(a) At a group level, intrinsic timescale was correlated with local grey matter volume (GMV). Each circle represents an across-participant average of the intrinsic timescale and that of the GMV in one of the 360 brain regions defined by a previous multi-modal brain parcellation study (Glasser et al., 2016). Dotted lines and shaded areas indicate 95% confidence intervals of the fitted lines. (b) The correlation between the intrinsic timescale and GMV was significant even at a single-participant level. Each circle represents the Pearson’s correlation coefficient between the intrinsic timescale and GMV within each participant, which is calculated based on 360 brain areas (Glasser et al., 2016). (c) The correlation between the intrinsic timescale and GMV was seen in the four brain regions whose atypical intrinsic timescale was correlated with the severity of autism. Each circle represents an individual with ASD. Dotted lines indicate 95% confidence intervals of the fitted lines. (d) The GMVs of the three brain regions showing atypical reduction in the intrinsic timescale in autism were significantly smaller in the ASD than the TD group. In contrast, the GMV of the right caudate, which had an atypically longer intrinsic timescale in autism, was larger in the ASD group. (e) We conducted mediation analyses to examine the hypothesis that atypicality in the intrinsic timescale is one of the mediators linking atypical GMV and symptoms of autism. The analyses used the GMV, intrinsic timescale, and ADOS score as an independent variable, mediator variable, and dependent variable, respectively. ‘α” indicates effects of GMV on the intrinsic timescale, and ‘β” denotes effects of the intrinsic timescale on ADOS scores. ‘γ” represents direct effects of GMV on ADOS scores, and ‘α × β” indicates indirect effects. The statistical significance of the indirect effects (i.e., P values for ‘α × β”) and the insignificance of the GMV-ADOS direct effects (i.e., P values for ‘γ”) support the working hypothesis.