A Study Of EEG Power And Coherence During A Working Memory Task In The Patients With Mild Cognitive Impairment

Mild cognitive impairment (MCI) is an operational diagnostic term developed to describe the earliest, preclinical stages of AD. It refers to objective cognitive deficits which exceed normal physiological aging processes, but do not fulfill the criteria for dementia. Subjects with MCI are considered to be at high risk of developing AD. Research in MCI has focused on defining methods for the earliest detection of dementia. The inclusion of electroencephalography (EEG) examinations in the diagnostic work-up is encouraged by its availability and noninvasiveness.ObjectiveTo study the feature of memory-related Electroencephalography (EEG) power and neuropsychology in patients with mild cognitive impairment (MCI) and the relationship between them.To describe alterations of memory-related EEG interhemispheric and intrehemispheric coherence in patients with MCI and to verify whether or not the patient with MCI has any breakdown of neural network communication.MethodsMini-mental state examination (MMSE) , Activities of Daily Living Scale (ADL) and Clinical Dementia Rating (CDR) were administered to 13 patients with MCI and 13 controls. Then EEGs were recorded at rest as well as during working memory task with three levels of working memory load. The EEG powers was computed over 10 channels ( right and left frontal, central, parietal, temporal and occipital) for delta (1-3.5 Hz) , theta (4-7.5 Hz), alphal (8-10 Hz), alpha2 (10.5-13 Hz), betal(13.5-18 Hz) and beta2 (18.5-30 Hz) frequency bands. Interhemispheric EEG coherence for 5 homologous electrode pairs of right and left frontal ( F3-F4), central (C3-C4) , parietal (P3-P4), temporal (T5-T6) and occipital (01-02) was computed at rest and during working memory task. And EEG intrehemispheric coherence at four conditions was measured for 10 electrode pairs of left and right fronto-central (F3-C3, F4-C4), centro-parietal (C3-P3, C4-P4), parieto-occipital (P3-O1, P4-O2), temporo-central (T5-C3, T6-C4), temporo-parietal (T5-P3, T6-P4) .ResultsAll of the EEG powers of MCI were higher than controls at resting EEG or during working memory task. During working memory task, while the delta band and theta band powers were significantly increased, the alphal band power was significantly decreased. In the MCI group there were significant negative correlations between MMSE score and powers, and responded to WM demands the electrodes were becoming more and more.Compared with the normal controls, the MCI patients had higher coherences in both the intra- and interhemispheric at resting EEG or during working memory task. Both the intra- and interhemispheric coherences during WM1 task were significantlylower than during other three conditions. In every frequency band, the temporo-central (T5-C3, T6-C4), temporo-parietal (T5-P3, T6-P4) coherence was significantly decreased compared with fronto-central(F3-C3, F4-C4), centro-parietal (C3-P3, C4-P4), parieto-occipital (P3-O1, P4-O2) coherence.Conclusions1. It could be postulated that the delta band , theta band and alphal band are to be associated with the working memory functions.2. 2. The results suggested that MCI may be associated with compensatory processes.3. 3. The results support the hypothesis that there was a breakdown of the functional link between temporal with other cortical sites in the MCI patients, and the deficits of cortical connections are involved in nomal elderly control.