Healthy and Pathological Brain Aging: From the Perspective of Oscillations, Functional Connectivity, and Signal Complexity

Abstract

Healthy aging is associated with impairment in cognitive information processing. Several neuroimaging methods such as functional magnetic resonance imaging, positron emission tomography and near-infrared spectroscopy have been used to explore healthy and pathological aging by relying on hemodynamic or metabolic changes that occur in response to brain activity. Since electroencephalography (EEG) and magnetoencephalography (MEG) are able to measure neural activity directly with a high temporal resolution of milliseconds, these neurophysiological techniques are particularly important to investigate the dynamics of brain activity underlying neurocognitive aging. It is well known that age is a major risk factor for Alzheimer’s disease (AD), and that synaptic dysfunction represents an early sign of this disease associated with hallmark neuropathological findings. However, the neurophysiological mechanisms underlying AD are not fully elucidated. This review addresses healthy and pathological brain aging from a neurophysiological perspective, focusing on oscillatory activity changes during the resting state, event-related potentials and stimulus-induced oscillatory responses during cognitive or motor tasks, functional connectivity between brain regions, and changes in signal complexity. We also highlight the accumulating evidence on age-related EEG/MEG changes and biological markers of brain neurodegeneration, including genetic factors, structural abnormalities on magnetic resonance images, and the biochemical changes associated with Aβ deposition and tau pathology.

Age-Dependent Effect of Transcranial Alternating Current Stimulation on Motor Skill Consolidation

“…Aging also affects alpha oscillatory activity in other brain regions. With regard to the posterior alpha rhythm (8-13 Hz), there was a marked reduction in amplitude, slowing of spontaneous oscillation, and declined reactivity (eye-opening) which correlated with global cognitive performance in the elderly (Babiloni et al, 2006;Ishii et al, 2017;Knyazeva et al, 2018). Older adults also showed reduced connectivity in the upper alpha band compared to young adults (Kikuchi et al, 2000;Vysata et al, 2014;Scally et al, 2018).…”

“…Older adults also showed reduced connectivity in the upper alpha band compared to young adults (Kikuchi et al, 2000;Vysata et al, 2014;Scally et al, 2018). Other changes due to aging include a significant alpha increase in frontal regions, mainly over the prefrontal cortex (PFC), which has also been observed in early Alzheimer's disease patients (Kolev et al, 2002;Ishii et al, 2017). The shift of alpha from posterior to frontal regions has been associated with a compensatory mechanism.…”

“…Older adults need to activate the PFC even to accomplish very easy tasks, whereas younger adults do not have to draw on this cortical resource (Mattay et al, 2002;Berchicci et al, 2012). The evidence so far, thus suggests a causal link between impaired alpha activity and cognitive and motor impairment in healthy aging, as well as a link to pathological conditions such as Alzheimer's disease (Ishii et al, 2017;Koelewijn et al, 2017). It is therefore timely to develop interventions that can modulate the alpha rhythm in the elderly.…”

Genetic Association Between Alzheimer’s Disease Risk Variant of the PICALM Gene and EEG Functional Connectivity in Non-demented Adults

“…In MCI and prodromal AD, alpha disconnection in brain networks is related to progressive cognitive impairment. The alterations in connectivity may be influenced by the accumulation of amyloid and tau deposition, synaptic disruption and impaired axonal integrity (Canuet et al, 2015;Ishii et al, 2017).…”

Standard multiscale entropy reflects neural dynamics at mismatched temporal scales: What’s signal irregularity got to do with it?

“…In line with this prediction, entropy consistently decreased with 972 more stereotypic spectral events, suggesting that narrowband entropy can indeed reflect the (ir-973 )regularity of rhythmic episodes. Posterior-occipital decreases in alpha power and frequency 974 with age are considered fundamental features of age-comparative studies (Ishii et al, 2017) that 975 may in part reflect structural shifts in the generating networks (Knyazeva, Barzegaran, 976…”