regularities of the environment.
