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Chirp lattices in EEG waveforms
$230 resulting coefficients by a gain function. Filtered trials are reconstructed by applying a two-dimensional inverse Fourier transform to the filtered coefficients. The filter produces an improvement to the signal-to-noise ratio of 8 to 15 fold over the raw data. We have implemented two-dimensional real-time evoked potential reconstruction on a portable microcomputer system for use in the operating room. This system provides updated responses as often as every 5 seconds. Simultaneous display of middle and long-latency evoked potentials with associated EEG power spectra permits correlation of the evoked potential with changes in state.
several designated frequency bands (e.g., delta, theta, alpha and beta) is assigned colour values resulting in a schematic view of the distribution of electrical activity over the surface of the scalp. With this technique, regional drug effects can be readily visualized and displayed in compact form. We demonstrate the efficacy of this technique by plotting EEG maps pre- and postbarbiturate and pre- and post- benzodiazepine treatment. Drug-induced pre-central beta activity is readily visualized and quantified. The regional distribution of enhanced beta activity caused by an experimental anticonvulsant, zonisamide, is also demonstrated. Topographic maps are compared with simultaneously recorded 16 channel EEG and 16 channel CSA histograms.
DPW2.06 C H I R P L A T r I C E S IN EEG W A V E F O R M S . D.E. Maynard
DPW2.08 REAL T I M E EEG E N V E L O P E ANALYSIS BY M E A N S OF H O M O M O R P H I C FILTERING.
(London. UK)
V. Gimeno, T. Sagales and M.D. Calzada
EEG waveforms can be analysed in terms of the summation of a few amplitude and frequency-modulated sinusoids. These can be traced by inspection of sequential wideband phase spectra (Maynard, Nature, Lond. 1972, 236: 228). When relatively long filters are used (200 msec) to generate the spectra, discontinuous sinusoids varying slowly in frequency are detected. With short filters (80 msec) a latticework of sinusoids either rising or falling rapidly in frequency (chirps) (Maynard, Electroenceph. clin. Neurophysiol, 1981, 52: 26p) at rates of the order of 400Hz/sec, are found. The long and short filter analyses can be shown to have some equivalence. However, the chirp analysis is of particular interest. Firstly, because each chirp can be assigned a polarity according to its phase at closest approach to 0Hz. Secondly, because, with the probable exception of some delta band activity, this analysis enables the EEG to be described in terms of a summation of just two types of components: rising and falling frequency chirps. Thirdly, if each chirp should be found to represent a population of sequentially interacting groups of neurones, then the lattice could represent a process which synchronises such populations.
(Barcelona, Spain) For most EEG activity, the signal can be considered to be the product of two signals: the slowly varying envelope, always positive, and the much faster bipolar signal modulation. Thus, the methodology of homomorphic signal processing can be used to separate these two components. In this presentation we are only concerned with the elicitation of the envelope, and the study of its statistical features. A method is described, based on a small size, general-purpose computer with programmes designed to perform the full sequence of operations in real time. Therefore, this is a technique of EEG data processing that can be oriented towards the general problem of on-line EEG monitoring. This method has been tested in the evaluation of full night sleep recordings and a very good correlation with visual analysis of the data has been consistently obtained.
DPW2.09 E X T R A C T I O N O F O S C I L L A T O R Y P O T E N T I A L S IN H U M A N ERG BY DIGITAL FILTERING. A. P~;~kkOnen and V.J. Partanen
DPW2.07 C O L O U R T O P O G R A P H I C EEG M A P P I N G IN D R U G RESEARCH. E.J. Hammond, S.A. M o h a m m e d and B.J. Wilder
(Gainesville, FL, USA) Compressed spectral array (CSA) analysis is an efficient method to display a frequency analysis of E E G data. This method becomes cumbersome when a large number of channels are displayed. Colour topographic CSA mapping involves the transformation of electrical activity at each of m a n y recording sites on the head into an organized colour scheme shown as a picture of the head. The amplitude associated with each of
(Kuopio, Finland) The term oscillatory potentials (OPs) describes the wavelets superimposed on the ascending slope of the h u m a n electroretinogram. In diabetic retinopathy, for example, these potentials may be reduced while the amplitude of the primary components of the E R G is normal. Most commonly OPs have been recorded by using special stimulation conditions and electronic filtering. Our purpose was to extract OPs from standard recordings of the E R G in order to simplify our E R G practice and to avoid phase distortions introduced by electronic filtering. The recording protocol was based on the AEEGS Guidelines for Clinical
several designated frequency bands (e.g., delta, theta, alpha and beta) is assigned colour values resulting in a schematic view of the distribution of electrical activity over the surface of the scalp. With this technique, regional drug effects can be readily visualized and displayed in compact form. We demonstrate the efficacy of this technique by plotting EEG maps pre- and postbarbiturate and pre- and post- benzodiazepine treatment. Drug-induced pre-central beta activity is readily visualized and quantified. The regional distribution of enhanced beta activity caused by an experimental anticonvulsant, zonisamide, is also demonstrated. Topographic maps are compared with simultaneously recorded 16 channel EEG and 16 channel CSA histograms.
