TY - JOUR
T1 - Nonlinear dynamics of evoked neuromagnetic responses signifies potential defensive mechanisms against photosensitivity
AU - Bhattacharya, Joydeep
AU - Watanabe, Katsumi
AU - Shimojo, Shinsuke
PY - 2004/8
Y1 - 2004/8
N2 - 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 nickering stimulus, and such nonlinear mechanism is likely to be impaired for a patient with photosensitive epilepsy.
AB - 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 nickering stimulus, and such nonlinear mechanism is likely to be impaired for a patient with photosensitive epilepsy.
KW - Chromatic flicker
KW - Complexity
KW - Determinism
KW - Interdependency
KW - Magnetoencephalography (MEG)
KW - Nonlinearity
KW - Photosensitive epilepsy
KW - Surrogate analysis
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U2 - 10.1142/S0218127404010850
DO - 10.1142/S0218127404010850
M3 - Article
AN - SCOPUS:4944266997
VL - 14
SP - 2701
EP - 2720
JO - International Journal of Bifurcation and Chaos
JF - International Journal of Bifurcation and Chaos
SN - 0218-1274
IS - 8
ER -