ABSTRACT
Rasmussen syndrome is characterized by continuous partial seizures with progressive neurological/cognitive impairment. Currently the only effective treatment is surgery (hemispherectomy). The objective of our study is to detect the exact epileptogenic focus through the analysis of multimodal noninvasive and innocuous functional neuroimaging. The subject is a 5-year-old female patient with Rasmussen encephalopathy. Continuous and simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) was recorded. The sources of background and paroxysmal activity of EEG were computed by low resolution electromagnetic tomography (LORETA). Image analysis (SPM: statistic parametric mapping) was obtained for the areas where statistically significant differences in the fMRI BOLD response were computed, and the results from both techniques were compared. The main source of paroxysmal activity by EEG analysis was found in the anterolateral left hemisphere, with a significant increase in absolute and relative energies of slow frequency bands (theta-delta): Z > or = 3. The fMRI BOLD signal (basal vs. paroxysmal activity) was significantly different in the same region (t-test > or = 2.39). The generators of propagated paroxysmal activity were found in similar areas for both techniques. In conclusion, simultaneous EEG-fMRI recording allows the analysis of two harmless functional neuroimaging techniques separately and together in the same time period. In our case, it allowed the accurate delineation of epileptogenic foci and areas of spread with high spatiotemporal resolution, which is crucial for epilepsy surgery.
Subject(s)
Electroencephalography , Encephalitis/physiopathology , Encephalitis/surgery , Magnetic Resonance Imaging , Brain Mapping/methods , Child, Preschool , Female , Humans , Image Processing, Computer-Assisted , Neuropsychological TestsABSTRACT
Conventional EEG and quantitative EEG visual stimuli (close-open eyes) reactivity analysis have shown their usefulness in clinical practice; however studies at the level of EEG generators are limited. The focus of the study was visual reactivity of cortical resources in healthy subjects and in a stroke patient. The 64 channel EEG and T1 magnetic resonance imaging (MRI) studies were obtained from 32 healthy subjects and a middle cerebral artery stroke patient. Low Resolution Electromagnetic Tomography (LORETA) was used to estimate EEG sources for both close eyes (CE) vs. open eyes (OE) conditions using individual MRI. The t-test was performed between source spectra of the two conditions. Thresholds for statistically significant t values were estimated by the local false discovery rate (lfdr) method. The Z transform was used to quantify the differences in cortical reactivity between the patient and healthy subjects. Closed-open eyes alpha reactivity sources were found mainly in posterior regions (occipito-parietal zones), extended in some cases to anterior and thalamic regions. Significant cortical reactivity sources were found in frequencies different from alpha (lower t-values). Significant changes at EEG reactivity sources were evident in the damaged brain hemisphere. Reactivity changes were also found in the "healthy" hemisphere when compared with the normal population. In conclusion, our study of brain sources of EEG alpha reactivity provides information that is not evident in the usual topographic analysis.
Subject(s)
Alpha Rhythm/methods , Brain Ischemia/diagnosis , Brain Ischemia/physiopathology , Brain Mapping/methods , Brain/physiopathology , Evoked Potentials, Visual , Magnetic Resonance Imaging/methods , Adult , Female , Humans , Male , Middle AgedABSTRACT
Spectral features of EEG background activity were studied in patients with localized symptomatic epilepsy (LSE), with origin in the frontal or temporal lobes. Z-values of high resolution spectra and measures of the parametric (xi alpha) model of the EEG were obtained for all 10/20 System leads and were compared with those obtained in a control group. Comparisons were performed between syndromic variants of LSE and between subgroups of patients with or without paroxysmal activity in their digital EEGs (dEEG). Marked reduction of the energy in the alpha range and a mild increase in the theta range were found in the patients, unrelated to the syndromic variant of the epilepsy. These deviations from normality were widespread on the scalp and were not related to antiepileptic medication. Non-parametric testing showed a positive correlation between the magnitude of the quantitative EEG abnormalities and the amount of paroxysmal activity in the dEEG. Slowing of the mean frequency of alpha components of the spectra, an actual decrease of power in the alpha range and an increase in the theta range explained the results. The most striking finding of this paper is that focal epileptogenesis may have a generalized impact in the frequency composition of EEG.
Subject(s)
Electroencephalography , Epilepsy/physiopathology , Adolescent , Adult , Algorithms , Brain Mapping , Child , Humans , Middle Aged , Models, NeurologicalABSTRACT
Wavelet representation is a recent development in the analysis of non-stationary signals. Its possibilities for use in the description of time-frequency characteristics of both transients in spontaneous EEG and time-varying rhythms in event related brain activity are explored here. By way of illustration, multiresolution decompositions of a wide variety of EEG transients are carried out in this work, including spike-and-waves, single spikes, sharp waves, blink artifacts, frontal intermittent rhythmic delta activity (FIRDA) and paroxysmal delta activity. Also, the application of the wavelet representation to study related spectra perturbations is illustrated with data from psychophysical experiments on the perception of image motion. The results demonstrate the capabilities of the wavelet transform, as an alternative to the Fourier transform, for the representation and analysis of non-stationary EEG signals.
