Uniform decrease of alpha-global field power induced by intermittent photic stimulation of healthy subjects

Rau, R.; Raschka, Christoph; Koch, Horst J.

doi:10.1590/s0100-879x2002000500014

Cited by 9 publications

(5 citation statements)

References 17 publications

(26 reference statements)

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“…Since each sensor was positioned in a distinct location around the head, the global spectrogram can be considered to be a "spatial summation" for each epoch of data. The underlying mathematical principles have been described in previous reports (Rau et al 2002). The neuromagnetic activity at each sensor was visualized with contour maps, which showed small spectrograms at the position of each MEG sensor.…”

Section: Discussionmentioning

confidence: 99%

Frequency and spatial characteristics of high‐frequency neuromagnetic signals in childhood epilepsy

Xiang

Liu

Wang

et al. 2009

Epileptic Disorders

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Purpose. Invasive intracranial recordings have suggested that high-frequency oscillation is involved in epileptogenesis and is highly localized to epileptogenic zones. The aim of the present study is to characterize the frequency and spatial patterns of high-frequency brain signals in childhood epilepsy using a non-invasive technology. Methods. Thirty children with clinically diagnosed epilepsy were studied using a whole head magnetoencephalography (MEG) system. MEG data were digitized at 4 000 Hz. The frequency and spatial characteristics of high-frequency neuromagnetic signals were analyzed using continuous wavelet transform and beamformer. Threedimensional magnetic resonance imaging (MRI) was obtained for each patient to localize magnetic sources. Results. Twenty-six patients showed highfrequency (100-1 000 Hz) components (26/30, 86%). Nineteen patients showed more than one high-frequency component (19/30, 63%). The frequency range of high-frequency components varied across patients. The highest frequency band was identified around 910 Hz. The loci of high-frequency epileptic activities were concordant with the lesions identified by magnetic resonance imaging for 21 patients (21/30, 70%). The MEG source localizations of high-frequency components were found to be concordant with intracranial recordings for nine of the eleven patients who underwent epilepsy surgery (9/11, 82%).Conclusion. The results have demonstrated that childhood epilepsy was associated with high-frequency epileptic activity in a wide frequency range. The concordance of MEG source localization, MRI and intracranial recordings suggests that measurement of high-frequency neuromagnetic signals might provide a novel approach for clinical management of childhood epilepsy.

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Section: Discussionmentioning

confidence: 99%

Frequency and spatial characteristics of high‐frequency neuromagnetic signals in childhood epilepsy

Xiang

Liu

Wang

et al. 2009

Epileptic Disorders

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“…Since each sensor was positioned in a distinct location around the brain if there was a subject, an accumulated global spectrogram should represent the magnetic field of the entire brain. The mathematical principles have been described in previous reports (Rau et al, 2002). The neuromagnetic activity at each sensor was visualized with contour maps, which showed small spectrograms at the position of each MEG sensor.…”

Section: Methodsmentioning

confidence: 99%

Accumulated source imaging of brain activity with both low and high-frequency neuromagnetic signals

Xiang

Luo

Kotecha

et al. 2014

Front. Neuroinform.

129

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Recent studies have revealed the importance of high-frequency brain signals (>70 Hz). One challenge of high-frequency signal analysis is that the size of time-frequency representation of high-frequency brain signals could be larger than 1 terabytes (TB), which is beyond the upper limits of a typical computer workstation's memory (<196 GB). The aim of the present study is to develop a new method to provide greater sensitivity in detecting high-frequency magnetoencephalography (MEG) signals in a single automated and versatile interface, rather than the more traditional, time-intensive visual inspection methods, which may take up to several days. To address the aim, we developed a new method, accumulated source imaging, defined as the volumetric summation of source activity over a period of time. This method analyzes signals in both low- (1~70 Hz) and high-frequency (70~200 Hz) ranges at source levels. To extract meaningful information from MEG signals at sensor space, the signals were decomposed to channel-cross-channel matrix (CxC) representing the spatiotemporal patterns of every possible sensor-pair. A new algorithm was developed and tested by calculating the optimal CxC and source location-orientation weights for volumetric source imaging, thereby minimizing multi-source interference and reducing computational cost. The new method was implemented in C/C++ and tested with MEG data recorded from clinical epilepsy patients. The results of experimental data demonstrated that accumulated source imaging could effectively summarize and visualize MEG recordings within 12.7 h by using approximately 10 GB of computer memory. In contrast to the conventional method of visually identifying multi-frequency epileptic activities that traditionally took 2–3 days and used 1–2 TB storage, the new approach can quantify epileptic abnormalities in both low- and high-frequency ranges at source levels, using much less time and computer memory.

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“…Some approaches to quantitative EEG topographic mapping may be used in the study of the complex spatial patterns of this phenomenon (25). However, all the aforementioned data concern adult subjects.…”

Section: Introductionmentioning

confidence: 99%

Topographic aspects of photic driving in the electroencephalogram of children and adolescents

Лазарев

Infantosi

Valencio-de-Campos

et al. 2004

Braz J Med Biol Res

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The electroencephalogram amplitude spectra at 11 fixed frequencies of intermittent photic stimulation of 3 to 24 Hz were combined into driving "profiles" for 14 scalp points in 8 male and 7 female normal subjects aged 9 to 17 years. The driving response varied over frequency and was detected in 70 to 100% of cases in the occipital areas (maximum) and in 27 to 77% of cases in the frontal areas (minimum) using as a criterion peak amplitude 20% higher than those of the neighbors. Each subject responded, on average, to 9.7 ± 1.15 intermittent photic stimulation frequencies in the right occipital area and to 6.8 ± 1.97 frequencies in the right frontal area. Most of the driving responses (in relation to the previous background) were significant according to the spectral F-test (α = 0.05), which also detected changes in some cases of low amplitude responses not revealed by the peak criterion. The profiles had two maxima in the alpha and theta bands in all leads. The latter was not present in the background spectra in the posterior areas and was less pronounced in the anterior ones. The weight of the profile theta maximum increased towards the frontal areas where the two maxima were similar, while the profile amplitudes decreased. The profiles repeated the shape of the background spectra, except for the theta band. The interhemispheric correlation between profiles was high. The theta driving detected in all areas recorded suggests a generalized influence of the theta generators in prepubertal and pubertal subjects.

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Uniform decrease of alpha-global field power induced by intermittent photic stimulation of healthy subjects

Cited by 9 publications

References 17 publications

Frequency and spatial characteristics of high‐frequency neuromagnetic signals in childhood epilepsy

Frequency and spatial characteristics of high‐frequency neuromagnetic signals in childhood epilepsy

Accumulated source imaging of brain activity with both low and high-frequency neuromagnetic signals

Topographic aspects of photic driving in the electroencephalogram of children and adolescents

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