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Centre for Neuroscience in Education


A new publication from the project funded by the Fondation Botnar was published in the Frontiers in Human Neuroscience Journal, in September 2023. 

Neural responses to natural and enhanced speech edges in children with and without dyslexia

Dyslexia is a developmental language disorder affecting reading and spelling. While traditionally viewed as a disorder of written language processing, recent investigations have revealed a possible link between dyslexia and atypical synchronization of speech rhythms and neural oscillations in the brain during oral language processing. Our previous research (Goswami, 2011; Mandke et al., 2022) has suggested that these challenges in spoken language processing manifest before children embark on their reading journeys. We think the answer to why dyslexia develops lies in the disrupted relations between neural oscillations (i.e., brain rhythms) and the acoustic rhythms of speech. Our brains, akin to musical instruments, exhibit intricate rhythms at different speeds, such as delta (0-4Hz), theta (4-8Hz), and alpha (8-13Hz). These rhythms serve as the physiological basis for processing and comprehending speech information. Dyslexic children have been shown to have atypical coordination of their brain's slower (delta and theta) rhythms with the cadence of speech, akin to a dance partner whose steps are misaligned with the rhythm of a song. The mechanism through which our brains align these automatic internal rhythms with external speech rhythms is termed "speech entrainment." This process, vital for speech comprehension, hinges on the perception of key landmarks (i.e., speech edges) in the speech signal, which occur particularly at the onset of words. Children with dyslexia often exhibit a reduced sensitivity to these speech cues, which could obstruct the synchronization of brain rhythms with the rhythm patterns of speech. In this investigation, we asked if this synchronization mechanism could be non-invasively manipulated to enhance dyslexic children's speech processing, by enhancing speech edge cues in speech. We designed a sophisticated algorithm to augment speech rhythm prominence in a children's story. We then measured brain activity using magnetoencephalography (MEG), a non-invasive method which measures magnetic fields of the brain, while children (8-9 years old) with- and without-dyslexia listened to a children’s story as either natural or enhanced speech. The neural effects of listening to natural versus enhanced speech were compared between groups. We found that children with dyslexia exhibited increased brain activity – relative to controls – when listening to enhanced speech. This brain activity originated in the bilateral auditory cortex. Furthermore, we discovered that the dyslexic brains automatically altered the ratio of brain activity between the theta and delta band, getting closer to a normative ratio. This discovery has many implications. One possibility is that prolonged exposure to enhanced speech may mitigate speech-brain asynchrony in dyslexia. Further, the ratio of activity in the theta and delta bands emerges as a potential target for non-invasive, non-pharmaceutical interventions in dyslexia such as brain-computer interfaces. Our findings further our understanding of dyslexia and open new avenues for intervention.

Find the paper here: doi: 10.3389/fnhum.2023.1200950

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