Why people with congenital blindness show activity in the visual processing areas of the brain

Summary: Study reveals structural connectivity changes in the thalamus to other brain areas in people with congenital blindness, providing evidence of brain plasticity. The areas of the thalamus that connect to the occipital lobe in people with blindness are weaker and smaller, making room for connections in the temporal cortex that are strengthened.

Source: IDOR

Recently published in the scientific journal Mapping the Human Braina Brazilian study identified for the first time the reorganization of anatomical structures in the brain of people with congenital blindness.

The survey was carried out by the D’Or Institute for Research and Teaching (IDOR), the Federal University of Rio de Janeiro (UFRJ) and the Center for Specialized Ophthalmology, Brazil.

A few decades ago, scientific studies reported the curious discovery that people who were blind from birth could activate the region of the brain that processes vision, the occipital cortex, when engaging in a non-visual activity such as reading Braille (a language system). tactile). .

These studies were further evidence of the so-called brain plasticity, which is the brain’s ability to reorganize its connections to face adversity. This process can involve a series of structural modifications, such as the development of new neural pathways or the reorganization of existing connections.

“As soon as we are born, we are exposed to stimuli captured by our senses, fundamental to determine the circuits of the brain. It is also a time when our brain is undergoing a major transformation.

“Technically, you might think that the occipital cortex wouldn’t work in people who were born blind, but we know that’s not the case. Is enabled. What was not understood was the structural process behind it”, explains Dr. Fernanda Tovar-Moll, corresponding author of the current study and chair of IDOR.

In the research, magnetic resonance imaging techniques were used to analyze structural connectivity in the human brain and investigate the possibility of alternative neural connections. The neural images of 10 individuals with congenital blindness and Braille readers were compared to a control group of 10 individuals with intact vision.

After detailed analysis, the scientists observed structural changes in connectivity in the thalamus, a structure located in the diencephalon, the central region of the brain that receives, processes and distributes information captured by the main human senses – such as vision, hearing and touch – to the different regions of the brain.

“Plasticity has been the research focus of our group for many years and, in this case of cross-modal plasticity in congenitally blind people, in which distant areas of the brain present this communication, we suspect that the phenomenon would be originating in the thalamus, as it is the brain structure responsible for connecting various cortical regions, which may be an area with little change in the axonal circuit [part of the neuron responsible for conducting electrical impulses] it would be able to connect cortices that are distant from each other”, comments the neuroscientist.

This shows a model of a head and brain
In the research, magnetic resonance imaging techniques were used to analyze structural connectivity in the human brain and investigate the possibility of alternative neural connections. The image is in the public domain

The research also observed that the area of ​​the thalamus dedicated to the connection with the occipital cortex (vision) was smaller and weaker in the blind, giving way to connections with the temporal cortex (hearing), which were shown to be strengthened when compared to those observed in individuals without Visual impairment. This means that, in addition to being activated, the visual cortex is also invaded by connections that refine other senses, such as hearing and touch.

It was the first time that a study in humans described an alternative mapping in the connectivity of the thalamus with the occipital and temporal cortices, and these plastic reorganizations may be a mechanism capable of explaining how non-visual stimuli reach and activate the visual cortex in people blind from birth. .

“Neuroimaging studies allow us to navigate the structure of the brain and better understand the diversity of brain plasticity, which may also pave the way for discoveries such as new visual rehabilitation initiatives,” adds Dr. Tovar-Moll, informing that his research group is still involved in other studies with congenitally blind people in which they investigate, in addition to the structure, the functional adaptations of brain plasticity in this population.

About this visual neuroscience research news

Author: Leandro Tavares
Source: IDOR
Contact: Leandro Tavares – IDOR
Image: The image is in the public domain

Original search: Free access.
“Reorganization of thalamo-cortical connections in congenitally blind humans” by Fernanda Tovar-Moll et al. Mapping the Human Brain

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This shows the outline of two heads

Summary

Reorganization of thalamocortical connections in congenitally blind humans

Cross-modal plasticity in blind individuals has been reported in recent decades, showing that non-visual information is transported and processed by “visual” brain structures. However, despite various efforts, the structural underpinnings of cross-modal plasticity in congenitally blind individuals remain unclear.

We mapped thalamocortical connectivity and assessed white matter integrity in 10 congenitally blind subjects and 10 sighted controls.

We hypothesized an aberrant pattern of thalamocortical connectivity occurring in the absence of visual stimuli from birth as a potential mechanism of cross-modal plasticity. In addition to the impaired microstructure of the visual white matter bundles, we observed changes in the structural connectivity between the thalamus and the occipital and temporal cortices.

Specifically, the thalamic territory devoted to connections with the occipital cortex was smaller and exhibited weaker connectivity in congenitally blind individuals, while those connecting with the temporal cortex had greater volume and increased connectivity. The abnormal pattern of thalamocortical connectivity included the lateral and medial geniculate nuclei and the pulvinar nucleus.

For the first time in humans, a remapping of structural thalamocortical connections involving unimodal and multimodal thalamic nuclei has been demonstrated, shedding light on possible mechanisms of cross-modal plasticity in humans.

Our findings may help to understand the functional adaptations commonly observed in congenitally blind individuals.

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