12/03/2025
Although infraslow frequencies (ISF) represent the largest and most powerful portion of the brain’s electrophysiological spectrum, their scientific development lagged for decades due to historical, technical, and cultural barriers—from Cold War isolation and untranslated Russian research to early EEG technologies that filtered out slow signals entirely. Yet from Aladjalova’s pioneering observations in the 1950s to modern digital-era breakthroughs, a consistent picture has emerged: ISFs reflect slow shifts in cortical excitability, shape the amplitude and coordination of faster rhythms, and synchronize distant brain regions through scale-free, power-law dynamics. As recording technologies improved, studies revealed that ISFs modulate perception, regulate cross-frequency coupling, and organize the activity of large-scale brain networks such as the Default Mode Network. These discoveries reposition ISF not as a peripheral curiosity but as a foundational control signal—one that likely underlies the dynamic switching, integration, and competition among the brain’s major functional networks. This sets the stage for understanding ISF within the Triple Network Model, where the Default Mode, Salience, and Executive Control networks rely on slow-timescale coordination to support healthy cognition—and where disruptions in ISF may help explain network-level dysfunction in psychopathology.
