Summary: A Brazilian neuroimaging study reports structural changes in thalamic connections in people with congenital blindness, providing new evidence of brain plasticity. The regions of the thalamus that normally connect with the occipital (visual) cortex are reduced in size and connectivity in those born blind, while thalamic connections to the temporal cortex are strengthened, suggesting an anatomical basis for cross-modal processing of non-visual information.
Source: IDOR
Correction: The original post was edited to include the writer and contact information in the source section.
Researchers from the D’Or Institute of Research and Education (IDOR), the Federal University of Rio de Janeiro (UFRJ), and the Center for Specialized Ophthalmology in Brazil have published new findings in the journal Human Brain Mapping identifying anatomical reorganization in the brains of people born blind.
Past studies showed that people with congenital blindness can recruit the occipital cortex—the region typically dedicated to visual processing—during non-visual tasks such as Braille reading. Those functional observations supported the concept of brain plasticity: the brain’s ability to rewire itself following atypical sensory experience. What has been less clear until now is the structural pathway that allows non-visual information to reach and engage traditionally visual brain areas.
“Shortly after birth, sensory inputs help shape the brain’s circuitry during a highly plastic developmental window,” explains Dr. Fernanda Tovar-Moll, corresponding author and president of IDOR. “While the occipital cortex might appear functionless without vision, it is in fact active. We sought to discover the structural changes that underpin that activity.”
The team applied magnetic resonance imaging (MRI) techniques to map structural connectivity and white matter integrity. They compared neural images from 10 congenitally blind, Braille-reading participants with those from 10 sighted control subjects to investigate whether alternative thalamocortical pathways could explain cross-modal activation of visual regions.
Their analyses revealed specific structural alterations in the thalamus, a central brain structure responsible for relaying and distributing sensory information to cortical regions. In congenitally blind individuals the thalamic territory that normally connects with the occipital cortex was smaller and showed weaker connectivity. In contrast, the zones of the thalamus connecting with the temporal cortex—associated with auditory processing—were larger and exhibited stronger connections.
This pattern suggests that in the absence of visual input from birth, thalamic circuits can be reorganized so that non-visual signals gain more direct anatomical access to regions typically devoted to vision. The study identified involvement of multiple thalamic nuclei, including the lateral and medial geniculate nuclei and the pulvinar, indicating that both unimodal and multimodal thalamic areas participate in this remapping.
“Our group has long been interested in plasticity, and in this form of cross-modal plasticity we suspected the thalamus might be a key node: a small shift in axonal circuitry there could enable connections between distant cortical areas,” Dr. Tovar-Moll adds. The findings provide the first human evidence of a remapped thalamocortical connectivity profile that could account for how auditory and tactile information reach and activate the visual cortex in people born blind.
Beyond explaining a fundamental neurobiological mechanism, these results have practical implications: improved understanding of structural plasticity may inform novel approaches to sensory rehabilitation and adaptive technologies. Dr. Tovar-Moll notes her group continues to study both structural and functional adaptations in congenitally blind populations to explore how these brain changes relate to behaviour and perception.
About this visual neuroscience research news
Author: Written by Maria Eduarda Ledo de Abreu
Source: IDOR
Contact: [email protected]
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., Human Brain Mapping. DOI: 10.1002/hbm.26192
Abstract
Reorganization of thalamocortical connections in congenitally blind humans
Cross-modal plasticity in people born blind has been documented for decades: non-visual information is processed by brain regions typically considered “visual.” However, the detailed structural basis for this cross-modal processing has remained unclear. This study mapped thalamocortical connectivity and examined white matter integrity in 10 congenitally blind individuals and 10 sighted controls.
The authors hypothesized that an altered thalamocortical connectivity pattern, emerging in the absence of visual input from birth, could explain cross-modal activation of the occipital cortex. Consistent with that hypothesis, they found impaired microstructure of visual white matter tracts and observed a shift in thalamic connections: territories linking the thalamus to the occipital cortex were reduced in volume and connectivity in the blind group, while connections to the temporal cortex increased in volume and strength.
This abnormal thalamocortical organization involved the lateral and medial geniculate nuclei as well as the pulvinar. For the first time in humans, these results demonstrate a remapping of structural thalamocortical connections that includes both unimodal and multimodal thalamic nuclei, offering a plausible anatomical mechanism for cross-modal plasticity and helping to explain the functional adaptations observed in congenitally blind individuals.