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.
Highlights
Aging is the #1 risk factor for Alzheimer’s disease (AD), mechanisms linking those conditions have long remained obscure [1]
We have examined these hypotheses by assaying competitive attentional control of the dorsal and ventral extrastriate cortical visual systems in aging and AD
We have explored the attentional control of visual motion and object processing in monkeys and humans
Summary
Aging is the #1 risk factor for AD, mechanisms linking those conditions have long remained obscure [1]. We consider that age-related cortical hyper-responsiveness may reflect a variety of contributing factors: local disinhibition from intra-cortical (e.g., loss of GABAergic neurons) or cortico-cortical (e.g., fronto-posterior de-afferentation) [11,12,13], and over-activation as a consequence of, or in compensation for, signal degradation [14,15]. We have examined these hypotheses by assaying competitive attentional control of the dorsal and ventral extrastriate cortical visual systems in aging and AD. These parallel systems partition signals for object and motion processing [16,17]. The relative activity of these pathways is shaped by selective attention’s biasing their competitive interactions [18,19,20] to implement behavioral priorities and optimize function [21,22,23]
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