Frequency optimisation for entrainment of gamma waves via sound stimulation in older adults

Gamma-band neural oscillations, mechanistically associated with higher-order cognitive functions, may weaken with age. The observation of aberrant gamma rhythms in cognitive decline indicates their potential as a biomarker for Alzheimer’s disease. In turn, research demonstrates that manipulation of oscillations via neuromodulatory techniques may rescue cognition and attenuate dementia-related pathology. Promising findings from preclinical studies indicating that sensory gamma stimulation offers neuroprotective effects and preliminary results from human trials support the efficacy of sensory entrainment in slowing decline, with optimisation of stimulation parameters suggested as the next milestone for increasing impact. Although 40-Hz stimulation is typical, evidence suggests the frequency for optimal gamma entrainment may decrease with advancing age. In an exploratory design, we sought to determine if 40-Hz auditory stimulation can be deemed optimally effective for gamma entrainment in older adults. Electroencephalography (EEG) recordings taken from 15 healthy volunteers (aged 60 to 75 years) during auditory stimulation at gamma frequencies ranging from 37-45 Hz in 1-Hz increments were analysed to characterise individual differences in entrainment. Individual optimal stimulation frequencies elicited significantly stronger entrainment in comparison to 40 Hz, supporting the potential value of fine-tuning stimulation parameters to enhance therapeutic effects of gamma entrainment in clinically relevant populations.