Shaping gamma oscillations through sensory stimulation: A systematic review in healthy adults.

Gamma-band brain activity (30-80Hz) plays a key role in sensory processing and cognitive functioning and is increasingly studied as a potential biomarker for neurological and psychiatric disorders. Recently, Gamma ENtrainment Using Sensory stimulation (GENUS) has emerged as a promising non-invasive approach to modulate this activity, with protocols targeting entrainment of intrinsic neural rhythms. However, substantial methodological variability persists across studies, limiting comparability and reproducibility. To better understand current practices and identify sources of heterogeneity, we reviewed 22 studies investigating gamma-band entrainment through visual, auditory, and multisensory stimulation in healthy adults. We summarized the main stimulation parameters and analytic methods used, discussed critical methodological challenges in evaluating entrainment efficacy, and proposed directions to improve standardization and interpretability. Our findings indicate that sensory modality, stimulus features (i.e., frequency, colour), and individual differences shape gamma responses and must be carefully controlled in research and clinical settings. Although 40Hz is the most frequently used frequency in entrainment studies, optimal effects varied across individuals and brain regions. Spatial patterns of activation also varied: visual stimulation primarily engaged occipital-parietal regions, auditory protocols extended to fronto-temporal areas, and multisensory paradigms elicited broader and sometimes superadditive responses. Promising stimulation strategies for enhancing both response strength and participant comfort include invisible flicker, sinusoidal tones, and cross-sensory stimulation. This review highlights important implications for developing therapeutic protocols such as GENUS and provides guidelines for the stimulation and measurement of gamma responses in experimental and clinical settings.