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Is the deaf cat a better observer?
Researchers, led by luminaries such as Lomber et al. (2010) and Meredith et al. (2011), have delved deep into the brain plasticity of deaf cats’ auditory cortex. Contrary to expectations, these cats exhibited not only normal behaviour but also enhanced visual skills compared to their hearing counterparts, as shown in tasks involving far periphery and motion detection. These observations were explained by the fact that the loss of the auditory sensory modality induced cortical reorganization (the brain’s ability to redistribute neural resources in the face of sensory deprivation) that led to enhanced visual performance. Further insights into the function of auditory areas showed that the auditory-to-visual plasticity was specific to higher-order auditory areas (i.e., the ones involved in complex processing) whereas it was not reflected in the activity of the primary auditory cortex. Furthermore, this sensory adaptation is not permanent as highlighted by recent studies comparing the auditory neural responses to visual stimuli before and after restoring hearing (with cochlear implants) in deaf cats. The restoration of auditory function resulted in a reduction in visual responses, suggesting a return to basal activity. This breakthrough sheds light on the nuanced mechanisms of cross-modal sensory adaptation at various stages of auditory processing across the functional hierarchy.
The Puzzle of Cortical Reorganisation
Central to this conundrum is the phenomenon of cortical reorganisation – the brain’s ability to redistribute neural resources in the face of sensory deprivation. In deaf individuals, the auditory cortex may repurpose itself to accommodate visual stimuli, a process known as cross-modal plasticity. Yet, with the introduction of cochlear implants for individuals with severe hearing loss the auditory cortex seamlessly transitions back to processing auditory signals, posing a fascinating paradox.
Questioning the brain’s functional representation
The measure of how the brain reorganises itself depends on how it responds to new sensory experiences, adapts its processing abilities, and shows coherent behaviour. However, traditional studies lack solid proof to evaluate this phenomenon of brain plasticity. Although widely believed, the idea of reorganization is doubted because the functional maps of the brain created by researchers might oversimplify how the brain works. As emphasised by Penfield, the depiction of various body parts in the brain is widely spread out, with unclear boundaries at most, suggesting that the organisational structure imposed by these artificial maps may not entirely reflect the actual functional arrangement.
Credits
Author: Vivek Sharma Buddy: Kim Beneyton Editor: Swantje Neil Translation: Judith Scholing Editor translation: Lucas Geelen