A brain that develops in the deprivation of one sense reorganises itself in surprising ways, revealing remarkable neuroplasticity. Researchers studied the brain activity of young congenitally deaf and young hearing individuals during a visual task and concluded that the brain can reorganise sensory systems not only through increased activation but also through selective deactivation.

Neuroplasticity allows the human brain to reorganise throughout life, especially under conditions of sensory deprivation. Studies on congenital blindness and deafness show that areas deprived of stimulation can be recruited to process information from other modalities, a phenomenon known as cross‑modal plasticity. In both animal models and humans, it has been shown that the visual cortex deprived of vision can support auditory, tactile, or linguistic tasks, and that the auditory cortex deprived of sound can respond to visual stimuli.

In congenital deafness, previous studies had already demonstrated that vision can recruit areas typically dedicated to audition. In other words, the reorganised auditory cortex responds to visual stimuli such as motion, rhythm, or location within the visual field, and this reorganisation is associated with behavioural advantages in visual tasks. Despite these findings, how the reorganised auditory cortex represents low‑level visual spatial features in humans remained poorly understood.

To address this question, Alessio Fracasso, supported by the Bial Foundation, and collaborators examined the brains of young congenitally deaf and hearing individuals as they viewed simple visual patterns. By presenting classical stimuli that systematically sweep across different portions of the visual field, the researchers used functional magnetic resonance imaging to analyse how several brain regions responded to this stimulation.

In hearing participants, the results followed the expected pattern: the visual cortex activated according to stimulus location, while the auditory cortex showed no relevant modulation. In deaf participants, however, an unexpected phenomenon emerged. Instead of showing increased activity, the auditory cortex displayed systematic deactivation of the neural signal when visual stimuli appeared. The authors demonstrated that these deactivations were stimulus‑dependent and not mere noise, suggesting organised visual representation within auditory regions deprived of sound input.

More detailed exploratory analyses showed that these deactivations in the auditory cortex follow an organised pattern: they respond primarily to stimuli on the opposite side of the visual field, are more concentrated in central vision, and cover relatively large areas of space, indicating that this region is indeed representing where visual stimuli are located.

These findings were published in the article The neural organization of visual information in the auditory cortex of the congenitally deaf, in the scientific journal Human Brain Mapping, co-authored by an international team of researchers affiliated with the University of Coimbra (PT), University of Glasgow (UK), University of Padua (IT), and Peking University (CN).

According to Alessio Fracasso, this study “opens a new perspective on brain plasticity, showing that the brain does not simply substitute one sense for another through increased activation, it can also do so through selective deactivation, perhaps as a way of filtering irrelevant information or optimising visual attention”. Incorporating these deactivations into existing models and theories “may offer a more comprehensive understanding of sensory reorganisation in systems deprived of stimulation, expanding our knowledge of the mechanisms and functionality of cross‑modal plasticity”, the researcher explains.

Learn more about the project “203/2020 - Dynamic eye-movement encoding in human cortex using ultra-high field fMRI (7Tesla)” here.