The auditory steady-state response (ASSR) is your brain's tendency to synchronize its electrical activity to the rhythm of a repeating sound. Play a tone that pulses 10 times a second, and EEG recordings show brain activity starting to pulse at close to that same rate. It is often called the frequency-following response; strictly, that name belongs to a related brainstem effect.
This is the mechanism behind brainwave entrainment generally, and behind every FMB sound journey specifically: pick a target rhythm, play it consistently, let the ASSR do the rest. It's a well-documented EEG/MEG phenomenon; how strongly it translates into a specific subjective effect (calmer, more focused) varies by person and by study. Full citations: Read the Research.
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