<p>Quantifying intrinsic timescale using autocorrelation function.</p>

We estimated an autocorrelation function (ACF) for the normalized (i.e., z-scored) time series. Intrinsic timescale was then quantified as the sum of positive autocorrelation values (ac > 0; colored parts of the ACFs above) multiplied by TR for each cortical region and individual.

This is approximately equivalent to calculating the area under the curve of the positive part of the ACF curve (i.e., shaded areas). As demonstrated in the example plots, a fast-decaying ACF will have shorter memory, and thus a shorter timescale (orange region and ACF plot), compared to a slow-decaying ACF (purple region and ACF plot). Data and code needed to regenerate this figure can be found at <a href="doi.org/10.5281/zenodo.22799416" target="_blank">doi.org/10.5281/zenodo.22799416</a>.</p>