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

Overview: Study reveals structural changes of connectivity in the thalamus to other brain regions in people with congenital blindness, providing evidence for brain plasticity. The parts 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 to be strengthened.

Source: DRY

Recently published in the scientific journal Mapping human brainsa Brazilian study has for the first time identified the reorganization of anatomical structures in the brains of people with congenital blindness.

The research was conducted by the D’Or Institute for Research and Education (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 born blind could activate the face-processing area of ​​the brain, the occipital cortex, when engaged in a non-visual activity, such as reading Braille (a tactile language system). .

These studies were further evidence of so-called brain plasticity, the brain’s ability to reorganize its connections to cope with adversity. This process can involve a series of structural changes, such as developing new neural pathways or reorganizing existing connections.

“Shortly after we are born, we are exposed to stimuli received by our senses, which are fundamental in determining the circuitry of the brain. It is also a time when our brain is in great transformation.

“Technically, we might think that the occipital cortex would be functionless in people born blind, but we know that’s not the case. It’s activated. What we didn’t understand was the structural process behind it,” explains Dr. Fernanda Tovar-Moll, corresponding author of the current study and president of IDOR.

The study used magnetic resonance imaging techniques to analyze structural connectivity in the human brain and to explore 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 in the diencephalon, the central part of the brain that receives, processes and distributes information received by the major human senses – such as vision, hearing and touch – to the different brain regions.

“Plasticity has been the research focus of our group for many years, and in this case of cross-modal plasticity in congenital blind people, where distant parts of the brain present this communication, we suspected that the phenomenon would originate in the thalamus, since it is the brain structure responsible for connecting different cortical areas, and it could be an area that has little change in the axonal circuitry [part of the neuron responsible for conducting electrical impulses] could connect cortices that are far apart,” notes the neuroscientist.

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

The study also found that the area of ​​the thalamus destined for connection to the occipital cortex (sight) was smaller and weaker in blind individuals, making room for connections to the temporal cortex (hearing), which was shown to stronger than those of the thalamus. observed in individuals without visual impairment. This means that the visual cortex is not only activated, but also invaded by connections that refine other senses, such as hearing and touch.

It was the first time that a human study described an alternative mapping in the connectivity of the thalamus to the occipital and temporal cortex, and these plastic reorganizations may be a mechanism that may explain how non-visual stimuli reach and activate the visual cortex in congenital blind people.

“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, who shares that her research group is still involved in other studies with congenital blind people exploring the functional adaptations of brain plasticity in this population in addition to structure.

About this visual neuroscience research news

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

Original research: Open access.
“Reorganization of thalamocortical connections in congenitally blind humans” by Fernanda Tovar-Moll et al. Mapping human brains

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Reorganization of thalamocortical connections in congenitally blind humans

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

We mapped thalamocortical connectivity and assessed white matter integrity of 10 congenital blind individuals and 10 sighted controls.

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

In particular, the thalamic territory devoted to connections to the occipital cortex was smaller and showed weaker connectivity in congenitally blind individuals, while those connecting to the temporal cortex showed greater volume and connectivity. The abnormal pattern of thalamocortical connectivity involved the lateral and medial geniculate nuclei and the pulvinar nucleus.

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

The current findings may aid in understanding the functional adaptations commonly observed in congenitally blind individuals.

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