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

Abstract

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.

Do the Changes of Event-Related Potentials and Frequency Band Responses to Sensory Stimuli Correlate to Age Cognitive Decline?

“…Functional differences are found between high-frequency eventrelated oscillatory activity in sensory-motor information processing of elderly and young subjects in both stimulus encoding and cognitive processing [31] .…”

“…The beta activity is implicated in attention, perception, initiation and motor planning [31,52] , and also correlates with the long-range synchronous activity of neocortical regions [53] . The lower β1activity in the elderly than in the young subjects during the sensory processing of high tone stimulation might reflect an attentional shift towards the high-frequency acoustic stimuli.…”

“…Event-related oscillatory responses in different frequency bands are modulated by sensory and cognitive processes and with the age [30,31] . Widespread enhanced delta and theta activity for elderly subjects are present during the sensory processing independent of a tone type [30] .…”

“…Cognitive β1 changes in the elderly lag as compared to the young subjects. Thus, the age-related β1oscillation differences in the central brain areas might reflect stronger β1 event-related desynchronization (ERD) effect on the adult subjects when the movement is involved [31,52] . Beta frequency responses (mainly ERD) have also been associated with an auditory memory [49,54] , cognitive control of behavior or "executive functions" [55] .…”

“…The appearance of agerelated β2 differences at the task end corresponds to different extents of beta rebound response with increasing age. The beta rebound effect may reflect an age-dependent inhibitory process of the primary motor cortex and this decreased motor inhibition may facilitate neuronal plasticity and promote motor learning [31,52] .…”