Delay of cognitive gamma responses in Alzheimer's disease.

Erol Başar,Görsev G Yener,Bahar Güntekin,Derya Durusu Emek-Savaş

doi:10.1016/j.nicl.2016.01.015

Erol Başar, Görsev G Yener + Show 2 more

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https://doi.org/10.1016/j.nicl.2016.01.015

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Abstract

Event-related oscillations (EROs) reflect cognitive brain dynamics, while sensory-evoked oscillations (SEOs) reflect sensory activities. Previous reports from our lab have shown that those with Alzheimer's disease (AD) or mild cognitive impairment (MCI) have decreased activity and/or coherence in delta, theta, alpha and beta cognitive responses. In the current study, we investigated gamma responses in visual SEO and ERO in 15 patients with AD and in 15 age-, gender- and education-matched healthy controls. The following parameters were analyzed over the parietal-occipital regions in both groups: (i) latency of the maximum gamma response over a 0–800 ms time window; (ii) the maximum peak-to-peak amplitudes for each participant's averaged SEO and ERO gamma responses in 3 frequency ranges (25–30, 30–35, 40–48 Hz); and (iii) the maximum peak-to-peak amplitudes for each participant's averaged SEO and ERO gamma responses over a 0–800 ms time block containing four divided time windows (0–200, 200–400, 400–600, and 600–800 ms). There were main group effects in terms of both latency and peak-to-peak amplitudes of gamma ERO. However, peak-to-peak gamma ERO amplitude differences became noticeable only when the time block was divided into four time windows. SEO amplitudes in the 25–30 Hz frequency range of the 0–200 ms time window over the left hemisphere were greater in the healthy controls than in those with AD. Gamma target ERO latency was delayed up to 138 ms in AD patients when compared to healthy controls. This finding may be an effect of lagged neural signaling in cognitive circuits, which is reflected by the delayed gamma responses in those with AD. Based on the results of this study, we propose that gamma responses should be examined in a more detailed fashion using multiple frequency and time windows.

Highlights

Alzheimer's disease (AD) is the most common dementing illness
We explored event-related oscillations (EROs), sensory-evoked oscillations (SEOs), and the evoked or event-related coherence of AD/mild cognitive impairment (MCI) patients using visual and auditory sensory modalities (Yener et al, 2008, 2009, 2012; Güntekin et al, 2008; Basar et al, 2010; Yener and Başar, 2010)
The repeated measures ANOVA analysis of “maximum peak-to-peak gamma amplitudes for three different gamma frequency ranges over a 0–800 ms time window” included 2-level GROUP (AD patients and healthy controls) as between-subject factors, and frequency range (FR [3 levels] = 25–30 Hz, 30–35, 40–48 Hz), anterior–posterior

Summary

Introduction

Alzheimer's disease (AD) is the most common dementing illness. In the majority of cases, mild cognitive impairment (MCI) is considered to be prodromal AD (Petersen et al, 2001; Rasquin et al, 2005; Alexopoulos et al, 2006). The full potential of electrophysiological methods for use in predicting (Cichocki et al, 2005; Babiloni et al, 2006a; Rossini et al, 2006), diagnosing (Yener et al, 1996; Polich and Herbst, 2000; Jeong, 2004; Babiloni et al, 2006b; Karrasch et al, 2006), and monitoring treatment or progress (Jelic et al, 2000; Dauwels et al, 2010) in AD/MCI patients has not been fully examined in routine clinical practice. Brain oscillatory responses can be used for the non-invasive analysis of local neuronal synchronization, cortico-cortical connectivity, and coherence of oscillations (Rossini et al, 2007). Cognitive stimuli can elicit event-related oscillations (EROs), which is a powerful technique with high temporal resolution. ERO has been described as a useful tool for detecting subtle abnormalities of cognitive processes (Basar, 1980, 2004)

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