RESUMEN
Spreading depression (SD), a self-propagating wave of astroglial and neuronal depolarization, is an accompaniment of several neurological disorders including epilepsy. Its well-described features are initial depolarization, followed by EEG flattening. In this in vivo study in awake animals, the relationship of SDs to epileptiform activity was re-examined. We assessed SDs generated by mechanical stimulation and by metabolic inhibition with fluorocitrate. In addition to identifying prolonged EEG depression, we identified two periods, one prior to and another during depression, characterized by increases in power of specific frequencies that were sometimes associated with epileptiform discharges. The first period was characterized by ripple activity close to the induction site (88% of SDs with intracortical electrodes). The second period was characterized by localized low-frequency spikes (100% with dural screw electrodes, 65% with intracortical electrodes). By using fluorocitrate to induce SDs, the initial period was also characterized by runs of spikes (52%). Finally, with SDs induced by both methods, there was a period at the end of depression when additional, unprovoked SDs occurred (20%). Five stages of SD were defined by these phenomena, in the order: excitation, depression, excitation, depression, SD, with metabolic inhibition enhancing the expression of epileptiform spiking.
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Ondas Encefálicas/fisiología , Encéfalo/fisiología , Depresión de Propagación Cortical/fisiología , Sincronización de Fase en Electroencefalografía/fisiología , Animales , Electroencefalografía , Lateralidad Funcional , Miembro Posterior/inervación , Masculino , Espectrometría de Masas , Estimulación Física , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
OBJECTIVE: In publications on the electroencephalographic (EEG) features of psychoses and other disorders, various methods are utilized to diminish electromyogram (EMG) contamination. The extent of residual EMG contamination using these methods has not been recognized. Here, we seek to emphasize the extent of residual EMG contamination of EEG. METHODS: We compared scalp electrical recordings after applying different EMG-pruning methods with recordings of EMG-free data from 6 fully paralyzed healthy subjects. We calculated the ratio of the power of pruned, normal scalp electrical recordings in the six subjects, to the power of unpruned recordings in the same subjects when paralyzed. We produced "contamination graphs" for different pruning methods. RESULTS: EMG contamination exceeds EEG signals progressively more as frequencies exceed 25 Hz and with distance from the vertex. In contrast, Laplacian signals are spared in central scalp areas, even to 100 Hz. CONCLUSION: Given probable EMG contamination of EEG in psychiatric and other studies, few findings on beta- or gamma-frequency power can be relied upon. Based on the effectiveness of current methods of EEG de-contamination, investigators should be able to reanalyze recorded data, reevaluate conclusions from high-frequency EEG data, and be aware of limitations of the methods.
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Trastornos Psicóticos , Cuero Cabelludo , Electroencefalografía/métodos , Electromiografía/métodos , Humanos , Trastornos Psicóticos/diagnósticoRESUMEN
OBJECTIVE: To present a new, automated and fast artefact-removal approach which significantly reduces the effect of contamination in scalp electrical recordings. METHOD: We used spectral and temporal characteristics of different sources recorded during a typical scalp electrical recording in order to improve a fast and effective artefact removal approach. Our experiments show that correlation coefficient and spectral gradient of brain components differ from artefactual components. We trained two binary support vector machine classifiers such that one separates brain components from muscle components, and the other separates brain components from mains power and environmental components. We compared the performance of the proposed approach with seven currently used alternatives on three datasets, measuring mains power artefact reduction, muscle artefact reduction and retention of brain neurophysiological responses. RESULTS: The proposed approach significantly reduces the main power and muscle contamination from scalp electrical recording without affecting brain neurophysiological responses. None of the competitors outperformed the new approach. CONCLUSIONS: The proposed approach is the best choice for artefact reduction of scalp electrical recordings. Further improvements are possible with improved component analysis algorithms. SIGNIFICANCE: This paper provides a definitive answer to an important question: Which artefact removal algorithm should be used on scalp electrical recordings?
