Inter-and intra-hemispheric EEG coherence in patients with mild cognitive impairment at rest and during working memory task

Abstract

Abstract:Objective: To assess functional relationship by calculating inter-and intra-hemispheric electroencephalography (EEG) coherence at rest and during a working memory task of patients with mild cognitive impairment (MCI). Methods: The sample consisted of 69 subjects: 35 patients (n=17 males, n=18 females; 52~71 years old) and 34 normal controls (n=17 males, n=17 females; 51~63 years old). Mini-mental state examination (MMSE) of two groups revealed that the scores of MCI patients did not differ significantly from those of normal controls (P>0.05). In EEG recording, subjects were performed at rest and during working memory task. EEG signals from F3-F4, C3-C4, P3-P4, T5-T6 and O1-O2 electrode pairs are resulted from the inter-hemispheric action, and EEG signals from F3-C3, F4-C4, C3-P3, C4-P4, P3-O1, P4-O2, T5-C3, T6-C4, T5-P3 and T6-P4 electrode pairs are resulted from the intra-hemispheric action for delta (1.0~3.5 Hz), theta (4.0~7.5 Hz), alpha-1 (8.0~10.0 Hz), alpha-2 (10.5~13.0 Hz), beta-1 (13.5~18.0 Hz) and beta-2 (18.5~30.0 Hz) frequency bands. The influence of inter-and intra-hemispheric coherence on EEG activity with eyes closed was examined using fast Fourier transformation from the 16 sampled channels. Results: During working memory tasks, the inter-and intra-hemispheric EEG coherences in all bands were significantly higher in the MCI group in comparison with those in the control group (P<0.05). However, there was no significant difference in inter-and intra-hemispheric EEG coherences between two groups at rest. Conclusion: Experimental results comprise evidence that MCI patients have higher degree of functional connectivity between hemispheres and in hemispheres during working condition. It suggests that MCI may be associated with compensatory processes during working memory tasks between hemispheres and in hemispheres. Moreover, failure of normal cortical connections may exist in MCI patients.

Synchronization during an internally directed cognitive state in healthy aging and mild cognitive impairment: a MEG study

“…These findings are in agreement with many studies which employed cognitive tasks in the MCI population (Pijnenburg et al 2004;Jiang 2005;Jiang and Zheng 2006;Bajo et al 2010). In the alpha band, however, MCIs were desynchronized during the task.…”

“…By contrast, most task studies found an increased synchronization in MCIs when compared to healthy people during a cognitive task (i.e., memory task) (Pijnenburg et al 2004;Jiang 2005;Zheng et al 2007;Bajo et al 2010). For instance, Jiang and Zheng (2006) reported a higher inter-and intrahemispheric EEG coherence in MCI in a working memory task. Bajo et al (2010) found higher interhemispheric synchronization likelihood in MCI between left and right temporo-frontal sensors in most frequency bands during a short-term memory task and higher connectivity for those that later on developed dementia (Bajo et al 2012).…”

The interactive effects of physical fitness and acute aerobic exercise on electrophysiological coherence and cognitive performance in adolescents

“…Patterns of high coherence between EEG signals recorded at different scalp sites have a functional significance because they are correlated with different kinds of cognitive information processing, like memory, language, concept retrieval, and music processing (sarnthein et al 1998;Weiss et al 1999;Weiss et al 1998;Weiss and Rappelsberger 2000). Most important for the purpose of the present study is that group differences in coherence levels have been linked with levels of cognitive ability (Jiang and Zheng 2006;Deeny et al 2009). hence, changes in EEG coherence as a function of acute exercise and fitness may be an important mechanism underlying the beneficial effects of exercise on cognitive performance.…”

A comparative study of synchrony measures for the early diagnosis of Alzheimer's disease based on EEG

“…In some studies that investigate working memory tasks (Jiang, 2005a,b;Jiang & Zheng, 2006) or probable-MCI subjects , an increase of EEG synchrony was observed. This inverse effect is often interpreted as the result of a compensatory mechanism in the brain.…”