* Corresponding author:
sray@iisc.ac.in
Keywords: EEG, Gamma oscillations, healthy aging, cluster shrinkage,
functional connectivity, Alzheimer’s Disease
Number of figures: 6
Declaration of interests: The authors declare no competing financial
interests.
Funding disclosure and Acknowledgements: This work was supported by Tata
Trusts Grant, Wellcome Trust/DBT India Alliance (Senior fellowship
IA/S/18/2/504003 to SR), and DBT-IISc Partnership Programme.
Abstract
Functional connectivity (FC) indicates the interdependencies between
brain signals recorded from spatially distinct locations in different
frequency bands, which is modulated by cognitive tasks and is known to
change with aging and cognitive disorders. Recently, the power of
narrow-band gamma oscillations induced by visual gratings has been shown
to reduce with both healthy aging and in subjects with mild cognitive
impairment (MCI). However, the impact of aging/MCI on stimulus-induced
gamma FC has not been well studied. We recorded electroencephalogram
(EEG) from a large cohort (N=229) of elderly subjects (>49
years) while they viewed large cartesian gratings to induce gamma
oscillations and studied changes in alpha and gamma FC with healthy
aging (N=218) and MCI (N=11). Surprisingly, we found that aging and
disease changed power and FC in different ways. With healthy aging,
alpha power did not change but FC decreased significantly. MCI reduced
gamma but not alpha FC significantly compared with age and gender
matched controls, even when power was matched between the two groups.
Overall, our results show distinct effects of aging and disease on EEG
power and FC, suggesting different mechanisms underlying aging and
cognitive disorders.
Key points
1. First large-scale EEG study on stimulus-induced narrowband gamma FC
in elderly.
2. Cognitively healthy and MCI patients show distinct power and induced
FC changes.
3. Slow gamma FC decreased with MCI, while alpha FC also reduced with
healthy aging.