Procedural Memory and Delta EEG Power during Nrem-Sleep in Young Typical and Autistic Adults

Background:  People with ASD are reported to perform poorly on sensory-motor procedural tasks when compared to typical participants (TYP). There is evidence suggesting that Stage 2 and Slow Wave Sleep (SWS) are linked to sensory-motor procedural learning. Moreover, Delta EEG activity, a slow EEG frequency band that characterizes SWS and that is also present during Stage 2, is thought to play a role in brain plasticity and formation of new learnings and memories.

Objectives:  We verified if a relation exists between Delta EEG power on one hand, and sensory-motor procedural learning and performance on the other hand in ASD and TYP adult participants.

Methods:  The sleep of 13 ASD and 14 TYP participants (22.1±3.8 and 21.5±3.6 years old, respectively) was recorded for 2 consecutive nights using a 22-electrode EEG montage. Spectral analysis of Delta (0.75-3.75 Hz) EEG power was obtained for stage 2 and SWS. A sensory-motor procedural task (Rotary Pursuit Task) was administered the morning following night 2. Learning and performance indices (i.e., increase of performance across trials and average performance for all trials, respectively) were calculated. Parametric and non-parametric correlation analyses were conducted to test the association between Delta EEG power during sleep and learning/performance.

Results:  In the TYP group, we found a significant positive correlation between the learning index and Delta relative power during stage 2 sleep all over the scalp (Fp1, Fp2, F7, F3, Fz, F4, F8, T7, C3, C4, T8, Tp7, P3, Pz, P4, Tp8, and O2) and during SWS for the frontal and the left temporal regions (Fp1, Fp2, F7, F8, T7, Tp7, and O2). In the ASD group, Delta relative power and learning were correlated within the frontal and the left temporal regions during stage 2 (Fp1, Fp2, F7, T7, Tp7, and P7); no significant correlation was found during SWS. A significant positive correlation was found between the performance index and Delta relative power during stage 2 (F3, Fz, F4, C3, C4, T8, Cp5, Cp6, P4, Tp8) in the ASD group only.

Conclusions: These results suggest that Delta activity during sleep facilitates learning a sensory-motor procedural task in TYP as well as in ASD groups of participants. Delta activity, however, is positively associated with performance only in ASD. It suggests that sensory-motor procedural learning and performance of people with ASD do not rely on the exact same neuronal networks than TYP participants.