Subject(s)
Electroencephalography , Signal Processing, Computer-Assisted , Artifacts , Evoked Potentials , Fourier Analysis , Humans , Psychophysics , Reproducibility of Results , Time FactorsABSTRACT
In this paper statistical resampling techniques are used to support the presence of an equiangular first principal component in EEG log spectra and therefore the existence of a global scale factor in EEG recordings. the Log transformed spectra from a normal sample (n = 211, age 5-97) were analyzed. To reach this conclusion a method for estimating the scale factor is introduced. It is also shown that this factor remains constant in each individual for all derivations and frequencies and across functional states. The contribution of this scale factor to the overall variance of the normal EEG reaches 42% of the total variance of age corrected data. Part of the variance of the scale factor exhibits age dependency. Scale factor correction of EEG spectra data improves the diagnostic accuracy for detecting pathological EEG spectra from an almost random level (Area under the ROC curve = .6) to .84.
Subject(s)
Brain/physiology , Electroencephalography/statistics & numerical data , Adolescent , Adult , Age Factors , Aged , Analysis of Variance , Child , Child, Preschool , Female , Humans , Male , Mathematics , Middle Aged , Models, Statistical , Sensitivity and SpecificityABSTRACT
Brain Electromagnetic Topography (BET) has attained widespread use. The representation of EEG or MEG parameters as scalp maps (BETm) aids its clinical interpretation. However, some critical issues limit the usefulness of BETm. In particular, the conventional statistical assessment of BETm with respect to normative data is based upon marginal significance probability scales which involve multiple univariate comparisons (one at each recording site). As a consequence, the probability of false positive findings (type I error) is increased above its nominal level. The use of conservative levels avoids this phenomenon but results in a considerable increase of the probability of not detecting real abnormality (type II error). Furthermore, BETm are constructed without taking into consideration the patterns of correlations characteristic of electromagnetic data under normal states of brain functioning. This limits the capability of BETm of representing multivariate aspects of abnormality. This paper introduces some techniques to approach these difficulties. Multivariate Brain Electromagnetic Topographic maps (MBETm) are defined, which retain the attractive features of mapping but also take advantage of multivariate characteristics (in the spatial and frequency domains) to highlight aspects of neuropathology. Moreover, simultaneous significance probability (SSP) scales, valid for both BETm and MBETm, are introduced for the global control of the probability of a type I error. The use of these techniques is illustrated with data from patients with cortical tumours and with epilepsy. ROC analysis shows that in some cases there is a significant improvement in both detection and localization accuracy.
Subject(s)
Brain Mapping/methods , Brain/physiology , Magnetoencephalography , Electroencephalography , Humans , Multivariate Analysis , ProbabilityABSTRACT
For the past decade the Cuban Neuroscience Center has organized on behalf of the Ministry of Public Health of the Republic, a nationwide Program for the introduction of quantitative EEG (qEEG). This Program has involved a) development of standardized equipment for "paperless" EEG, qEEG and brain topography; b) establishment of a network of 21 laboratories of clinical neurophysiology; c) creation of the specialty of clinical neurophysiology which trains physicians from all provinces in both traditional and quantitative electrophysiological methods; d) introduction of standardized protocols for the collection of clinical and electrophysiological information; e) organization of a national normative and neuropsychiatric database; f) establishment of normative regression equations. Among the special issues discussed are: 1) relationship between traditional and quantitative methods; 2) evaluation of the effectiveness of the technology introduced; 3) use of qEEG in the early detection of brain dysfunction.
Subject(s)
Brain Diseases/diagnosis , Electroencephalography , Adolescent , Adult , Brain/physiopathology , Brain Diseases/classification , Brain Diseases/physiopathology , Brain Mapping , Child , Cuba , Health Services Administration , Humans , Learning Disabilities/diagnosis , Learning Disabilities/physiopathology , Longitudinal StudiesABSTRACT
BAEP records were obtained from 30 brain-dead patients. Three BAEP patterns were observed: (1) no identifiable waves (73.34%), (2) an isolated bilateral wave I (16.66%), and (3) an isolated unilateral wave I (10%). When wave I was present, it was always significantly delayed. Significant augmentation of wave I amplitude was present bilaterally in one case and unilaterally in another. On the other hand, in serial records from 3 cases wave I latency tended to increase progressively until this component disappeared. During the same period, wave I amplitude fluctuations were observed. A significant negative correlation was found for wave I latency with heart rate and body temperature in 1 case. Two facts might explain the progressive delay and disappearance of wave I in brain-dead patients: a progressive hypoxic-ischaemic dysfunction of the cochlea and the eighth nerve plus hypothermia, often present in brain-dead patients. Then the incidence of wave I preservation reported by different authors in single BAEP records from brain-dead patients might depend on the moment at which the evoked potential study was done in relation to the onset of the clinical state. It is suggested that, although BAEPs provide an objective electrophysiological assessment of brain-stem function, essential for BD diagnosis, this technique could be of no value for this purpose when used in isolation.
