Ferret brain study explores how reliable visual representations emerge during development

Brain circuits are known to gradually form and develop after birth as the result of both innate biological processes and life experiences. Past studies suggest that the initial development of brain circuits spans across two different stages.

The first of these stages takes place before animals and humans start experiencing life. During this stage, the initial organization of cortical networks is established via internal (i.e., endogenous) mechanisms.

Following the formation of this initial organization, the second stage begins. This second phase entails the refinement of cortical networks over time in response to an animal or human’s individual life experiences.

Researchers at the Frankfurt Institute for Advanced Studies (FIAS), Goethe University Frankfurt and the Max Planck Florida Institute for Neuroscience recently explored the processes supporting the early development of neural circuits in the mammal brain’s visual cortex. Their paper, published in Nature Neuroscience, unveils patterns of cortical activity occurring in the ferret visual cortex before and after newly born pups first open their eyes.

“The fundamental structure of cortical networks arises early in development before the onset of sensory experience,” Sigrid Trägenap, David E. Whitney and their colleagues wrote in their paper. “However, how endogenously generated networks respond to the onset of sensory experience and how they form mature sensory representations with experience remain unclear. We examined this ‘nature–nurture transform’ at the single-trial level using chronic in vivo calcium imaging in ferret visual cortex.”

To better understand what happens in the visual cortex of ferrets before and after birth, the researchers used a technique called in vivo calcium imaging. This imaging approach relies on the use of special dyes or genetically encoded proteins that light up when calcium levels increase, which in neurons occurs when they become active.

Trägenap, Whitney and their colleagues used calcium imaging to record the activity of neurons in the ferret’s visual cortex before ferret pups first opened their eyes, when they first opened their eyes, and a week after they were born. Interestingly, they observed different patterns of activity at these different stages of early development.

“At eye opening, visual stimulation evokes robust patterns of modular cortical network activity that are highly variable within and across trials, severely limiting stimulus discriminability,” wrote Trägenap, Whitney and their colleagues.

“These initial stimulus-evoked modular patterns are distinct from spontaneous network activity patterns present before and at the time of eye opening. Within a week of normal visual experience, cortical networks develop low-dimensional, highly reliable stimulus representations that correspond with reorganized patterns of spontaneous activity.”

Overall, the results of this recent study suggest that activity in the visual cortex of ferrets, and potentially other mammals, varies significantly before, during and after birth. Their observations indicate that when a ferret first opens its eyes, its brain struggles to create consistent representations of what the animal first sees.

After just a week of life, however, the same ferret’s brain activity shifts. They observed stable neural patterns linked to representations of visual stimuli. As part of their study, the researchers also developed a computational model that they used to artificially replicate the early development processes they observed.

“Using a computational model, we propose that reliable visual representations derive from the alignment of feedforward and recurrent cortical networks shaped by novel patterns of visually driven activity,” wrote the researchers.

Based on their findings, Trägenap, Whitney and their colleagues suggest that visual representations emerge as the result of two types of cortical networks, one carrying incoming sensory signals (i.e., feedforward) and one refining visual representations via internal processes (i.e., recurrent). Their paper could soon inform further neuroscience studies focusing on early brain development, while also potentially informing the creation of new artificial intelligence (AI) models that emulate the dynamics they observed.

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