Study explains how the brain adapts to lack of vision

posted on 01/21/2023 06:00

Worldwide, vision impairment affects at least 2.2 billion people, and a significant proportion of these people suffer from congenital blindness, a process that occurs before or during birth. The impact of this condition on sensory and neurological systems has been the focus of studies in recent years, with researchers trying to understand how the brain articulates from the absence of visual stimuli. Now, a new Brazilian study has uncovered the phenomenon of brain plasticity in people born without sight, demonstrating how non-visual stimuli reach the part of the brain responsible for the absent sense and help the organ adapt.

Brain plasticity is defined by the brain’s ability to rearrange and rearrange the connections between neurons, which are the cells responsible for generating and transmitting nerve impulses, explains Pedro Sudbrack, doctor at the University of Brasilia (UnB) and with a residency in neurology. of the Federal University of Rio de Janeiro (UFRJ). “This reorganization normally occurs throughout the life of the individual, being most intense in the fetal period and in early childhood,” he says. ‘Exposure to specific types of stimuli in the environment is essential for the development of brain circuits responsible for processing and perceiving that type of stimulus,’ he adds.

In research published in the scientific journal Human Brain Mapping, the team used magnetic resonance imaging to analyze the possibility of alternate brain connections in people born blind. The neural images of 10 individuals with congenital blindness and Braille readers were compared with those of a control group, made up of 10 people without visual impairment. Scientists from the D’Or Institute for Research and Teaching (Idor), the Federal University of Rio de Janeiro (UFRJ) and the Center for Specialized Ophthalmology, where they found structural changes in the connectivity in the thalamus, a region that acts in the relay information ai major sensory systems.

Fernanda Tovar-Moll, coordinator of the study and president of Idor, explains that plasticity has been at the center of the research of the group for many years and that the current study has allowed to analyze its relationship with congenital blindness. “In this case of cross-plasticity in congenitally blind people, where distant areas of the brain exhibit this communication, we suspect that the phenomenon would originate in the thalamus, as it is the brain structure that connects different distant cortical regions together,” he says, in a note.

The team observed that the area of ​​the thalamus dedicated to connections with the occipital cortex, responsible for vision, was smaller and weaker in blind subjects, giving way to connections with the temporal cortex (hearing), which appeared to be more stronger than they could not see in individuals without disabilities. “Connections between neurons that fire more frequently tend to get stronger, while those that are underused tend to get weaker,” comments Sudbrack. “This could suggest that vision-related regions of the thalamus are flooded with connections that sharpen other senses, such as hearing.”

Functional

Natanael de Abreu Sousa, strabismus and neuro-ophthalmology specialist at the Hospital Oftalmológico de Brasília (HOB), explains that the thalamus is of great functional importance, since it is a condensation of neurons located in the center of the brain. “The optic nerve fibers of each eye connect to the posterolateral part of the thalamus. Not only the fibers of vision, but all other sense organs, with fibers carrying information about heat, temperature, touch, the sense of each part of the body, what we call proprioception,” he says. “As far as hearing is concerned, there is an auditory nerve that carries information to the thalamus and, from there, to the cortex, allowing us to interpret what we hear in the form of sounds, music and words.”

Previous research had shown that people with congenital blindness are able to activate the region of the brain responsible for vision through non-visual stimuli, such as reading Braille. But it was the first time that a study had described alternative connectivity of the thalamus with cortices related to vision and hearing. “This demonstrates the importance of other sensory entry points to compensate for what is missing,” comments Natanael de Abreu. “Everything arrives at the thalamus, where it is processed, stimulating different cortices. But it could also cross-stimulate the occiput, which would not remain inert due to the absolute lack of vision in a child with congenital blindness”.

*Intern under the supervision of Carmen Souza

Three questions for…

Tiago Ribeiro, pediatric ophthalmologist at the Visão Hospital de Olhos, in Brasilia

What is congenital blindness?

Congenital blindness is a term we use for the various diseases that cause a child to be born blind. And there are different diseases: there are retinal dystrophies, there are changes in the shape of the eye, changes caused by infectious diseases, changes caused by tumors…

How is it detected?

If it is a very large structural change, it will already be seen in the eye exam, especially when examining the enlarged eye. And some structural changes in the retina or the shape of the eyeball can be felt in the morphological ultrasound. Inside the mother’s belly it is already possible to evaluate the eyes and, depending on the technique with which the ultrasound is performed, structures inside the eyes can be evaluated, such as the baby’s lens. There are changes that cannot be seen on this gestational ultrasound. Now, if it’s really big structural changes, you can be suspicious.

What are the forms of prevention?

Congenital blindness is a term used for several diseases, some of which, such as infectious and parasitic diseases, can be prevented. The pregnant woman must be careful about what she eats, avoid foods that are undercooked, raw or whose origin she does not know or which have not been adequately cleaned. Do not abuse alcohol and drugs, because they can also be related to morphological alterations of the eye and make the prenatal segments. Some diseases can be detected during this follow-up and treated before they affect the fetus.