Worldwide, dyslexia is estimated to affect more than 10% of individual. It is a reading and spelling disorder caused by impairment of one’s ability to manipulate speech sounds. A new study has found evidence that the disorder is due to faulty wiring within the brain. A European team of researchers, headed by Bart Boets, PhD from KU Leuven in Belgium, published their findings on December 6 in the journal Science
The basic sounds of speech are known as phonemes. When a person hears spoken language or reads words, the brain produces a map of the phonemes; thus, allowing the person to distinguish between the sounds. However, this process is flawed in individuals with dyslexia. Two prevalent theories currently exist regarding dyslexia. One theory suggests that the problem is due to flawed sound representations in the brain; the other suggests that dyslexia is due to flawed wiring. Therefore, the researchers conducted a study to determine which theory explained the underlying cause of dyslexia.
The study group comprised 23 adults with dyslexia and a control group of normal adults. The researchers scanned the brains of the subjects with functional magnetic resonance imaging (fMRI). They were subjected to phonemes while the fMRI mapped their brains. The researchers found that the phonemes were stored on both sides of the brain in an area known as the auditory cortex. They found that these that the neural quality (in terms of strength and distinctness) was excellent in the subjects with dyslexia and was comparable to those without dyslexia. However, the functional and structural connectivity between the two auditory cortices and a brain are known as the left inferior frontal gyrus was significantly hindered in the dyslexics. The left inferior frontal gyrus is a region involved in higher-level sound processing. The researchers determined that this finding suggested deficient access to otherwise intact phonetic representations.
The researchers concluded that dyslexia is more likely to be due to a failure to connect to phonemes, rather than problems with the representations of the phonemes in the brain.
Take home message:
Although this study in itself did not offer a treatment for dyslexia, further understanding of a medical problem may eventually lead to effective treatment.
December 6, 2013