Slow-Wave EEG Activity During Sleep In Adults with Autistic Spectrum

Background: Polysomnographic recordings show that the sleep of autistic adults is characterized by low amounts of nonREM sleep (stages 2+3+4), including diminished Slow Wave Sleep (SWS: stages 3+4) (Limoges et al., 2005). The main polysomnographic feature of nonREM sleep is Delta activity, a low frequency EEG signal peaking over frontal recording sites. Delta EEG activity is thought to reflect at least three characteristics of the cortex: synaptic density, maturity, and metabolic rate (Feinberg et al., 1990).

Objectives: To map the quantified slow wave EEG activity of autistic adults during nonREM across the scalp using a full EEG montage in order to verify its amplitude and distribution vs. a group typically developed individuals.

Methods: Sixteen autistic adults (ASD: 15 M, 1 W, 22.0±3.8 years old) and 18 comparison participants (COM: 17 M, 1 W, 21.0±4.2 years old) were recorded for two consecutive nights in a sleep laboratory using a 19 recording electrodes (Fp1, Fp2, Fz, F3, F4, F7, F8, Cz, C3, C4, T7, T8, Pz, P3, P4, P7, P8, O1, O2). Spectral amplitude of nonREM Delta EEG activity (0.75-3.75 Hz) was computed for the first seven hours of sleep of night 2; analysis of EEG during SWS was restricted to the first hour of the night, due to its natural temporal distribution. Groups were compared using one-way ANOVAs, with a significance level set at .05, in two separate sets: 1) The seven frontal electrodes; 2) The remaining electrodes.

Results: 1) Frontal EEG activity. When considering the total amount of nonREM sleep during the first 7 hours of the night, Delta EEG activity was significantly *decreased* for ASD compared to controls for Fz (ASD=2.7±0.06, COM=2.9±0.06) and F3 (ASD=2.7±0.06, COM=2.8±0.06). A closer stage-by-stage analysis (comparing groups on stages 2, 3 and 4 separately) showed that differences were restricted to stage 2; moreover, this analysis disclosed *increased* Delta activity for the F7 electrode in the ASD groups (ASD=296.13±52.06, COM=158.22±11.43) and a same trend at T7. 2) Remaining electrodes. The analysis of Delta EEG over more posterior recording sites disclosed a decreased activity over C3, C4, Pz, P3, P4, O1 and O2 both during stage 2 and SWS.

Conclusions: Delta activity during nonREM sleep is *decreased* over most of the recording sites of the ASD group while it is *increased* over the left temporal lobe (F7, P7). These results further support the hypothesis of an atypical cortical connectivity in ASD, possibly due to altered synaptic density, maturity, or due to altered cortical metabolic rate during nonREM sleep.