The nonlinear analysis may help to reveal the complex behavior of the Electroencephalogram (EEG) signal. In order to analyze the EEG in real time, we have proposed an EEG analysis model using a nonlinear oscillator with one degree of freedom and minimum required parameters. Our method identifies EEG model parameters experimentally. The purpose of this study is to examine the specific characteristic of model parameters. Validation of the method and investigation of characteristic of model parameters were conducted based on alpha frequency EEG data in both relax state and stress state. The results of the parameter identification with the time sliding window for 1 second show almost all of the identified parameters have a normal distribution spread around the average. The model outputs can closely match the complicated experimental EEG data. The results also showed that the existence of nonlinear term in the EEG analysis is crucial and the linearity parameter shows a certain tendency as the nonlinearity increases. Furthermore, the activities of EEG become linear on the mathematical model when suddenly change from the relax state to the stress state. The results indicate that our method may provide useful information in various field including the quantification of human mental or psychological state, diagnosis of brain disease such as epilepsy and design of brain machine interface.
The decrease of arousal level has led to serious accidents in driving and operation of machine. A system to accurately evaluate arousal level in real time is required to prevent such accidents. In this paper, we examined whether parameters of the mathematical model, which are determined in each time shifting window using EEG data could be used as a method to evaluate the arousal level. The modified Duffing oscillator was proposed as a mathematical model to perform simplified parameters calculation and identification. It was applied to EEG data, which is obtained by EEG acquisition experimentation in alternative repeat of relaxed and concentrated state. As a result of the parameters identification in theta band, alpha band, beta band, and 4–30 Hz band, it is shown that each parameter is repeating increase and decrease with time progress of each experiment. Especially, the relationship between the conventional arousal level and parameter B, which is the coefficient of the proportional term in the modified Duffing oscillator shows a significant correlation. It is suggested that parameter B of the modified Duffing oscillator would evaluate the arousal level. Since this evaluation method of arousal level does not require analyzing for each band, it can be used to calculate the arousal level in real time.
Focal brain cooling has recently drawn attention as a less-invasive treatment for intractable epileptic patients. The objective of this study is to investigate the dependence of brain cooling rate on epileptic discharges (EDs) suppression with experiments using four epilepsy model rat. EDs were induced by Penicillin G in anesthetized rat, and cooled to 16 °C under four different time conditions (30, 60, 100 and 200 second, respectively). The ECoG obtained from the experiments were sorted into frequency band components which have physiological significance. The results of frequency analyses confirmed that the suppression of EDs have a cooling rate dependency, and power of four frequency bands (delta, theta, alpha and beta waves) in EDs are smaller when the cooling rate is slower. Our results suggested that slower cooling on brain surface can effectively suppress EDs and rapid brain cooling is not necessarily the best way. This finding implied that there are optimum cooling condition depending on the degree of EDs or epileptic symptoms.
A Peltier element is considered as a way to enable local temperature control and also has several advantages including rapid thermal response, no vibration and compactness. Therefore, a focal cooling device using a Peltier element for treatment is expected to apply to various parts of a living body. In the design of the device ensuring both the energy efficiency and therapeutic effect, it is necessary to understand the thermoelectric conversion characteristics of the Peltier element and the thermal conductivity of the attachment in the device, which should be designed in accordance with the cooling performance and size. Therefore, the investigation using a mathematical model is believed to play an important role in such case. The purposes of this study are to clarify the characteristics of the model parameters and to investigate whether performance evaluation of the device from its characteristics is possible. Model parameters were identified experimentally using three prototypes of different sizes and cooling abilities. From the result of the parameter identification, internal resistance and thermal conductance of the Peltier device are dependent on the cooling performance. The parameters representing the thermal conductance between each attachment in the device are strongly depend on the size. However, changes of these parameters were smaller than the size ratio of the device. Our results suggest that it can provide useful information to the designer.
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