Developmental and aging trajectories of 40-Hz auditory steady-state responses: A systematic review across the human...

Auditory steady-state responses (ASSRs) are rhythmic neural oscillations that synchronize to periodic auditory stimulation and serve as a noninvasive index of cortical network dynamics. ASSRs, particularly those at 40 Hz, have received substantial attention as sensitive markers of temporal precision, excitation-inhibition balance, and functional connectivity in the auditory cortex, and have been widely applied in translational research on neurodevelopmental and neuropsychiatric disorders. Because gamma synchronization supports key cognitive functions, including auditory temporal processing, selective attention, speech perception, and early language development, mapping its lifespan trajectory provides insight into how maturing cortical dynamics underpin cognitive development. However, despite extensive clinical use, the normative developmental and aging trajectory of gamma-range ASSRs remains unclear. This systematic review aimed to synthesize evidence on age-related differences in ASSRs measured with EEG or MEG across the human lifespan. Following PRISMA guidelines, searches were conducted in PubMed/Scopus, identifying 40 eligible studies. The findings reveal a pronounced increase in ASSR amplitude and phase-locking from infancy through adolescence, consistent with maturation of inhibitory circuitry, synaptic refinement, and myelination. In adulthood and aging, results were heterogeneous, with studies reporting preserved, diminished, or enhanced 40-Hz synchronization, reflecting diverse methodological approaches and potentially distinct neurobiological changes. Lifespan coverage across studies was uneven, with sparse data in early childhood and older adulthood, and limited longitudinal evidence. The review suggests a nonlinear trajectory characterized by developmental strengthening, adult stability, and variable age-related change. Comprehensive lifespan-spanning and longitudinal studies are needed to establish normative patterns and improve the interpretability of ASSR alterations in clinical populations.