Search

We developed a phase dynamics model of human circadian rhythms that allows non-photic entrainment. Characteristically, our model can simulate the interaction between the melatonin and the sleep-wake rhythms, which owes mainly to the discontinuity in couplings between oscillators in the model. On the other hand, we studied the bifurcation structure of the two process model based on a constructed circle map of the model. This circle map was characterized by its discontinuity. Here, the same circle map was constructed for our model, which was shown to have similar discontinuity to the two process model. Considering the discontinuity shared by the different models, this property may be an essential property in the human circadian rhythms., この論文は国立情報学研究所の電子図書館事業により電子化されました。, 研究会報告

Some patients with amputations are known to still experience presence of the amputated limb (phantom limb). Phantom limb is found to be accompanied by reorganizations of somatotopic representations at cortical and subcortical levels due to deafferentation, which also discloses presence of body schema, i.e., integrated image of body. In addition, phantom limb is often recognized with painful sensation, i.e., phantom pain, which is suggested to be caused by abnormally high activations in thalamocortical neurons in the deafferentated area. In this paper, simulations using a self-organizing neural network model were performed to clarify contribution of axonal sprouting and body schema to reorganization of cortical representation, and to explore a possible mechanism underlying abnormally high thalamocortical activation. The results showed that axonal sprouting could cause reorganization of cortical mapping with an aid of facilitatory inputs referring to the conserved body schema even after deafferentation. In addition, removing thalamic recurrent inhibitions was shown to induce high and sustained activations in thalamocortical neurons in the deafferentated area. Consequently, this study suggested that discordance between the recognized cortical representation and physiological process referring to the body schema could give rise to phantom pain. Phantom pain is a clue disclosing how body schema is constructed and maintained, which might be an important subject also for robotics dealing with an artificial body.

EEG activities in the higher frequency range rather than the conventionally used was hypothesized to be more directly related to neurogenic activities which are expected to construct EEG activities. According to this hypothesis, EEG activities up to 90 Hz were measured and analyzed during REM sleep. REM sleep is considered to be only a physiological state which allows one to measure the high frequency EEG activities without contamination of EMG due to muscle atonia except for twitches. The study found that the rhythmic activities with different frequencies randomly appeared one after another in the frequency range up to at least 90 Hz. This result suggests that the rivalry among small neural assemblies activated synchronously is realized during REM sleep, which might be understood within our hypothesized framework of disinhibition and activation associated with REM sleep. In addition, the extremely wide bandwidth of 500 Hz analyzed here disclosed the phasic potentials related to the rapid eye movements which had the consistent topographic pattern, i.e., frontal positive and occipital negative, which suggests the dipole located deep in the brain. This phasic event may be related to a neurogenic potential generating ponto-geniculo-occipital (PGO) wave observed in cats during REM sleep. Therefore, our finding potentially discloses novel aspects of human neurophysiology.

We developed a phase dynamics model of human circadian rhythms that allows non-photic entrainment. Characteristically, our model can simulate the interaction between the melatonin and the sleep-wake rhythms, which owes mainly to the discontinuity in couplings between oscillators in the model. On the other hand, we studied the bifurcation structure of the two process model based on a constructed circle map of the model. This circle map was characterized by its discontinuity. Here, the same circle map was constructed for our model, which was shown to have similar discontinuity to the two process model. Considering the discontinuity shared by the different models, this property may be an essential property in the human circadian rhythms.