Summary: A brain developing without one sense reorganizes in surprising ways, but new research reveals that this plasticity isn’t always about “turning on” new areas. The study found that in congenitally deaf individuals, the auditory cortex represents visual information through selective deactivation.
Rather than firing more neurons, the brain systematically “dims” the auditory signal in response to specific visual locations, suggesting that inhibitory signals are a key, and previously overlooked, mechanism for sensory compensation.
Key Facts
- Organized Deactivation: In congenitally deaf individuals, the auditory cortex doesn’t just “switch on” to help with vision; it shows systematic selective deactivation of neural signals that precisely map to the location of visual stimuli.
- Spatial Mapping: These deactivations follow a structured pattern, primarily responding to stimuli in the opposite visual field and focusing on central vision, proving the auditory cortex is actively representing visual space.
- A New Rule for Plasticity: This discovery redefines neuroplasticity by showing the brain can repurpose “silent” areas through inhibitory signals, likely to optimize visual attention and filter out sensory noise.
- Scientific Impact: The study suggests that models of brain reorganization must now account for deactivation as a primary functional mechanism for sensory compensation.
Source: Bial Foundation
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.
Key Questions Answered:
A: It’s likely an efficiency move. By deactivating specific parts of the auditory cortex, the brain may be filtering out “neural noise” or irrelevant information, allowing the individual to focus more intensely on visual spatial cues. Think of it as dimming the house lights to see the stage more clearly.
A: No. In the hearing control group, visual stimuli activated the visual cortex as expected, but the auditory cortex showed no relevant modulation. This specific “remapping” via deactivation appears to be a unique adaptation to congenital deafness.
A: This is a hallmark of organized mapping. If a light flashes on your left, the right side of the brain’s auditory cortex deactivates. This structured “contralateral” response proves the auditory cortex has been fully recruited into a functional visual map.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this auditory neuroscience research news
Author: Sandra Pinto
Source: BIAL Foundation
Contact: Sandra Pinto – BIAL Foundation
Image: The image is credited to Neuroscience News
Original Research: Open access.
“The Neural Organization of Visual Information in the Auditory Cortex of the Congenitally Deaf” by Zohar Tal, Joana Sayal, Fang Fang, Yanchao Bi, Jorge Almeida, Alessio Fracasso. Human Brain Mapping
DOI:10.1002/hbm.70444
Abstract
The Neural Organization of Visual Information in the Auditory Cortex of the Congenitally Deaf
Neuroplasticity is the brain’s ability to reorganize its structural and functional architecture throughout life. In congenital deafness, the sensory-deprived auditory cortex can be recruited to represent sensory information belonging to other modalities, a process known as cross-modal plasticity.
Previous studies have indicated that the auditory cortex of congenitally deaf, but not of hearing individuals, is recruited during visual tasks. However, it remains unclear whether and to what extent these cross-modal responses represent low-level visual spatial information or map the visual field.
Here, we addressed this question using two complementary fMRI experiments focusing on cross-modal processing in the auditory cortex of both deaf and hearing individuals during passive viewing of conventional visual stimuli.
The first experiment, at the group level, revealed that, unlike in hearing individuals, the auditory cortex of deaf individuals predominantly exhibited negative BOLD signals in early and associative auditory areas—a surprising finding given the prevailing focus on activations in prior work.
These negative BOLD signals—commonly interpreted as deactivation responses—suggest that visual information may be represented via cross-modal deactivation mechanisms.
We complement the investigation with an exploratory follow-up analysis using pRF modeling in a subset of participants.
Together, our findings indicated that, in congenitally deaf individuals, cross-modal visual processing in the auditory cortex may be mediated by deactivation signals, offering new insights into the neural basis of sensory reorganization.
