Objective: This cross-sectional study investigated the relationship between depression and sigma absolute spectral power (9-15 Hz) in the frequency range of sleep spindles during non-rapid eye movement (non-REM) sleep stages 2 and 3 (N2 and N3), in Parkinson’s disease (PD).

Background: Patients with PD often experience sleep disorders and depression, and these conditions are connected in a bidirectional manner(1). As PD affects circuitry in the thalamocortical system(2) where spindles are generated(3), we investigated whether sigma absolute spectral power correlates with depression in PD.

Method: Polysomnography (PSG) and the Beck Depression Inventory (BDI) were collected on 54 participants with PD. Using a frequency resolution of 1 Hz, we calculated absolute spectral power in the sigma range (9-15 Hz) in PSG-derived sleep EEG after rejecting movement and electrical artifacts (11.9% N2 and 4.9% N3 30-second epochs) in central leads (C3 and C4). Pearson correlation coefficients were used to assess the relationship between BDI and sigma absolute spectral power during N2 and N3. As an exploratory analysis, we examined the correlation between BDI and sigma absolute spectral power separately for N2 and N3.

Results: The 54 participants were 65% male; 96% Caucasian; 65.9 +/- 7.2 years of age (mean +/- SD); duration of disease: 5 (0.16-20), median (range) and levodopa equivalent dose: 600 (0-4622.2). There was a significant correlation between sigma absolute spectral power and BDI (r=0.32, p=0.02). This relationship remained significant after adjusting for disease duration and sex, which were the only two significant demographic predictor variables for sigma absolute spectral power. Exploratory analysis showed significant correlations between BDI and sigma power in both N2 and N3 (r=0.31, p=0.024, and r=0.33, p=0.017, respectively).

Conclusion: PD patients with higher sigma absolute spectral power during N2 and N3 have higher depression scores. Therefore, sigma spectral power may serve as an important marker for assessing depression in patients with PD. In addition, a better understanding of this electrophysiological rhythm of sleep may facilitate the development of novel therapeutic options for treating depression or monitoring its response to treatment.

References: 1.    Kay DB, Tanner JJ, Bowers D. Sleep disturbances and depression severity in patients with Parkinson’s disease. Brain Behav. 2018 Jun;8(6):e00967.
2.    Wichmann T. Changing views of the pathophysiology of Parkinsonism. Mov Disord. 2019 Aug;34(8):1130–43.
3.    Fernandez LMJ, Lüthi A. Sleep spindles: mechanisms and functions. Physiol Rev. 2020 Apr 1;100(2):805–68.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/sigma-absolute-spectral-power-is-associated-with-depression-in-parkinsons-disease/