The Contribution of EEG to the Diagnosis of Dementia

Abstract

Changes induced by cerebrovascular damage (CVD) and amigdalo-hippocampal atrophy (AHC) on brain rhythmicity as revelaled by scalp electroencephalography (EEG) were evaluated in a cohort of subjects with mild cognitive impairment (MCI) in order to detect different EEG patterns due to the vascular or degenerative impairment. All subjects underwent EEG recording and magnetic resonance imaging (MRI). EEGs were recorded at rest. Relative power was separately computed for delta, theta, alpha1, alpha2, and alpha 3 frequency bands. Increased delta power and decreased alpha2 power were associated with the load of cerebrovascular damage (CVD). Moreover, the theta/alpha 1 ratio could be a reliable index for the estimation of the individual extent of CV damage. No association of vascular damage was observed with alpha3 power. On the other side, moderate hippocampal atrophy was related to an increase of alpha2 and alpha3 frequency power ratio. Our results show that different EEG markers are associated to vascular dementia and Alzheimer's disease (AD). EEG markers could be expression of different global network pathological changes, helping in differentiation of prodromal AD from vascular demented patients. MCI stated that EEG markers could have a prospective value in differential diagnosis between vascular and degenerative MCI. Keywords EEG, Dementia, Brain Rhythms Shared Procedures EEG RecordingsAll recordings were obtained in the morning with subjects resting comfortably. Vigilance was continuously monitored in order to avoid drowsiness.The EEG activity was recorded continuously from 19 sites by using electrodes set in an elastic cap (Electro-Cap International, Inc.) and positioned according to the 10 -20 International system (Fp1, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, O2). The ground electrode was placed in front of Fz. The left and right mastoids served as reference for all electrodes. The recordings were used off-line to re-reference the scalp recordings to the common average. Data were recorded with a band-pass filter of 0.3 -70 Hz, and digitized at a sampling rate of 250 Hz (BrainAmp, BrainProducts, Germany). Electrodes-skin impedance was set below 5 kW. Horizontal and vertical eye movements were detected by recording the electrooculogram (EOG). The recording lasted 5 minutes, with subjects with closed eyes. Longer recordings would have reduced the variability of the data, but they would also have increased the possibility of slowing of EEG oscillations due to reduced vigilance and arousal. EEG data were then analyzed and fragmented off-line in consecutive epochs of 2 seconds, with a frequency resolution of 0.5 Hz. The average number of epochs analyzed was 140 ranging from 130 to 150. The EEG epochs with ocular, muscular and other types of artifacts were discarded.

Resting state EEG biomarkers of cognitive decline associated with Alzheimer’s disease and mild cognitive impairment

“…The correlation between PDDM95 and MMSE was highest at channels F7 (r(24) = -.77, p = 3.5x10 -6 )and lowest at channel O2 (r(24) = -.66, p = 2.7x10 -4 ). These results are consistent with previous reports [30,36,64,65] reporting the correlation between EEG measures and MMSE scores in AD. However, there was no significant correlation between EEG measures and MMSE scores in the MCI group.…”

Association between gait speed deterioration and EEG abnormalities

“…Several authors have reported increments in the EEG spectral power at slower frequencies (delta and theta) and a decrease in alpha band energy, especially in alpha-1, in individuals with Alzheimer's disease (AD), vascular dementia and mild cognitive impairment (MCI) [21,[34][35][36]. In particular, higher power in the theta band over the temporal lobe compared to agematched control has been proposed as a marker of Alzheimer's dementia [37].…”

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“…Several authors have reported increments in the EEG spectral power at slower frequencies (delta and theta) and a decrease in alpha band energy, especially in alpha-1, in individuals with Alzheimer's disease (AD), vascular dementia and mild cognitive impairment (MCI) [21,[34][35][36]. In particular, higher power in the theta band over the temporal lobe compared to agematched control has been proposed as a marker of Alzheimer's dementia [37].…”