Asunto(s)
Algoritmos , Artefactos , Encéfalo/fisiología , Electroencefalografía/métodos , Músculos/fisiología , Cuero Cabelludo/fisiología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Niño , Femenino , Humanos , Masculino , Persona de Mediana Edad , Adulto JovenRESUMEN
We recorded scalp electrical activity before and after full neuro-muscular paralysis in 5 volunteers and determined differences due to elimination of muscular activity on several standard applications of EEG. Due to paralysis, there were reductions in 'noisiness' of the standard scalp recordings which were maximal over the peripheral scalp, not explained by abolition of movement artefact, and best accounted for by sustained EMG activity in resting individuals. There was a corresponding reduction in spectral power in the gamma range. In central leads, the extent of gamma frequency coherence during a non-time-locked mental task (1 s epochs) was reduced by paralysis, likely due to a reduction in gamma-frequency coherence in widely arising EMG signals. In a time-locked mental task (auditory oddball), evoked responses were qualitatively unaffected by paralysis but 3 of 4 induced gamma responses were obscured by EMG.
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Encéfalo/fisiología , Músculo Esquelético/fisiología , Artefactos , Electroencefalografía , Electromiografía , Mano , Humanos , Procesos Mentales/fisiología , Actividad Motora/fisiología , Pruebas Neuropsicológicas , Parálisis/fisiopatología , Descanso/fisiología , Cuero CabelludoRESUMEN
BACKGROUND: Pulsatile GH secretion from the anterior pituitary is a key mediator of human growth regulation and is affected by a number of genetic and environmental factors. Activation of neuronal nicotinic acetylcholine (nACh) receptors promotes GH release, but the role of these receptors in growth regulation is unknown. AIM: Our aim was to assess the effect of a mutation in the alpha4 subunit of the nACh receptor on cholinergic-mediated GH release. METHODS: Forty-one healthy volunteers (24 male, age 36.2 +/- 12.2 yr, mean +/- sd) and 13 subjects with the alpha4-Ser248Phe mutation (four male, age 43.2 +/- 16.8 yr) were studied. Serum levels of GH, LH, FSH, prolactin, TSH, free T(4), and cortisol were measured at baseline and at regular intervals after infusion of physostigmine. Height and weight were recorded in all participants as well as from additional family members with (n = 11, four male) and without (n = 16, seven male) the mutation. RESULTS: Subjects with the mutation were shorter (1.62 +/- 0.08 vs. 1.72 +/- 0.09 m, P < 0.05) and had a greater body mass index (31 +/- 6 vs. 24 +/- 3 kg/m(2), P < 0.05) than healthy volunteers and unaffected members of the pedigree. In controls, physostigmine markedly increased the serum levels of GH (mean increase, +732%). In contrast, the response to physostigmine was markedly blunted in subjects with the mutation (+104%, P > 0.2 vs. control). CONCLUSIONS: These findings suggest a role of the nACh receptor in human growth regulation.
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Estatura/genética , Trastornos del Crecimiento/genética , Hormona de Crecimiento Humana/fisiología , Receptores Nicotínicos/genética , Adolescente , Adulto , Anciano , Índice de Masa Corporal , Inhibidores de la Colinesterasa/farmacología , Femenino , Hormona Folículo Estimulante/sangre , Trastornos del Crecimiento/sangre , Hormona de Crecimiento Humana/sangre , Humanos , Hidrocortisona/sangre , Hormona Luteinizante/sangre , Masculino , Persona de Mediana Edad , Fisostigmina/farmacología , Mutación Puntual , Prolactina/sangre , Tirotropina/sangre , Tiroxina/sangreRESUMEN
OBJECTIVE: Fast electrical rhythms in the gamma range (30-100Hz) in scalp (but not intracranial) recordings are predominantly due to electromyographic (EMG) activity. We hypothesized that increased EMG activity would be augmented by mental tasks in proportion to task difficulty and the requirement of these tasks for motor or visuo-motor output. METHODS: EEG was recorded in 98 subjects whilst performing cognitive tasks and analysed to generate power spectra. In four other subjects, neuromuscular blockade was achieved pharmacologically providing EMG-free spectra of EEG at rest and during mental tasks. RESULTS: In comparison to the paralysed condition, power of scalp electrical recordings in the gamma range varied in distribution, being maximal adjacent to cranial or cervical musculature. There were non-significant changes in mean gamma range activity due to mental tasks in paralysed subjects. In normal subjects, increases in scalp electrical activity were observed during tasks, without relationship to task difficulty, but with tasks involving limb- or eye-movement having higher power. CONCLUSIONS: Electrical rhythms in the gamma frequency range recorded from the scalp are inducible by mental activity and are largely due to EMG un-related to cognitive effort. EMG varies with requirements for somatic or ocular movement more than task difficulty. SIGNIFICANCE: Severe restrictions exist on utilizing scalp recordings for high frequency EEG.
