Speech processing activates visual cortex in congenitally blind humans

Abstract

Neurophysiological recordings and neuroimaging data in blind and deaf animals and humans suggest that perceptual functions may be organized differently after sensory deprivation. It has been argued that neural plasticity contributes to compensatory performance in blind humans, such as faster speech processing. The present study employed functional magnetic resonance imaging (fMRI) to map language-related brain activity in congenitally blind adults. Participants listened to sentences, with either an easy or a more difficult syntactic structure, which were either semantically meaningful or meaningless. Results show that blind adults not only activate classical left-hemispheric perisylvian language areas during speech comprehension, as did a group of sighted adults, but that they additionally display an activation in the homologueous right-hemispheric structures and in extrastriate and striate cortex. Both the perisylvian and occipital activity varied as a function of syntactic difficulty and semantic content. The results demonstrate that the cerebral organization of complex cognitive systems such as the language system is significantly shaped by the input available.

Language processing in the occipital cortex of congenitally blind adults

“…Based on the present findings, we conclude that the left-lateralized occipital activity during verbal tasks reflects language processing (25,35,41). However, prior studies have shown that regions of the occipital cortex in blind individuals also contribute to multiple nonverbal tasks, such as tactile discrimination and sound localization (42,43).…”

“…However, almost all prior studies of language in congenitally blind individuals have used single words. Suggestive evidence comes from one study that found an increase in occipital activity with increased grammatical complexity (35), but in that study the grammatically complex condition was also more difficult and led to greater activity in all examined brain regions and all groups. We therefore sought to establish whether the occipital areas of congenitally blind individuals are specifically sensitive to combinatorial linguistic processing.…”

Habilidade de localização e lateralização sonora em deficientes visuais

“…Resultados semelhantes foram descritos por outros autores (8,(11)(12)(13)(14)(15) . Na atenção direcionada para a audição periférica espacial, a localização de sons mostra-se significativamente melhor nos indivíduos cegos do que nos videntes, bem como nas tarefas de localização sonora monoaural (11) .…”

“…Imagens de ressonância magnética funcional de indiví-duos com privação sensorial demonstram que a plasticidade neuronal contribui para um melhor desempenho de indivíduos deficientes visuais, em atividades como processamento de fala (13) . A plasticidade neural é a "capacidade que o sistema nervoso central possui em modificar algumas das suas propriedades morfológicas e funcionais, em resposta às alterações do ambiente" (18) .…”

“…Sabemos que habilidades auditivas como o processamento temporal são de extrema importância para a identificação de elementos fonéticos, contribuindo assim para a percepção de fala (22)(23) . Podemos, então, afirmar que a percepção de fala de deficientes visuais é melhor do que a de indivíduos videntes, pelo fato de processarem melhor e com maior efetividade as propriedades físicas dos sons da fala (freqüência, intensidade e duração) (13)(14)(15) . O que poderia ter proporcionado essa melhor percepção auditiva?…”