Like typically developing children, girls with Rett syndrome can distinguish known words from meaningless non-words when spoken to, but may do so using potentially peculiar neural processes, compared with their peers, according to a study.
The research, “Spoken word processing in Rett syndrome: Evidence from event-related potentials ,” was published in International Journal of Developmental Neuroscience.
Rett syndrome is a neurodevelopmental disorder that affects girls almost exclusively, and the way their brains develop, causing a progressive loss of motor skills and speech.
It is challenging to directly test the listening-based (as opposed to reading-based) language ability in individuals with limited speech and motor skills due, in part, to the difficulties in administering conventional psychological tests that typically require hand use or spoken responses. Therefore, conventional tests cannot capture the full range of listening-based language ability in children with Rett syndrome, or other developmental disabilities.
Therefore, event-related potentials have been successfully implemented in studies to document language skills, predict developmental outcomes, and provide evidence of treatment effects without relying on participants’ movements. Event-related potentials measure brain responses directly resulting from a specific sensory, cognitive, or motor event.
Previous studies have shown that during spoken word processing in typically developing children, event-related potentials are sensitive to differences between known words and non-words (i.e. scrambled or backward words).
These studies identified a brain activity signature representative of listening-based language processing. By 20 months of age, a child’s signature consists of unique event-related-potential signals in the left side of the temporal and parietal lobes of the brain, which respond with greater negative intensity (amplitudes) to words than non-words.
The brain is divided into four different lobes, all connected to different brain functions. The temporal lobe is involved in processing sensory input to retain visual memories, language comprehension, and emotion association; the parietal lobe integrates sensory information — including spatial sense and navigation, and sense of touch — and is involved in language processing.
In the study, researchers at Vanderbilt University Medical Center used auditory event-related potentials to evaluate spoken word processing during passive listening in girls with Rett syndrome and typical peers.
Eleven girls with Rett syndrome, ages 4 to 11, participated in the study, and were compared with 33 typically developing children, 4 to 12 years old.
The researchers found that both groups demonstrated the expected, more negative, event-related-potential amplitude to words than non-words. However, this response was observed at left temporal sites in the typically developing children, but the signal was predominantly detected in right temporal sites in girls with Rett syndrome.
Furthermore, in girls with Rett syndrome, better communication abilities was linked to more typical event-related-potential responses to words (greater negative signal intensity at left temporal sites), which was associated with better receptive communication abilities, reduced social withdrawal, and decreased irritability.
These results highlight the usefulness of auditory event-related potentials to directly evaluate, and characterize speech and language processes in Rett syndrome, and other developmental disorders that limit speech.
The researchers hope that one day these kinds of event-related-potential signatures will be used to characterize outcomes of clinical trials, such that the effectiveness of a treatment can be evaluated by its ability to restore a typical signature.
“Our study is the first to examine spoken word comprehension in Rett syndrome,” the researchers wrote. “These results provide a strong rationale for using event-related-potentials during passive listening to spoken words as a marker of auditory content processing in participants with Rett syndrome or other developmental disabilities for whom few optimized standardized behavioral assessments of language exist.”
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