Stage 2 sleep and intelligence measures in autistic children

Abstract

Studies showed that sleep spindle activity correlate with IQ scores in typically developing individuals. Sleep spindles are diminished in children and adults with autism compared to typically developing individuals. We investigated the relationship between IQ scores and sleep spindles activity in children with autism. Thirteen boys with high functioning autism (HFA: 10.2 ± 2.1 years old) and 13 comparison children (COM: 10.2 ± 2.0 years old) were recorded for two consecutive nights. They completed the WISC-III in the morning after night 2. The absolute number of sleep spindles and spindle index (number/hour) sigma EEG power (slow: 12–13 Hz, fast 13.25–15.75 Hz) were recorded and computed from frontal (Fp1, Fp2) and central (C3, C4) electrodes during S2 sleep. Results from the two groups were compared using Student t-tests and Mann–Whitney U- tests. Correlations between EEG measure and IQ were tested using Pearson’s rho (alpha = .05). There were no group differences on IQ (HFA: Global = 105.2 ± 18.7, Performance = 106.2 ± 13.0, Verbal = 103.8 ± 22.3; COM: 115.8 ± 10.3, 114.1 ± 12.1, and 115.1 ± 12.8, respectively). Spindle number and index were lower in the HFA than the COM group at Fp2 electrode (669.7 ± 467.3 and 126.8 ± 87.1 vs. 1018.8 ± 466.4 and 216.2 ± 121.2). The HFA group showed a negative correlation between C3 spindles index in the first quarter part of the night and the WISC global ( r = −0.52) and verbal (C3 1/4 r = −0.62) scales. Sigma power was lower in the HFA than the COM group for C3 and C4 electrodes in the last quarter of the night (HFA: C3 = 0.925 ± 0.096, C4 = 0.650 ± 0.226; COM: C3 = 1.06 ± 0.18, C4 = 0.888 ± 0.301). The COM group showed a positive correlation between C4 fast Sigma activity in the last quarter of the night and global IQ ( r = 0.592). There were no significant correlation between IQ and Sigma activity in the HFA group. These findings indicate that the relationship between sleep EEG and IQ is different in autistic and typically developing children, both with normal IQ scores. These differences are in terms of scalp location (frontal vs. more posterior), EEG markers (spindles vs. Sigma activity) and time of night (early and late night). Supported by the Canadian Institutes of Health Research and the “Fonds de la recherche du Québec – Santé”.