Spurious cross-frequency amplitude-amplitude coupling in nonstationary, nonlinear signals.
Recent studies of brain activities show that cross-frequency coupling (CFC) play an important role in memory and learning. Many measures have been proposed to investigate the CFC phenomenon, including the correlation between the amplitude envelopes of two brain waves at different frequencies - cross-frequency amplitude-amplitude coupling (AAC). In this short communication, we describe how nonstationary, nonlinear oscillatory signals may produce spurious cross-frequency AAC. Utilizing the empirical mode decomposition, we also propose a new method for assessment of AAC that can potentially reduce the effects of nonlinearity and nonstatonarity and, thus, help to avoid the detection of artificial AACs. We compare the performances of this new method and the traditional Fourier-based AAC method. We also discuss the strategies to identify potential spurious AACs.
Department of Electrical Engineering, National Central University, Taoyuan City 32001, Taiwan; Research Center for Adaptive Data Analysis, National Central University, Taoyuan City 32001, Taiwan; Medical Biodynamics Program, Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA.
Chien-Hung
CH
Yeh
Research Center for Adaptive Data Analysis, National Central University, Taoyuan City 32001, Taiwan; Institute of Translational and Interdisciplinary Medicine and Department of Biomedical Sciences and Engineering, National Central University, Taoyuan City 32001, Taiwan.
Men-Tzung
MT
Lo
Medical Biodynamics Program, Division of Sleep and Circadian Disorders, Brigham and Women's Hospital, 221 Longwood Avenue, Boston, MA 02115, USA; Division of Sleep Medicine, Harvard Medical School, Boston, MA 02115, USA.
Kun
K
Hu
amplitude-amplitude coupling; cross-frequency coupling; empirical mode decomposition; modulation index; phase-amplitude coupling