Resting-state alpha in autism spectrum disorder and alpha associations with thalamic volume

Abstract

Alpha circuits (8-12 Hz), necessary for basic and complex brain processes, are abnormal in autism spectrum disorder (ASD). The present study obtained estimates of resting-state (RS) alpha activity in children with ASD and examined associations between alpha activity, age, and clinical symptoms. Given that the thalamus modulates cortical RS alpha rhythms, associations between thalamic structure and alpha activity were examined. RS magnetoencephalography was obtained from 47 typically-developing children (TDC) and 41 children with ASD. RS alpha activity was measured using distributed source localization. Left and right thalamic volume measurements were also obtained. In both groups, the strongest alpha activity was observed in Calcarine Sulcus regions. In Calcarine regions, only TDC showed the expected association between age and alpha peak frequency. ASD had more alpha activity than TDC in regions bordering the Central Sulcus as well as parietal association cortices. In ASD, whereas greater left Central Sulcus relative alpha activity was associated with higher Social Responsiveness Scale (SRS) scores, greater Calcarine region relative alpha activity was associated with lower SRS scores. Although thalamic volume group differences were not observed, relationships between thalamic volume and Calcarine alpha power were unique to TDC. The present study also identified a failure to shift peak alpha frequency as a function of age in primary alpha-generating areas in children with ASD. Findings suggested that increased RS alpha activity in primary motor and somatosensory as well as parietal multimodal areas-with increased alpha thought to reflect greater inhibition-might impair the ability to identify or interpret social cues. Finally, to our knowledge, this is the first study to report associations between thalamic volume and alpha power, an association observed only in TDC. The lack of thalamic and alpha associations in ASD suggests thalamic contributions to RS alpha abnormalities in ASD.

Fig. 1

VESTAL relative alpha power group-difference maps. Best seen in the coronal views (lower row), in both groups the strongest relative alpha activity was observed in primary visual areas (TDC shown in red on the left, ASD shown in blue in the center). No group differences were observed in primary alpha generator areas. Rather, the statistics map (third column) shows greater relative alpha power in ASD than TDC in regions bordering Central Sulcus and parietal-occipital regions (shown in yellow; p < 0.05, familywise corrected). The figure spectrum plot shows the TDC (red) and ASD (blue) relative power spectrum from 1 to 50 Hz for the Central Sulcus and Calcarine region ROIs (alpha range highlighted in gray; for each frequency bin, mean values obtained by averaging across voxels in each ROI for each frequency bin) (Color figure online)

Fig. 2

Areas showing associations between relative alpha power and SRS scores in the children with ASD are shown in yellow and purple (p < 0.05, familywise corrected). The scatterplot shows that whereas higher SRS scores were associated with increased left-hemisphere Central Sulcus relative alpha activity (top row—shown in yellow), lower SRS scores were associated with increased Calcarine region relative alpha activity (bottom row—shown in purple) (Color figure online)

Fig. 3

Scatterplots showing for each group associations between left and right thalamic volume (x axis) and Calcarine region relative alpha power (y axis). Correlation r-values are shown in the top left of each plot (* p < 0.05; ** p < 0.01). Although hierarchical regressions indicated similar associations between thalamic volume and relative alpha power in ASD and TDC (via a non-significant interaction term), the scatterplots show associations between thalamic volume and relative alpha power only in TDC. The lack of a significant interaction term in the regression is likely due to insufficient power