Nonlinear dynamics of evoked neuromagnetic responses signifies potential defensive mechanisms against photosensitivity

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Bhattacharya, Joydeep; Watanabe, Katsumi and Shimojo, Shinsuke. 2004. Nonlinear dynamics of evoked neuromagnetic responses signifies potential defensive mechanisms against photosensitivity. International Journal of Bifurcation and Chaos [in Applied Sciences and Engineering], 14(8), pp. 2701-2720. ISSN 02181274 [Article]

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Official URL: http://dx.doi.org/10.1142/S0218127404010850

Abstract or Description

We investigated the dynamical characteristics of neuromagnetic responses by recording magnetoencephalographic (MEG) signals to equiluminant flickering stimulus of different color combinations from a group of control subjects, and from a patient with photosensitive epilepsy. By wavelet based time-frequency analysis, we showed that two distinct neuromagentic responses corresponding to stimulus frequency and its time delayed first harmonic were found in control subjects, whereas no harmonic response was obtained for the patient. We applied a battery of methods (sample entropy measuring signal complexity and index of smoothness measuring determinism) based on nonlinear dynamical system theory in conjunction with bootstrapping surrogate analysis. The results suggested that a significant nonlinear structure was evident in the MEG signals for control subjects, whereas nonlinearity was not detected for the patient. In addition, the couplings between distant cortical regions were found to be greater for control subjects. The important role of combinational chromatic sensitivity in sustained cortical excitation was also confirmed. These findings lead to the hypothesis that the healthy human brain is most likely equipped with significantly nonlinear neuronal processing reflecting an inherent mechanism defending against hyper-excitation to chromatic flickering stimulus, and such nonlinear mechanism is likely to be impaired for a patient with photosensitive epilepsy.

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Article

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https://doi.org/10.1142/S0218127404010850