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

## TL;DR

This review examines how 40-Hz auditory steady-state responses change across the human lifespan, highlighting key developmental patterns and gaps in current research.

## Contribution

The paper provides a systematic synthesis of age-related changes in 40-Hz ASSRs, revealing nonlinear developmental and aging trajectories.

## Key findings

- ASSR amplitude and phase-locking increase significantly from infancy to adolescence.
- Adult and aging studies show inconsistent results, likely due to methodological differences.
- Sparse data in early childhood and older adulthood limit understanding of full lifespan patterns.

## Abstract

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.

•ASSRs show strong maturation from infancy to adolescence.•Adult ASSR findings vary across studies.•Aging effects on 40-Hz ASSRs are heterogeneous and non-linear.•Lifespan coverage in ASSR research remains incomplete.•More longitudinal studies are needed for normative trajectories.

ASSRs show strong maturation from infancy to adolescence.

Adult ASSR findings vary across studies.

Aging effects on 40-Hz ASSRs are heterogeneous and non-linear.

Lifespan coverage in ASSR research remains incomplete.

More longitudinal studies are needed for normative trajectories.