Understanding early dementia: EEG, MRI, SPECT and memory evaluation

Abstract

Background: An increase in the EEG upper/low α power ratio has been associated with mild cognitive impairment (MCI) due to Alzheimer's disease (AD) and to the atrophy of temporoparietal brain areas. Subjects with a higher α3/α2 frequency power ratio showed lower brain perfusion than in the low α3/α2 group. The two groups show significantly different hippocampal volumes and correlation with θ frequency activity.

Methods: Seventy-four adult subjects with MCI underwent clinical and neuropsychological evaluation, electroencephalogram (EEG) recording, and high resolution 3D magnetic resonance imaging (MRI). Twenty-seven of them underwent EEG recording and perfusion single-photon emission computed tomography (SPECT) evaluation. The α3/α2 power ratio and cortical thickness were computed for each subject. The difference in cortical thickness between the groups was estimated.

Results: In the higher upper/low α group, memory impairment was more pronounced in both the MRI group and the SPECT MCI groups. An increase in the production of θ oscillations was associated with greater interhemisperic coupling between temporal areas. It also correlated with greater cortical atrophy and lower perfusional rate in the temporoparietal cortex.

Conclusion: High EEG upper/low α power ratio was associated with cortical thinning and lower perfusion in temporoparietal areas. Moreover, both atrophy and lower perfusion rate significantly correlated with memory impairment in MCI subjects. Therefore, the increase in the EEG upper/low α frequency power ratio could be useful in identifying individuals at risk for progression to AD dementia in a clinical context.

Keywords: EEG; MRI; Memory; Prodromal Alzheimer’s disease; SPECT.

Figure 1

The brain regions with higher regional cortical thickness in MCI with a high α3/α2 ratio as compared to MCI with low α3/α2 ratio (p < 0.01 uncorrected) are represented in red. The color-coding for p values is on a logarithmic scale. Results are presented on the pial cortical surface. Dark gray regions represent sulci and light gray regions represent gyri.

Figure 2

The brain regions with higher regional cortical thickness in MCI subjects with a high α3/α2 ratio as compared to MCI subjects with a middle α3/α2 ratio are represented in red (p < 0.01 uncorrected). The color-coding for p values is on a logarithmic scale. Results are presented on the pial cortical surface. Dark gray regions represent sulci and light gray regions represent gyri.

Figure 3

EEG coherence statistical results. A. frontoparietal interhemispheric coherence, B. frontotemporal interhemispheric coherence, C. temporoparietal interhemispheric coherence.

Figure 4

SPECT visual rating. The output shows a SPECT visual inspection of glucose uptake metabolism: the white ellipses denote an area of mild-to-moderate hypometabolism in one of the 14 at low risk and in one of the 13 at high risk MCI patients with respect to one of the 17 enrolled controls (unlabeled on the left side).