Learning disabilities such as dyslexia are believed to affect nearly one in 10 children. To better study them, a Northwestern University research team has developed a data-driven conceptual framework that links two well-established scientific concepts. In doing so, they also have developed a non-invasive diagnostic tool called BioMAP that can quickly identify children with learning disabilities.
Scientists have long recognized that children who can best process various aspects of the sounds of language are more likely to read earlier and develop into better readers and writers than those who cannot. After a decade of research, Northwestern Professor Nina Kraus and her colleagues have discovered a subset of learning disabilities that results from a dysfunction in the way the brainstem encodes certain basic sounds of speech.
In an article in the April "Trends in Neurosciences," Kraus, who is Hugh Knowles Professor of Communication Sciences and Neurobiology, and senior research analyst Trent Nicol for the first time ever have linked the source-filter model of acoustics with the cerebral cortex's "what" and "where" pathways via the auditory brainstem.
The research they present in "Trends" represents the theoretical underpinning for BioMAP, the simple neurophysiological test that can identify children with sound processing disorders. Kraus's laboratory, in partnership with Bio Systems Corp., will soon make the diagnostic tool available in the marketplace.
BioMAP objectively measures whether a child's nervous system can accurately translate a sound wave into a brain wave. If it cannot, the affected individual -- like nearly a third of the language-disordered children Kraus has studied -- demonstrates problems in discriminating speech sounds that interfere with normal learning. Once identified, children with these problems will be able to improve their speech discrimination skills through auditory training.
Early in her work -- because the deficits she was exploring related to the complex processes of reading and writing -- Kraus studied how the cortex, the part of the brain responsible for thinking, encoded sound. She and her colleagues now understand that problems associated with the encoding of sound can also occur earlier and lower in the auditory pathway in the brainstem. After analyzing years of data, they have discovered that, when recorded, the brain waves generated at the brainstem level in non-learning disabled children can look almost identical to the sound wave itself. In contrast, the brain waves of language-impaired children look somewhat different from the sound wave, showing evidence of what Kraus calls a "jitter" in the encoding process. In a perfectly functioning system, a given sound will unfailingly induce a neuron to fire a precise number of milliseconds later. In a disordered system, however, the timing of these firings can vary markedly.
"We record the averaged activity of large numbers of neurons," Kraus explains. "If the neurons are not firing when they should, the response gets blurred." She has found a "jitter" in the brainstem's filter-class response (its response to the linguistic content of a sound wave) while its source-class response (its response to the non-linguistic aspects of speech, such as intonation, emotion, pitch and inflection) appears normal.