A novel method for evaluating rapid eye movement (REM)-like oscillatory theta activity (OTA) may be a better predictor of REM-dependent behavioral effects than current methods, according to study results presented at the 2022 Annual Meeting of the American Academy of Sleep Medicine and the Sleep Research Society, held from June 4 to 8, 2022, in Charlotte, North Carolina.
Cortical theta-band activity during REM suggests an association between REM sleep and emotional processing. The current methodology for measuring theta power is to sum total power during REM sleep as measured by polysomnography (scored-REM). However, it is hypothesized that total theta conflates different theta-band sources during scored-non-REM (NREM) sleep, termed “covert REM.”
For this study, investigators at Walter Reed Army Institute of Research hypothesized that electroencephalogram (EEG) assessment targeting all-night OTA may be a more accurate biomarker of theta-dependent REM functions.
To test an EEG-based assessment of theta-dependent REM function, 2 in-laboratory studies of 42 healthy young adults were conducted evaluating conventional staging, high-frequency activity, and the novel EEG-based method. The novel method used Irregular-Resampling Auto-Spectral Analysis to remove aperiodic spectrum followed by a low-band power normalization step.
Significant separation during all sleep stages was observed between OTA (scored-REM>scored-NREM; P =.003) and total theta-band power (scored-REM<scored-NREM; P <.001). Beta-band activity correlated with OTA (r, 0.2; P <.001) but not total theta (P =.4).
OTA was observed during scored-NREM (P <.001), supporting the covert REM hypothesis. OTA was observed during 28% (range, 2%-85%) of scored-NREM epochs.
“We developed a novel automated method for measuring REM-like oscillatory-theta activity, independent of conventional sleep staging methods,” the study authors wrote. “This method was used to measure REM-like activity across all sleep stages and […] test the hypothesis that this constitutes a better predictor of REM-dependent behavioral effects than current conventions.”
Vattikuti S Balkin T, Braun A, Riedy S, Doty T, Hughes J. Oscillatory theta-band activity as a sleep stage independent measure of REM-like activity throughout sleep. Presented at SLEEP 2022; June 4-8; Charlotte, North Carolina. Abstract 94.