Quantitative analysis of EEG signals: Time-frequency methods and ...

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3 2 3 3 3 3.2 Hz 3.6 Hz 4.0 Hz 4.4 Hz 2 2 2 1 1 1 1 0 0 0 0 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 3 2 3 3 4.8 Hz 5.2 Hz 5.6 Hz 6.0 Hz 2 2 2 3 1 1 1 1 0 0 0 0 49 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 0 20 40 60 80 3 6.4 Hz 2 1 0 0 20 40 60 80 Figure 17: Wavelet packets for the scale level B4.
4.4.3 Discussion The high time-frequency resolution achieved with Wavelet Packets allowed a very detailed study of the time evolution of the frequency peaks during the seizure. In fact, it was possible to establish that the high amplitude peaks of about 3 ; 4Hz,characteristic of the clonic activity, were generated in higher frequencies. This result is in agreement with the dynamic described with the Gabor Transform. In this case, with the RIR (see sec. x3.4) I showed how during the seizure the relevant brain activity was dominated by alpha and theta bands, until the ending of the seizure, when delta activity dominated again. Then, it is reasonable to conjecture that the violent clonic contractions characteristic of the clonic phase of the Grand Mal seizures are the response to brain oscillations generated in higher frequencies, but owing to the fact that the muscles can not contract so fast, the muscle activity is limited to a tonic contraction until the oscillations become slower and the muscles are capable to oscillate in resonance with them. It is interesting to note that the frequency behavior described is in agreement with simulations of thalamic slices performed by Wang and coworkers (Wang et al., 1995 Golomb et al., 1996), who observed a slowing from 10Hz to 4Hz in their simulations after the suppression of GABA A inhibitors. This result is also in agreement with in vitro experimental results of Bal et al. (1995a,b). These experiments suggest that it would be very interesting to investigate if the \slowing" of the frequencies observed during the seizures can be related with a variation in the concentration of neurotransmitters, especially of the GABA inhibitors, possible due to a neuronal fatigue provoked by the abnormal ring rate of the neurons during the seizure. 4.5 Application to alpha responses of visual event-related potentials 4.5.1 Introduction EEG alpha rhythms can be dened as oscillations between 8 and 13 Hz, with an amplitude usually below 50V and localized over posterior regions of the head. Alpha rhythms appear spontaneously during wakefulness, best seen with eyes closed, under relaxation and mental inactivity conditions (Niedermeyer, 1993a). Although alpha oscillations have been widely studied, their sources and functional correlates are still under discussion. Sources of alpha rhythms have been investigated leading to controversies whether they are thalamic, cortical or whether other structures are involved in their generation (Adrian, 1941 Andersen and Andersson, 1968 Lopes da 50
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Quantitative analysis of EEG signal
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1. Berichterstatter: Prof. Dr.-Ing.
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an okzipitalen Positionen und (c) d
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To my family: Mama, Consuelo, Hugui
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Preface In this work, I will descri
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I would certainly like to remember
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Contents Zusammenfassung Preface Ac
Page 16 and 17: 5.2.6 Calculating Lyapunov Exponent
Page 18 and 19: Summary Since the rsts recordings i
Page 20 and 21: 1 Outline of Neurophysiology: Brain
Page 22 and 23: Figure 2: Normal 20 channels (10-20
Page 24 and 25: 1.1.2 EEG in Epilepsy One important
Page 26 and 27: Figure 3: Scalp EEG of 18 channels
Page 28 and 29: Figure 4: Averaged responses upon N
Page 30 and 31: 2 Fourier Transform 2.1 Introductio
Page 32 and 33: I xx (k) =jX(k)j 2 = X(k) X (k) (
Page 34 and 35: 17 Figure 5: Topographical mapping
Page 36 and 37: 1987) is that coherence gives the c
Page 38 and 39: 3 Gabor Transform (Short Time Fouri
Page 40 and 41: where k g D k= R 1 ;1 jg D(t 0 )j 2
Page 42 and 43: and the band maximum peak frequency
Page 44 and 45: Figure 7: Intracraneal seizure reco
Page 46 and 47: Figure 10: Mean (soft line) and max
Page 48 and 49: EEG as the one with least amount of
Page 50 and 51: Figure 11: Scalp EEG of the right c
Page 52 and 53: 3.5 Conclusion In this chapter I de
Page 54 and 55: Original signal FOURIER TRANSFORM G
Page 56 and 57: 4.2.3 Multiresolution Analysis Cont
Page 58 and 59: Original signal -15 0 15 -1sec 0 1s
Page 60 and 61: 4.2.5 Wavelet Packets In the approa
Page 62 and 63: marked decrease in computational ti
Page 64 and 65: ain activity during an epileptic se
Page 68 and 69: Silva et al.,1973a,1973b Lopes da S
Page 70 and 71: sweep #1 sweep #2 sweep #3 sweep #4
Page 72 and 73: VEP non-target target F3 F4 F3 F4 F
Page 74 and 75: VEP non-target target F3 F4 F3 F4 F
Page 76 and 77: Electrode F3 F4 Cz P3 P4 O1 O2 Dela
Page 78 and 79: In conclusion, our results point to
Page 80 and 81: 63 Figure 22: Gamma responses for a
Page 82 and 83: Figure 24: T-test comparison of the
Page 84 and 85: wavelet coecients allowed an easy d
Page 86 and 87: the position vs. the linear momentu
Page 88 and 89: unknown topology it is necessary to
Page 90 and 91: the sum of the positive exponents (
Page 92 and 93: performed. On one hand, must be lar
Page 94 and 95: Duke (1992) and Elbert et al. (1994
Page 96 and 97: agation time. They applied this pro
Page 98 and 99: Figure 28: Histogram for the EEG da
Page 100 and 101: Figure 29: Attractors corresponding
Page 102 and 103: able for automatic detection proces
Page 104 and 105: ENTROPY Thermodynamics Signal analy
Page 106 and 107: 6.3 Application to visual event-rel
Page 108 and 109: VEP Non Target Target F3 -20 -10 0
Page 110 and 111: 1 VEP NON-TARGET TARGET 1 1 F3 F3 0
Page 112 and 113: 1 VEP NON-TARGET TARGET 1 1 F3 F3 0
Page 114 and 115: and the Lorenz equations (a model o
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P300 deection. Due to the relation
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7 General Discussion In this chapte
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Wavelet analysis was also applied t
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aect the whole spectrum and for thi
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peaks. 7.2.3 Wavelet Transform vs.
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the ones having wide peaks (being t
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A Time-frequency resolution and the
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Z 1 ;1 tx(t) d dt x(t) dt = 1 2 Z 1
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Figure 37: Time-frequency resolutio
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References Abarbanel HDI, Brown R,
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Berger, H. Uber das Elektrenkephalo
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Gastaut H and Broughton R. Epilepti
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Lopes da Silva FH, van Lierop THMT,
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Pradhan N, Sadasivan P, Chatterji S
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Serrano E, Ph.D. Thesis, Department
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Biographical sketch 21.03.1967 born
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