Pharmacological and model-based interpretation of neuronal dynamics transitions during sleep-waking cycle

Power spectral analysis has been applied to spontaneous single neuronal activities during the sleep-waking cycle in various regions of the cat's central nervous system. During slow-wave sleep (SWS), the spontaneous activities of many neurons had a white noise-like power-spectral density profile in a very low frequency range (0.01-1.0 Hz) whereas, during rapid-eye-movement sleep (REMS), they showed a 1/f-like spectral pattern. This spectral transition between SWS and REMS was hypothesized to depend on the influence of serotonergic and cholinergic neuronal activity which is considered to modulate various brain functions. According to both pharmacological experiments and simulation studies with a neural network model, it was concluded that the serotonergic system may have a function to eliminate slow fluctuations in neuronal activity in wide areas, from the reticulo-thalamo-neocortical to the limbic systems. Consequently, simple signal processing of spontaneous neuronal activity has elucidated an important neurophysiological fact, which may lead to a principle of the basic brain function and its mechanism.