A new study from Italy analyzed the sleep of 16 children with developmental dyslexia. The results were published in the Oct. 1 issue of the journal Sleep.
The children had an average age of 11 years. Their sleep was evaluated during an overnight sleep study in a sleep lab. Results were compared with 11 children who read normally.
The study found that dyslexic children had a higher percentage of light, stage 2 sleep; they had a lower percentage of deep, slow wave sleep. These stages occur during non-rapid eye movement sleep – or NREM sleep. Children with dyslexia also had fewer periods of REM sleep.
Further analysis found additional differences during stage 2 sleep. Children with dyslexia had an increase in the power of fast, “sigma” brain waves; they also had an increased “sleep spindle” density. There were positive correlations between these measures and the children’s performance on reading tests.
A sleep spindle is a brief burst of rhythmic brain activity; it is a unique aspect of stage 2 sleep. “Density” refers to the number of sleep spindles that occur per minute of stage 2 sleep.
Dyslexic children had an average of 6.2 sleep spindles per minute; normal readers had only 3.5 sleep spindles per minute.
The NINDS reports that dyslexia is a brain-based type of learning disability; it involves a reading impairment that occurs in a person who has normal intelligence.
The authors suggest that increases in sleep spindles and sigma power may be markers of dyslexia; these markers may be related to the severity of reading impairment. The results also support the hypothesis that sleep plays an important role in learning and memory.
The authors note that only one other study has measured brain activity during sleep in children with reading disabilities; the results were published in the journal Sleep in 1993. That study found similar changes in the sleep of reading-disabled boys.
Learn more about sleep stages on SleepEducation.com.
Image by Shanubi