14 DAY TRIAL // In a new study, investigators from the Ecole Normale Superieure in Paris, France, managed to determine the specific brain abnormality that underlies the development of dyslexia. The team learned that auditory signal processing pathways display a glitch that is the most likely cause of the condition.
The findings are in tune with past studies, which did suggest that the improper processing of speech and associated sounds is somehow related to the development of reading disorders. The condition mostly affects children, which is why researchers are so keen on developing new treatments.
Experts are quick to point out that this is most likely not the only cause of dyslexia. Other than an impaired ability to read, the condition also causes difficulty in keeping up with rapid naming, in understanding orthographic coding, and also with auditory short-term memory.
In the new investigation, experts established that the problem lies in the left auditory cortex of people suffering from dyslexia. The usual auditory rhythm processing patterns were severely disrupted in this specific area of the brain, and the change was only specific to patients suffering from this condition.
“It is widely agreed that for a majority of dyslexic children, the main cause is related to a deficit in the processing of speech sounds,” ENS Auditory Language Group researcher and senior study author Anne-Lise Giraud, PhD, explains.
“It is also well-established that there are three main symptoms of this deficit: difficulty paying attention to individual speech sounds, a limited ability to repeat a list of pseudo-words or numbers, and a slow performance when asked to name a series of pictures, colors, or numbers as quickly as possible,” she says.
An interesting discovery the team made was that the dyslexic brain sometimes appeared to exhibit an enhanced response to high-frequency rhythms, for which researchers could not account. This phenomenon interfered with verbal memory skills indirectly.
Scientists refer to this as “oversampling,” as opposed to standard sampling. The latter occurs when we hear something, and break down the sound in its smallest components, for easier processing. When this is done excessively, our perception of speed sounds may also get distorted.
Details of the new investigation appear in the latest issue of the esteemed scientific journal Neuron, PsychCentral reports.
“Our results suggest that the left auditory cortex of dyslexic people may be less responsive to modulations at very specific frequencies that are optimal for analysis of speech sounds and overly responsive to higher frequencies, which is potentially detrimental to their verbal short-term memory abilities,” Giraud concludes.