Hearing test in a newborn baby. Image credit: Solen Feyissa (CC BY 4.0)
Our brains have an amazing ability to adapt to changes in our environment or bodies, sometimes even ‘rewiring’ themselves as a result. This ‘rewiring’ is called plasticity, and it is especially important when one or more of our senses – such as sight or hearing – do not work.
In people born with deafness, a condition termed ‘congenital deafness’, the part of the brain that normally processes sounds (called the auditory cortex) reorganizes itself to process information from other senses, especially vision. This cross-modal plasticity lets the auditory cortex compensate for the missing sense of hearing by forming new connections to different brain areas. However, it is still unclear if this reorganization of the auditory cortex differs across individuals born with deafness.
Amaral, Wang et al. wanted to investigate if different people’s brains have distinct ways of adapting to deafness. Specifically, they tested if congenital deafness influenced the way the auditory cortex in different people was connected to other parts of the brain. They also tested if exposure to sign language early in life affected those connections.
To do this, Amaral, Wang et al. used a brain imaging technique called fMRI to scan the brains of both congenitally deaf participants and people with healthy hearing. This showed that most of the hearing participants had similar connections between the auditory cortex and other parts of the brain.
In contrast, the connectivity of the auditory cortex – particularly to brain areas that process language – was much more diverse across deaf individuals. This diversity was even present in ‘native signer’ deaf participants exposed to sign language very early in life. However, comparing the native signers to deaf individuals who learned sign language much later showed that the native signers had much more consistent connections between the auditory cortex and two specific areas associated with sign language comprehension. These results indicate that both deafness and early exposure to language can shape individual differences in brain plasticity.
These findings shed new light on how sensory loss and language exposure can shape people’s brains in different ways. In the future, Amaral, Wang et al. hope that the knowledge gained will benefit people with deafness or hearing loss, for example, by helping develop better tools to restore hearing or contributing to more personalised approaches to language and education in general.
