Gamma oscillations weaken with age in healthy elderly in human EEG

Stimulus-induced Gamma rhythms are weaker in human elderly with Mild Cognitive Impairment and Alzheimer’s Disease

“…We found that the cases and their respective controls had comparable eye-movement and microsaccade profiles, and similar pupillary reactivity to stimulus presentation (measured as coefficient of variation of pupil diameter across time, see 17). Further, the trends described in Figures 1 and 2 did not change when we reanalysed the data after removing stimulus repeats containing microsaccades (17,27, see SI Methods) from analysis ( Supplementary Figure 3). Finally, the cases and controls had comparable PSDs and slopes of PSDs in the baseline condition ( Supplementary Figure 4).…”

“…We averaged spectral data for all analyzable bipolar electrodes (as described in 17) from 10 occipital and parieto-occipital pairs (marked in black enclosures in Figure 1d; see SI Methods). Figure 1a shows the median stimulus-induced change in PSDs for 20 cases and 114 age and gender matched controls pooled together (light shaded regions show ±SD of median after bootstrapping for 10,000 iterations).…”

“…Age is as a common factor that influences both macroscopic structure (45)(46)(47) as well as gamma power and frequency (17).…”

“…Recent studies in human EEG (16,17) and MEG (18) have reported existence of two gamma rhythms (slow: ~20-34 Hz and fast: ~36-66 Hz) in visual cortex, elicited by Cartesian gratings. Age-related decline in power and/or frequency of these stimulus-induced gamma rhythms has been shown in cognitively healthy subjects (17,19). However, abnormalities in such stimulus-induced visual narrow-band gamma rhythms in human patients of MCI (Mild Cognitive Impairment, a preclinical stage of dementia (20)(21)(22)) or AD have not been demonstrated till date.…”

“…We addressed this question in the present double-blind case-control EEG study involving a large cohort of elderly individuals (N=247; 106 females, all aged >49 years) recruited from urban communities in Bangalore, India. These were classified as healthy (N=227; see 17), MCI (14) or AD (6) based on clinical history and Clinical Dementia Rating (CDR; 23,24) scores. We studied narrow-band gamma rhythms induced by full screen Cartesian gratings in all these participants.…”