Does brain ability to synchronize with 40 Hz auditory stimulation change with age?

Auditory steady-state responses (ASSRs) are widely applied to test brain ability to follow external stimulation and this appeared to be a promising method in neuropsychiatric disorders. Nevertheless, there is no established conclusion on the way aging affects phase-locking measures of ASSRs in healthy subjects. We aimed to identify the effects of aging on phase-locking measures of 40 Hz ASSR. The effect of aging was tested in a sample of 46 healthy male subjects (20-58 years old) during eyes open condition. Stimuli were 500 ms trains, consisting of 20 identical clicks (1.5 ms burst of white noise) delivered binaurally. Time-frequency analysis of the data was performed and phase-locking index, evoked amplitude and total intensity measures were extracted and decomposed by non-negative multi-way factorization. As shown by curve-fitting analyses, phase-locking index and evoked amplitudes were diminishing with age in the linear manner. This was also proven by ANOVA testing when sample was divided into age groups. No effect of age on the total intensity was found. The complexity of the factors modulating the 40 Hz ASSR is not entirely solved; nevertheless, the current results suggest that the ability to synchronize to high frequency external stimulation diminishes with age. This should be taken into account, particularly when ASSRs are used in clinical practice, comparing patients and healthy subjects.