Why do congenitally blind people show activity in brain areas for visual processing
Abstract: The study reveals structural changes in the connectivity of the thalamus with other areas of the brain in people with congenital blindness, providing evidence of brain plasticity. The areas of the thalamus that connect to the occipital lobe in the blind are weaker and smaller, giving way to connections in the temporal cortex that are strengthened.
Recently published in a scientific journal Mapping 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 carried out by the Institute for Research and Education D’Or (IDOR), the Federal University of Rio de Janeiro (UFRJ) and the Center for Specialized Ophthalmology in Brazil.
Decades ago, scientific studies reported the unusual discovery that people born blind can activate the brain’s vision-processing area, 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, which is the brain’s ability to reorganize its connections to cope with adversity. This process may involve a number of structural modifications, such as the development of new neural pathways or the reorganization of existing connections.
“Soon after we are born, we are exposed to stimuli that are captured by our senses, and which are fundamental for determining the electrical circuit of the brain. It is also a time when our brain is undergoing a major transformation.
“Technically, we might think that the occipital cortex would be dysfunctional in people who were born blind, but we know that’s not the case. It is activated. What we lacked to understand was the structural process behind it,” explains Dr. Fernanda Tovar-Moll, corresponding author of the current study and president of IDOR.
In the research, magnetic resonance techniques were used to analyze the structural connectivity in the human brain and to investigate the possibility of alternative neural connections. Neural images of 10 people with congenital blindness and Braille readers were compared with a control group of 10 people with intact vision.
After detailed analysis, the scientists observed structural changes in connectivity in the thalamus, a structure located in the diencephalon, the central part of the brain that receives, processes and distributes information captured by the main human senses – such as sight, 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 remote areas of the brain represent this communication, we suspected that the phenomenon originates in the thalamus, since it is the brain structure responsible for connecting several cortical regions, and this could be an area that with small changes in the axon circuit [part of the neuron responsible for conducting electrical impulses] could connect cortices that were far from each other”, comments the neuroscientist.
The research also noted that the area of the thalamus dedicated to connecting with the occipital cortex (vision) was smaller and weaker in blind individuals, giving way to connections with the temporal cortex (hearing), which were shown to be strengthened compared to those observed in unimpaired individuals. sight. This means that in addition to being activated, the visual cortex is also attacked by connections that refine other senses, such as hearing and touch.
It was the first time that a study in humans described alternative mapping in the connection of the thalamus with the occipital and temporal cortex, and these plastic reorganizations may be a mechanism that can explain how non-visual stimuli reach and activate the visual cortex in congenitally blind individuals.
“Neuroimaging studies allow us to navigate the structure of the brain and better understand the diversity of brain plasticity, which can also pave the way for discoveries such as new vision rehabilitation initiatives,” adds Dr. Tovar-Moll, informing that her research group is still involved in other research. with congenitally blind people in which they investigate, in addition to the structure, also the functional adaptations of brain plasticity in this population.
About this visual neuroscience research news
Original research: Open access.
“Reorganization of thalamocortical connections in congenitally blind people” Fernanda Tovar-Moll et al. Mapping the human brain
Reorganization of thalamocortical connections in congenitally blind people
Cross-modal plasticity in blind individuals has been reported over the past decades showing that non-visual information is conveyed and processed by “visual” brain structures. However, despite multiple efforts, the structural basis of cross-modal plasticity in congenitally blind individuals remains unclear.
We mapped thalamocortical connectivity and assessed white matter integrity in 10 congenitally blind individuals and 10 sighted control individuals.
We hypothesized that an aberrant thalamocortical pattern of connectivity occurs in the absence of visual stimuli from birth as a potential mechanism of cross-modal plasticity. In addition to the disturbed microstructure of the bundles of visual white matter, we observed structural changes in the connection between the thalamus and the occipital and temporal cortex.
Specifically, the thalamic territory dedicated to connections with the occipital cortex was smaller and showed weaker connectivity in congenitally blind individuals, while those connecting to the temporal cortex showed a larger 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 is shown, shedding light on possible mechanisms of crossmodal plasticity in humans.
These findings may help to understand the functional adaptations commonly observed in congenitally blind individuals.