NREM sleep EEG activity and procedural memory: A comparison between young neurotypical and autistic adults without sleep complaints.

Delta EEG activity (0.75-3.75 Hz) during non-Rapid eye movement (NREM) sleep reflects the thalamo-cortical system contribution to memory consolidation. The functional integrity of this system is thought to be compromised in the Autism spectrum disorder (ASD). This lead us to investigate the topography of NREM sleep Delta EEG activity in young adults with ASD and typically-developed individuals (TYP). The relationship between Delta EEG activity and sensory-motor procedural information was also examined using a rotary pursuit task. Two dependent variables were computed: a learning index (performance increase across trials) and a performance index (average performance for all trials). The ASD group showed less Delta EEG activity during NREM sleep over the parieto-occipital recording sites compared to the TYP group. Delta EEG activity dropped more abruptly from frontal to posterior regions in the ASD group. Both groups of participants learned the task at a similar rate but the ASD group performed less well in terms of contact time with the target. Delta EEG activity during NREM sleep, especially during stage 2, correlated positively with the learning index for electrodes located all over the cortex in the TYP group, but only in the frontal region in the ASD group. Delta EEG activity, especially during stage 2, correlated positively with the performance index, but in the ASD group only. These results reveal an atypical thalamo-cortical functioning over the parieto-occipital region in ASD. They also point toward an atypical relationship between the frontal area and the encoding of sensory-motor procedural memory in ASD. Autism Res 2018, 11: 613-623. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Slow EEG waves recorded from the scalp during sleep are thought to facilitate learning and memory during daytime. We compared these EEG waves in young autistic adults to typically-developing young adults. We found less slow EEG waves in the ASD group and the pattern of relationship with memory differed between groups. This suggests atypicalities in the way sleep mechanisms are associated with learning and performance in a sensory-motor procedural memory task in ASD individuals.

Increased topographical variability of task-related activation in perceptive and motor associative regions in adult autistics.

BACKGROUND: An enhanced plasticity is suspected to play a role in various microstructural alterations, as well as in regional cortical reallocations observed in autism. Combined with multiple indications of enhanced perceptual functioning in autism, and indications of atypical motor functioning, enhanced plasticity predicts a superior variability in functional cortical allocation, predominant in perceptual and motor regions. METHOD: To test this prediction, we scanned 23 autistics and 22 typical participants matched on age, FSIQ, Raven percentile scores and handedness during a visuo-motor imitation task. For each participant, the coordinates of the strongest task-related activation peak were extracted in the primary (Brodmann area 4) and supplementary (BA 6) motor cortex, the visuomotor superior parietal cortex (BA 7), and the primary (BA 17) and associative (BAs 18 + 19) visual areas. Mean signal changes for each ROI in both hemispheres, and the number of voxels composing the strongest activation cluster were individually extracted to compare intensity and size of the signal between groups. For each ROI, in each hemisphere, and for every participant, the distance from their respective group average was used as a variable of interest to determine group differences in localization variability using repeated measures ANOVAs. Between-group comparison of whole-brain activation was also performed. RESULTS: Both groups displayed a higher mean variability in the localization of activations in the associative areas compared to the primary visual or motor areas. However, despite this shared increased variability in associative cortices, a direct between-group comparison of the individual variability in localization of the activation revealed a significantly greater variability in the autistic group than in the typical group in the left visuo-motor superior parietal cortex (BA 7) and in the left associative visual areas (BAs 18 + 19). CONCLUSION: Different and possibly unique strategies are used by each autistic individual. That enhanced variability in localization of activations in the autistic group is found in regions typically more variable in non-autistics raises the possibility that autism involves an enhancement and/or an alteration of typical plasticity mechanisms. The current study also highlights the necessity to verify, in fMRI studies involving autistic people, that hypoactivation at the group level does not result from each individual successfully completing a task using a unique brain allocation, even by comparison to his own group.

Atypical processing of auditory temporal complexity in autistics.

Autistics exhibit a contrasting combination of auditory behavior, with enhanced pitch processing abilities often coexisting with reduced orienting towards complex speech sounds. Based on an analogous dissociation observed in vision, we expected that autistics' auditory behavior with respect to complex sound processing may result from atypical activity in non-primary auditory cortex. We employed fMRI to explore the neural basis of complex non-social sound processing in 15 autistic and 13 non-autistics, using a factorial design in which auditory stimuli varied in spectral and temporal complexity. Spectral complexity was modulated by varying the harmonic content, whereas temporal complexity was modulated by varying frequency modulation depth. The detection task was performed similarly by autistics and non-autistics. In both groups, increasing spectral or temporal complexity was associated with activity increases in primary (Heschl's gyrus) and non-primary (anterolateral and posterior superior temporal gyrus) auditory cortex Activity was right-lateralized for spectral and left-lateralized for temporal complexity. Increasing temporal complexity was associated with greater activity in anterolateral superior temporal gyrus in non-autistics and greater effects in Heschl's gyrus in autistics. While we observed similar hierarchical functional organization for auditory processing in both groups, autistics exhibited diminished activity in non-primary auditory cortex and increased activity in primary auditory cortex in response to the presentation of temporally, but not of spectrally complex sounds. Greater temporal complexity effects in regions sensitive to acoustic features and reduced temporal complexity effects in regions sensitive to more abstract sound features could represent a greater focus towards perceptual aspects of speech sounds in autism.