Ethnicity may affect the level of working memory function in young adults with insomnia or restless legs syndrome.
MINNEAPOLIS—African Americans who have insomnia or symptoms of restless legs syndrome (RLS) have a significantly lower working memory capacity than Caucasians with insomnia and normal sleepers regardless of their ethnicity, according to research presented at the 25th Anniversary Meeting of the Associated Professional Sleep Societies.
“This study shows that the ability to engage in an attention-demanding memory task is more compromised among participants with RLS symptoms, and insomnia particularly, in Africans Americans compared with Caucasians within a self-reported healthy, young adult college sample,” reported graduate student Megan E. Ruiter and Kenneth L. Lichstein, PhD, Director of the Sleep Research Project, Department of Psychology, both at the University of Alabama in Tuscaloosa. “The implication of this study might be that treatment outcomes for African Americans with insomnia or RLS may need to emphasize improvement in cognitive functioning.”
Neurocognitive Deficits and Sleep Disorders
The researchers conducted an online survey of 1,277 college students to determine whether working memory capacity varied between normal sleepers and persons with a suspected sleep disorder, as well as whether those differences were moderated by ethnicity. All participants also completed an online working memory task.
The mean age of the sample (311 males) was 19.4; 1,078 participants were Caucasian, and 199 were African American. A total of 98 participants had previously been diagnosed with a mental disorder, and the overall mean BMI of the cohort was 23.6.
The researchers used the Automated Operation Span task to gauge working memory capacity and the Insomnia Severity Index to quantify perceived sleep difficulty and severity of insomnia. The Global Sleep Assessment Questionnaire was used to screen for the presence or absence of insomnia, obstructive sleep apnea, RLS, periodic limb movements, and parasomnias.
Participants were designated as having insomnia if they met all International Classification of Sleep Disorders-II (ICSD-II) criteria and had a score of 8 or greater on the Insomnia Severity Index. Subjects were classified as having other suspected sleep disorders if they experienced symptoms of each sleep disorder “usually” or “always.” In addition, students were regarded as normal sleepers if they “never” or “sometimes” had symptoms indicative of a sleep disorder and were not diagnosed with a mental disorder.
Sleep, Memory, and Ethnicity
Among the participants, 34.7% were normal sleepers, 24.8% had insomnia per the ICSD-II, 6% had RLS, 5.3% had periodic limb movements, and 4.2% had parasomnias, and 1.3% had obstructive sleep apnea symptoms.
After adjusting for age, gender, BMI, global health status, and mental disorder diagnosis, the investigators found no significant differences in working memory capacity when they compared normal sleepers with students who had RLS, periodic limb movements, obstructive sleep apnea symptoms, parasomnias, and insomnia. However, “there were significant interaction effects between ethnicity and RLS symptoms and insomnia,” noted the study authors.
“Future research should focus on the mechanisms underlying the ethnic–working memory relationship among these sleep-disordered populations,” the researchers concluded.
—Colby Stong