Understanding the dynamics of brain activity manifested in the electroencephalogram (EEG), local-field potentials (LFP) and neuronal spiking is essential for explaining their underlying mechanisms and physiological significance. Much has been learned about sleep regulation using conventional EEG power spectrum, coherence and period-amplitude analyses, which focus primarily on frequency and amplitude characteristics of the signals and on their spatio-temporal synchronicity. However, little is known about the effects of ongoing brain state or preceding sleep-wake history on the nonlinear dynamics of brain activity. Recent advances in developing novel mathematical approaches for investigating temporal structure of brain activity based on such measures, as Lempel-Ziv complexity (LZC) can provide insights that go beyond those obtained with conventional techniques of signal analysis. Here we used extensive data sets obtained in spontaneously awake and sleeping adult male laboratory rats, as well as during and after sleep deprivation, to perform a detailed analysis of cortical local field potential (LFP) and neuronal activity with LZC approach. We found that activated brain states - waking and rapid-eye movement (REM) sleep are characterized by higher LZC as compared to non-rapid-eye movement (NREM) sleep. Notably, LZC values derived from the LFP were especially low during early NREM sleep after sleep deprivation, and towards the middle of individual NREM sleep episodes. We conclude that LZC is an important and yet largely unexplored measure with a high potential for investigating neurophysiologic mechanisms of brain activity in health and disease.
- Lempel-Ziv Complexity
- local field potentials
- neuronal activity
- Copyright © 2014, Journal of Neurophysiology