Biological and Physiological Engineering Study on Global Regulatory Mechanisms of The Brain as A Complex System

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As a representative of a complex system, global regulatory mechanisms of the brain are investigated from the biological and physiological engineering point of view. The research results are summarizedas follows.1.Dynamics tratnsitions of neuronal activities during sleep cycles are studied in the lateral geniculate nucleus (LGN) and the cortical areas 18 and 6. The LGN neurons characteristically show bursting activities, which are confirmed to exhibit the neuronal dynamics transition from the white power spectral density (PSD) (slow wave sleep : SWS) to the 1/f PSD (rapid eye movement sleep : REM). The cortical neurons also exhibit the same dynamics transition as the neurons studied so far. These results support our hypothesis that neurons in the processing systems of the brain commonly exhibit the concerned dynamics transitions during sleep cycles.2.The length of the column, the compositions of medium, and the oxidation-reduction potential of the high precision liquid chromatography ar … More e optimized to carry out a microdialysis of serotonin concentration, a neurotransmitter of the regulatory system in the brain, which enables us to study the relationship between the serotonin concentration and the neuronal dynamics. As a result, concentration can be measured down to an order of fmol. By this novel method, sleep-wake-dependent variations of the serotonin concentration are measured in LGN (wake>SWS>REM).3.Mechanisms underlying the neuronal dynamics transition are investigated based on the neural network model, which shows that the balance between the inputs from the neurons within the network and those from the external neurons is essential for this phenomenon. That is, for the 1/f fluctuations the internal inputs are required to dominate the external, and the opposite relation should be satisfied for the random activities exhibiting the white PSD.This suggests that the regulatory system exerts diverse effects on the concerned dynamics transition. In addition, the metastability of the neural network relates to REM sleep might be a physiological substrate of dreaming, which provides a novel information for understanding the relationship between dreaming and higher-order brain functions. Less