Fast gamma oscillations weaken with age in healthy elderly in human EEG

Gamma rhythms (~20-70 Hz) have been reported to be abnormal in mental disorders such as autism and schizophrenia in humans, and Alzheimer9s disease (AD) models in rodents. However, the effect of normal aging on these oscillations is not known, especially for elderly subjects (>49 years) for which AD is most prevalent. In a first large-scale (149 subjects; 61 females) electroencephalogram (EEG) study on gamma oscillations on elderly subjects (aged 50-86 years), we presented full-screen Cartesian gratings that induced two distinct gamma oscillations (slow: 20-34 Hz and fast: 36-66 Hz). Power and centre frequency significantly decreased with age only for fast but not slow gamma or alpha. This result was independent of microsaccades and pupillary reactivity to stimulus. Steady-state visual evoked potentials (SSVEPs) also reduced with age, but in more posterior regions compared to gamma. These results are crucial first steps towards using gamma/SSVEPs as biomarkers of cognitive decline in elderly.