Abstract
In most mammals, the sleep-wake cycle is constituted by three behavioral states: wakefulness (W), non-REM (NREM) sleep, and REM sleep. These states are associated with drastic changes in cognitive capacities, mostly determined by the function of the thalamo-cortical system. The intra-cranial electroencephalogram or electocorticogram (ECoG), is an important tool for measuring the changes in the thalamo-cortical activity during W and sleep. In the present study we analyzed broad-band ECoG recordings of the rat by means of a time-series complexity measure that is easy to implement and robust to noise: the Permutation Entropy (PeEn). We found that PeEn is maximal during W and decreases during sleep. These results bring to light the different thalamo-cortical dynamics emerging during sleep-wake states, which are associated with the well-known spectral changes that occur when passing from W to sleep. Moreover, the PeEn analysis allows us to determine behavioral states independently of the electrodes’ cortical location, which points to an underlying global pattern in the signal that differs among the cycle states that is missed by classical methods. Consequently, our data suggest that PeEn analysis of a single EEG channel could allow for cheap, easy, and efficient sleep monitoring.
Highlights
In most mammals, the sleep-wake cycle is constituted by three behavioral states: wakefulness (W), non-rapid eye movement (REM) (NREM) sleep, and REM sleep
Electrode locations are shown on the left panel and the intra-cranial polysomnographic recordings for W, NREM, and REM sleep states are shown on the right panels, which have been distinguished by means of the standard sleep scoring criteria
Maximal Permutation Entropy (PeEn) values were achieved during W, PeEN values decreased during NREM sleep and reached minimum values during REM sleep
Summary
The sleep-wake cycle is constituted by three behavioral states: wakefulness (W), non-REM (NREM) sleep, and REM sleep These states are associated with drastic changes in cognitive capacities, mostly determined by the function of the thalamo-cortical system. Due to the complex nature of the standard EEG and ECoG signals, traditional methods employed in neuroscience have divided the complex spectrum of the signal into frequency bands[3,5,6,7,8,9], and analyzed its changes during different cognitive functions[4,7], and sleep states[5,6,8] These methods only describe particular characteristics of the recorded signals and do not account for the complex nature of the cortical electric potentials. In order to study the thalamo-cortical function during W and sleep, PeEn is a practical and reliable method, where results can be understood from primary principles, and can be related to the signal characteristics
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