Meaningful neural activation modulations are happening across a wide range of temporal frequencies. While depth-dependent electrophysiology studies often focus on the modulation of neural activity, connectivity and phase amplitude coupling changes in the range of 50 ms – 300 ms (Godlove et al. 2014; Sotero et al. 2015), optical imaging studies examine meaningful resting-state connectivity across from the regime of 100 ms up to the 10 s regime (Ma et al. 2016). Due to the hemodynamic delay of the vascular response, conventional resting-state fMRI focuses on signal fluctuations in the time frame of 6–10 s3, implying that fMRI is usually only sensitive to a small frequency window of a wide spectrum of neural fluctuations. The acquisition approaches for whole brain layer-dependent connectivity analyses discussed in Figs. 1C, 3, and 7, are optimized for this temporal frequency window of ≥10s. Since resting-state fMRI fluctuations follow the pattern of scale free dynamics (He 2011), the focus on this frequency window is expected to be largely representative of functional connections at any temporal scales. Future work in combining the MAGEC-VASO approach with acceleration in both phase-encoding directions (Huber et al. 2020a) will become important to confirm this temporal invariance.
