Might Cortical Hyper-Responsiveness in Aging Contribute to Alzheimer’s Disease?

Abstract

Our goal is to understand the neural basis of functional impairment in aging and Alzheimer’s disease (AD) to be able to characterize clinically significant decline and assess therapeutic efficacy. We used frequency-tagged ERPs to word and motion stimuli to study the effects of stimulus conditions and selective attention. ERPs to word or motion increase when a task-irrelevant 2nd stimulus is added, but decrease when the task is moved to that 2nd stimulus. Spectral analyses show task effects on response power without 2nd stimulus effects. However, phase coherence shows both 2nd stimulus and task effects. Thus, power and coherence are dissociably modulated by stimulus and task effects. Task-dependent phase coherence successively declines in aging and AD. In contrast, task-dependent spectral power increases in aging, only to decrease in AD. We hypothesize that age-related declines in signal coherence, associated with increased power generation, stresses neurons and contributes to the loss of response power and the development of functional impairment in AD.

A systematic review of cognitive event-related potentials in mild cognitive impairment and Alzheimer’s disease

“…Database searches were conducted in PsycINFO and PubMed for peer-reviewed articles in the English language. MCI searches using the keywords ["ERP" OR "event-related potential"] combined with ["MCI" OR "mild cognitive impairment"] returned a combined 169 results (69 PsycINFO; 100 PubMed). To assure comprehensive coverage, all 42 studies from Gu and Zhang's review [58] were added to the initial return list, resulting in a complete initial list of 211 studies.…”

“…The majority of the 25 studies that analyzed P300 amplitude reported smaller amplitude in AD compared to HC groups [i.e., 60%; 3,4,13,42- 43,60,63,71,84,89,114,118,142,145,152], including one reporting a trend that did not reach statistical significance[42]. The remaining ten studies reported no significant difference between groups [i.e., 40%;31,47,69,[72][73]92,105,110,126,139]. These latter AD studies were notable for small sample sizes (e.g., eight per cell), age differences between groups, high AD group MMSE scores (e.g., 27/30), and/or simple tasks (i.e., 67% oddball paradigms), which may have limited power to detect group differences.…”

“…The majority reported delayed latency in AD compared to HC groups [i.e., 66%; 3,43,52,60,63,71,76,88,92,96- 97,105,110-111,118,135,139,142,145,152], two of which reported non-significant trends[52,145]. No significant differences between groups were detected in eight studies [i.e., 27%; 4,31,47,69,75,84,114,126]. Two studies in fact reported shorter P300 latency in AD compared to HC groups [i.e., 7%; 13,72], although interpreting this in context of other studies is difficult because one also reported high P300 variability in the AD group[13], and the other used an Three of five APOE studies reported delayed P300 latencies in the ɛ4+ group when using an olfactory identification task [i.e., 60% of total studies;93,95,147].…”

EEG spectral attractors identify a geometric core of resting brain activity

“…This mirrors prior findings of exaggerated alpha-gamma synchronization between nodes of the default mode network in older adults during the resting-state, associated with impaired working memory performance and interpreted as being “stuck” in default mode (Pinal et al, 2015). Enhanced synchronization and cross-parameter coupling could reflect compensatory mechanisms to sustain neural dynamics in the face of reduced signal power or complexity (Ansado et al, 2012; Jacob & Duffy, 2014; Meunier et al, 2014; Morcom & Henson, 2018; Zahodne & Reuter-Lorenz, 2019). Longitudinal studies are needed to determine whether increased synchronization precedes the loss of complexity or results from a compensatory process.…”