Functional correlates of brain aging: beta and gamma components of event-related band responses

The brain as a system with gradually declining resources by age maximizes its performance by neural network reorganization for greater efficiency of neuronal processes which is reflected in changes of event-related band responses (ERBRs) for sensory stimuli. Whether changes of high-frequency components of event-related responses are related to plasticity in neural recruitment during stabilization of sensory/cognitive mechanisms accompanying aging or are underlying pathological changes remains unknown. The effect of aging on beta (β1: 12.5–20; β2: 20.5–30 Hz) and gamma (γ1: 30.5–49; γ2: 52–69 Hz) band components of ERP was studied in an auditory discrimination task (low-frequency and high-frequency tone) at frontal, central, parietal and occipital cortical locations at short latency (post-stimulus interval 0–250 ms; putative sensory processing) and long latency (250–600 ms; putative cognitive) periods. Beta1 component of the short latency period of ERBRs was less affected by age. The beta1 activity of the long latency period was reduced by age and more widespread than in the short latency period. The aged difference in beta1 component spread into fronto-parietal regions and was more expressed after high-frequency than after low tone stimulation. Beta2 and gamma amplitudes were higher with progressive age during sensory processing. Reducing regional-process specificity with progressing age characterized tone-dependent beta2 changes during short latency (sensory), but not during long latency (cognitive) processing. Late latency (cognitive) beta2 and gamma activity diminished with age, except for the frontal high tone responses. With increasing age, gamma2 activity was more expressed over the frontal brain areas in high tone discrimination. We concluded that age influenced more the long latency (cognitive) processes than the short latency (sensory) ones.