Spectral Power Density Analysis of Patients with Primary Progressive Aphasia Using Resting-State Electroencephalography
Primary Progressive Aphasia (PPA) is a neurodegenerative syndrome with insidious speech and language deficits that gradually worsen as the disorder progresses. Once a general diagnosis of PPA is confirmed, it is further broken down into three variants indicated by the presence or absence of specific speech and language characteristics: nonfluent/agrammatic, semantic, and logopenic. Application of non-invasive neuroimaging techniques can help to confirm diagnosis of PPA and its three variants. The application of resting-state electroencephalography (EEG) to analyze neural oscillations via spectral power density may be more accessible to patients who are otherwise unable to use traditional imaging techniques or who struggle with task-based neuroimaging. Oscillatory slowing, characterized by an increase of relative spectral power density in the low frequency delta and theta bands, along with a reduction in spectral power in the high frequency alpha and beta bands, has been observed in persons with PPA. This study examines relative power spectral density across all three variants of PPA in the delta, theta, delta-theta, alpha, beta, and low gamma frequency bands in eyes open and eyes closed resting-state conditions to see if discernible differences were observed in each variant. The results of this study were similar to findings in previous studies for the logopenic variant, with a significant increase in relative spectral power in the low frequency delta and theta bands and a significant reduction in the high frequency beta band. In contrast to other studies, we did not observe the same decrease in spectral power for the logopenic variant in the alpha band. We did not observe the same increase in spectral power for the low frequency delta and theta bands for nonfluent or semantic variant, nor did we observe a reduction of power in the high frequency bands for these two variants, as has been observed in other studies. The high frequency low gamma band, which previous studies have not studied across the three PPA variants, showed a significant increase in spectral power in semantic variant. Our results suggest that resting-state EEG may prove useful as a biomarker for early and more accurate diagnosis of PPA.