DPW2.06 C H I R P L A T r I C E S IN EEG W A V E F O R M S . D.E. Maynard
DPW2.08 REAL T I M E EEG E N V E L O P E ANALYSIS BY M E A N S OF H O M O M O R P H I C FILTERING.
(London. UK)
V. Gimeno, T. Sagales and M.D. Calzada
EEG waveforms can be analysed in terms of the summation of a few amplitude and frequency-modulated sinusoids. These can be traced by inspection of sequential wideband phase spectra (Maynard, Nature, Lond. 1972, 236: 228). When relatively long filters are used (200 msec) to generate the spectra, discontinuous sinusoids varying slowly in frequency are detected. With short filters (80 msec) a latticework of sinusoids either rising or falling rapidly in frequency (chirps) (Maynard, Electroenceph. clin. Neurophysiol, 1981, 52: 26p) at rates of the order of 400Hz/sec, are found. The long and short filter analyses can be shown to have some equivalence. However, the chirp analysis is of particular interest. Firstly, because each chirp can be assigned a polarity according to its phase at closest approach to 0Hz. Secondly, because, with the probable exception of some delta band activity, this analysis enables the EEG to be described in terms of a summation of just two types of components: rising and falling frequency chirps. Thirdly, if each chirp should be found to represent a population of sequentially interacting groups of neurones, then the lattice could represent a process which synchronises such populations.
(Barcelona, Spain) For most EEG activity, the signal can be considered to be the product of two signals: the slowly varying envelope, always positive, and the much faster bipolar signal modulation. Thus, the methodology of homomorphic signal processing can be used to separate these two components. In this presentation we are only concerned with the elicitation of the envelope, and the study of its statistical features. A method is described, based on a small size, general-purpose computer with programmes designed to perform the full sequence of operations in real time. Therefore, this is a technique of EEG data processing that can be oriented towards the general problem of on-line EEG monitoring. This method has been tested in the evaluation of full night sleep recordings and a very good correlation with visual analysis of the data has been consistently obtained.
DPW2.09 E X T R A C T I O N O F O S C I L L A T O R Y P O T E N T I A L S IN H U M A N ERG BY DIGITAL FILTERING. A. P~;~kkOnen and V.J. Partanen
DPW2.07 C O L O U R T O P O G R A P H I C EEG M A P P I N G IN D R U G RESEARCH. E.J. Hammond, S.A. M o h a m m e d and B.J. Wilder
(Gainesville, FL, USA) Compressed spectral array (CSA) analysis is an efficient method to display a frequency analysis of E E G data. This method becomes cumbersome when a large number of channels are displayed. Colour topographic CSA mapping involves the transformation of electrical activity at each of m a n y recording sites on the head into an organized colour scheme shown as a picture of the head. The amplitude associated with each of
(Kuopio, Finland) The term oscillatory potentials (OPs) describes the wavelets superimposed on the ascending slope of the h u m a n electroretinogram. In diabetic retinopathy, for example, these potentials may be reduced while the amplitude of the primary components of the E R G is normal. Most commonly OPs have been recorded by using special stimulation conditions and electronic filtering. Our purpose was to extract OPs from standard recordings of the E R G in order to simplify our E R G practice and to avoid phase distortions introduced by electronic filtering. The recording protocol was based on the AEEGS Guidelines for Clinical