Subject(s)
Brain Death/physiopathology , Brain/physiopathology , Electroencephalography , Evoked Potentials, Auditory, Brain Stem , Adolescent , Adult , Aged , Aged, 80 and over , Child , Female , Humans , Male , Middle AgedABSTRACT
Se analiza el efecto producido por diferentes dosis de diazepam sobre el EEG de ratas utilizando las Medidas Espectrales de Banda Ancha y el Espectro de Potencia. De estas medidas las que presentan diferencias significativas son: Poder Relativo, Frecuencia Dominante y la Coherencia sólo para la dosis más alta: observándose mayor energia en las frecuencias más rápidas alfa y beta y menor energía para las frecuencias más lentas delta y theta. Estos resultados brindan la posibilidad de utilizar este método en la caracterización electroencefalográfia de drogas psicotrópicas relacionadas con los ansiolíticos (AU)
Subject(s)
Rats , Animals , Spectrum Analysis/methods , Diazepam/metabolism , ElectroencephalographyABSTRACT
La maniobra de apertura y cierre de los ojos es una de la más frecuentes en electroencefalografía para identificar el ritmo alfa por inspección visual. El objetivo principal de este trabajo es comprobar si mediante el análisis cuantitativo del EEG pueden detectarse los cambios que se observan, por inspección visual, entre segmentos de registro con los ojos abiertos y con los ojos cerrados. Para ello se recogió el EEG de 10 sujetos normales (25 a 35 años de edad) en las condiciones "ojos abiertos" y "ojoss cerrados" mediante un sistema computarizado de registro y análisis de EEG. A partir de los registros fueron obtenidos las medidas espectrales de banda ancha (MEBAS) y los parámetros del Modelo Xi-ALFA. Se encontró que los poderes absolutos, así como la frecuencia dominante son los que reflejan con mayor claridad un incremento de actividad en la banda alfa (regiones posteriores principalmente) en la condición "ojoss cerrados". Los parámetros del Modelo Xi-ALFA mostraron gran congruencia con las MEBAS. Se concluye que por medio del análisis cuantitativo del EEG se pueden detectar cambios en el EEG al comparar segmentos de registros con ojos abiertos, de segmentos con ojos cerrados (AU)
Subject(s)
Adult , Humans , Male , Female , Spectrum Analysis/methods , Electroencephalography , Computer SystemsABSTRACT
La maniobra de apertura y cierre de los ojos es una de la más frecuentes en electroencefalografía para identificar el ritmo alfa por inspección visual. El objetivo principal de este trabajo es comprobar si mediante el análisis cuantitativo del EEG pueden detectarse los cambios que se observan, por inspección visual, entre segmentos de registro con los ojos abiertos y con los ojos cerrados. Para ello se recogió el EEG de 10 sujetos normales (25 a 35 años de edad) en las condiciones "ojos abiertos" y "ojoss cerrados" mediante un sistema computarizado de registro y análisis de EEG. A partir de los registros fueron obtenidos las medidas espectrales de banda ancha (MEBAS) y los parámetros del Modelo Xi-ALFA. Se encontró que los poderes absolutos, así como la frecuencia dominante son los que reflejan con mayor claridad un incremento de actividad en la banda alfa (regiones posteriores principalmente) en la condición "ojoss cerrados". Los parámetros del Modelo Xi-ALFA mostraron gran congruencia con las MEBAS. Se concluye que por medio del análisis cuantitativo del EEG se pueden detectar cambios en el EEG al comparar segmentos de registros con ojos abiertos, de segmentos con ojos cerrados
Subject(s)
Humans , Male , Female , Adult , Electroencephalography , Spectrum Analysis/methods , Computer SystemsABSTRACT
Se analiza el efecto producido por diferentes dosis de diazepam sobre el EEG de ratas utilizando las Medidas Espectrales de Banda Ancha y el Espectro de Potencia. De estas medidas las que presentan diferencias significativas son: Poder Relativo, Frecuencia Dominante y la Coherencia sólo para la dosis más alta: observándose mayor energia en las frecuencias más rápidas alfa y beta y menor energía para las frecuencias más lentas delta y theta. Estos resultados brindan la posibilidad de utilizar este método en la caracterización electroencefalográfia de drogas psicotrópicas relacionadas con los ansiolíticos
