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P4‐103: Decrease in event‐related EEG coherence in Alzheimer's patients during an episodic memory paradigm
Author(s) -
Morison Gordon,
Kilborn Kerry,
Tieges Zoe
Publication year - 2011
Publication title -
alzheimer's and dementia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.713
H-Index - 118
eISSN - 1552-5279
pISSN - 1552-5260
DOI - 10.1016/j.jalz.2011.05.2124
Subject(s) - electroencephalography , neuroscience , episodic memory , audiology , psychology , hippocampal formation , sensory memory , stimulus (psychology) , cognitive psychology , cognition , medicine , mismatch negativity
Background: The EEG of Alzheimer’s disease (AD)patients is characterized by a slowing of the power spectrum and a loss offunctional connectivity or coherence. Most studies have examined EEG coherencein resting-state conditions, and have identified deficits in interand intra-hemisphericconnectivity, leading to suggestions that AD may be characterized as adisconnection syndrome involving reduced interactions between widely separatedbrain regions. Here we investigate the topographic characteristics of EEGcoherence in AD patients during execution of a cross-modal episodic memoryparadigm.Methods:We employed a new/old taskin which stimulus pairs were composed of a visual image (e.g., a train)presented simultaneously with an auditory word (e.g,"tunnel"). EEGwas measured continuously from 128 channels. The task was designed toelicit brain and behavioral responses that rely on hippocampal function in twoways. First, the hippocampus is involved in encoding short-term episodicmemories linking the associated stimulus pairs. Second, the hippocampus isinvolved in the processing and integration of cross-modal sensory input (i.e.,visual and auditory). The memory task was completed by 63 non-medicated, newlydiagnosed AD patients and 73 healthy age-matched controls. Results: Coherence values were normalized usingFisher’s Z transformation and computed for five frequency bands:delta (1-3.5Hz), theta (4-7.5Hz), lower alpha (8-10Hz), upper alpha (10.5-13Hz)and beta (13.5-20Hz). Coherence values for frontal-parietal, frontal-occipital,and frontal-temporal electrode pairs over both hemispheres were analyzed. Event-related coherence in delta,theta and alpha (but not beta) ranges was significantly reduced in AD patients compared with controls (p < .006). For frequencies up until theta, this lossof intrahemispheric interactions was most pronounced for frontoparietalelectrode pairs (p< .002), whereas the loss of coherence for higherfrequencies was mainly seen for fronto-occipital electrode pairs (p < .005). These effects were similar over both hemispheres. Conclusions: Loss of functional connectivity inAD during memory activation was evidenced by specific changes in long range interactionsin the beta, theta, alpha1, alpha2 and beta bands. The functional disconnectionobserved here was intrahemispheric, and present in both hemispheres. These findings suggest that highly interconnected neural networks that servelong-range communication within hemispheres may be at risk in AD.