Infraslow generation and transmission shape BOLD connectivity in neural mass models

Resting-state functional connectivity (FC) is measured from slow blood-oxygen-level-dependent (BOLD) fluctuations, but their origin and its consequences for FC remain unresolved. We compared two sources of infraslow activity (ISO; 0.01–0.1 Hz) in pyramidal–interneuron gamma (PING)-like neural-mass networks: autonomous gamma interactions in noise-free networks (PING⁺) and regionally independent external noise in locally damped networks (PING⁻). Group-average Human Connectome Project diffusion-MRI structural connectivity (SC) and resting-state FC, distributed through the ENIGMA Toolbox, supplied the 82-region network and empirical benchmark. Frequency-selective interventions, calibrated Stuart–Landau (SL) comparators and BOLD decomposition separated generation from transmission. In PING⁺, carrier interventions and temporal prediction supported ISO generation by gamma beating. Converting beating between nearby gamma rhythms into a slow rate component requires even-order mixing, supplied here by the sigmoid and omitted from the first-order SL comparison. This endogenous source is constrained by SC, circuit parameters and tonic inputs; the coupled-equilibrium linearization contained no slow modes. In PING⁻, noise prescribes the ISO input and neural ISO persists without gamma exchange. Both regimes produced SC-aligned FC, but their FC patterns differed, and PING⁺ showed stronger empirical correspondence at the tested operating points and record lengths. With first-order transmitted rates and readout, noise-free SL⁺ produced negligible ISO, whereas noise-driven SL⁻ retained ISO and structural alignment. Suppressing ISO transmission preserved approximately 75% and 92% of BOLD power in PING⁺ and PING⁻, respectively, but removed observed FC–SC alignment and weakened empirical correspondence. All in all, our results show that PING⁺ generates ISO through intrinsic gamma beating and even-order sigmoid mixing, whereas PING⁻ receives ISO through external noise; in both regimes, ISO transmission shapes BOLD FC.