Summary: The study reveals structural changes in the connectivity of the thalamus to other brain areas in people with congenital blindness, providing evidence for brain plasticity. Areas of the thalamus that connect to the occipital lobe in blind people are weaker and smaller, leaving room for connections in the temporal cortex that are strengthened.
Source: IDOR
Recently published in the scientific journal Mapping of the human braina Brazilian study has identified for the first time 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 Specialized Ophthalmology Center of Brazil.
A few decades ago, scientific studies reported the curious discovery that people born blind could activate the vision-processing region of the brain, the occipital cortex, when engaging in non-visual activity, such as reading in braille (a tactile language system) .
These studies were further evidence of so-called brain plasticity, which is the ability of the brain to rearrange its connections to deal with adversity. This process can involve a series of structural changes, such as developing new neural pathways or rearranging existing connections.
“Shortly after we are born, we are exposed to stimuli picked up by our senses, which are fundamental in determining the circuits of the brain. It is also a period when our brain is in great transformation.
“Technically, we would think that the occipital cortex would be functionless in people born blind, but we know that is not the case. It is activated. What we lacked to understand was the underlying structural process,” says Dr. Fernanda Tovar-Moll, corresponding author of the current study and chair of IDOR.
In research, magnetic resonance imaging techniques have been used to analyze structural connectivity in the human brain and to investigate the possibility of alternative neural connections. The neural images of 10 people with congenital blindness and Braille readers were compared to a control group of 10 people with intact vision.
After a 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 different regions of the brain.
“Plasticity has been the focus of our group’s research for many years, and in this case of cross-modal plasticity in congenitally blind people, in which distant areas of the brain exhibit this communication, we suspected the phenomenon might have originated the thalamus, since it is the brain structure responsible for connecting several cortical regions, and it could be an area that, with little change in the axonal circuits [part of the neuron responsible for conducting electrical impulses] would be able to connect cortices far apart from each other”, comments the neuroscientist.
Research also observed that the area of the thalamus dedicated to connection with the occipital cortex (vision) was smaller and weaker in blind people, leaving room for connections with the temporal cortex (hearing), which were found to be reinforced compared to those observed in people without visual impairment. This means that in addition to being activated, the visual cortex is also invaded by connections that sharpen other senses, such as hearing and touch.
This was the first time that a study described in humans an alternative mapping in the connectivity of the thalamus with the occipital and temporal cortices, and these plastic reorganizations could be a mechanism capable of explaining how non-visual stimuli reach and activate the visual cortex in congenitally blind people.
“Neuroimaging studies allow us to navigate brain structure and better understand the diversity of brain plasticity, which may also pave the way for discoveries such as new vision rehabilitation initiatives,” adds Dr. Tovar- Moll, informing that his research group is still involved in other studies with congenitally blind people in which they study, 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
Picture: Image is in public domain
Original research: Open access.
“Reorganization of thalamocortical connections in congenitally blind humans” by Fernanda Tovar-Moll et al. Mapping of the human brain
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Summary
Reorganization of thalamocortical connections in congenitally blind humans
Cross-modal plasticity in blind people has been reported over the past decades, showing that non-visual information is carried and processed by “visual” brain structures. However, despite multiple efforts, the structural underpinnings of crossmodal plasticity in congenitally blind people remain unclear.
We mapped thalamocortical connectivity and assessed white matter integrity in 10 congenitally blind individuals and 10 sighted controls.
We hypothesized an aberrant thalamocortical connectivity pattern that occurs in the absence of visual stimuli from birth as a potential mechanism for crossmodal plasticity. In addition to altered microstructure of visual white matter tracts, we observed changes in structural connectivity between the thalamus and the occipital and temporal cortices.
Specifically, the thalamic territory dedicated to connections with the occipital cortex was smaller and showed lower connectivity in congenitally blind people, while those connecting to the temporal cortex showed 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, remapping of structural thalamocortical connections involving both unimodal and multimodal thalamic nuclei has been demonstrated, shedding light on possible mechanisms of crossmodal plasticity in humans.
The present results may help to understand the functional adaptations commonly observed in people who are congenitally blind.
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