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Artefactos , Electroencefalografía , Electromiografía , Cuero Cabelludo/fisiología , Pensamiento/fisiología , Adulto , Anciano , Atracurio/análogos & derivados , Atracurio/farmacología , Encéfalo/fisiología , Electroencefalografía/efectos de los fármacos , Electromiografía/efectos de los fármacos , Humanos , Masculino , Persona de Mediana Edad , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/fisiología , Bloqueantes Neuromusculares/farmacología , Parálisis/inducido químicamente , Cuero Cabelludo/efectos de los fármacos , Cuero Cabelludo/inervación , Pensamiento/efectos de los fármacosRESUMEN
It is currently unknown what processes take place at the interface between non-ictal and ictal activity during seizure initiation. In this study, using paralysed awake rats, we focally inhibited astrocytic metabolism with fluorocitrate (FC), causing seizures. We measured changes in electroencephalogram (EEG) (0-300 Hz), and extracellular ion-concentrations during ictal onsets defining possible relationships with impedance-determined cell swelling. In animals showing ictal activity (69%) there were spike-wave discharges, spike-wave discharges followed by spreading depression and spreading depression without any discharges. In a high proportion of spike-wave discharges (>95%), just prior to the first spike-wave discharge, there was a decrease in the volume of the extracellular space. Following the initiation of cell swelling and prior to discharges, there were increases in high-frequency (150-300 Hz) EEG activity, increases in extracellular potassium- and decreases in extracellular calcium-concentrations. We suggest that EEG and ionic changes are not causative of cell swelling. Cell swelling due to metabolic failure in astrocytes at the injected site may release excitatory amino acids. At the same time, our results suggest ion homeostasis is not maintained and increased neuronal excitability and synchronisation occur. These could be the drivers changing normal brain activity into ictal activity.
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Edema Encefálico/etiología , Citratos , Depresión de Propagación Cortical/efectos de los fármacos , Líquido Extracelular/metabolismo , Convulsiones/inducido químicamente , Equilibrio Hidroelectrolítico/fisiología , Animales , Calcio/metabolismo , Depresión de Propagación Cortical/fisiología , Modelos Animales de Enfermedad , Impedancia Eléctrica , Electroencefalografía/efectos de los fármacos , Electroencefalografía/métodos , Masculino , Potasio/metabolismo , Ratas , Ratas Sprague-Dawley , Convulsiones/fisiopatología , Factores de TiempoRESUMEN
OBJECTIVE: To compare comprehensive measures of scalp-recorded muscle activity in migraineurs and controls. METHOD: We used whole-of-head high-density scalp electrical recordings, independent component analysis (ICA) and spectral slope of the derived components, to define muscle (electromyogram-containing) components. After projecting muscle components back to scalp, we quantified scalp spectral power in the frequency range, 52-98â¯Hz, reflecting muscle activation. We compared healthy subjects (nâ¯=â¯65) and migraineurs during a non-headache period (nâ¯=â¯26). We also examined effects due to migraine severity, gender, scalp-region and task (eyes-closed and eyes-open). We could not examine the effect of pre-ictal versus inter-ictal versus post-ictal as this information was not available in the pre-existing dataset. RESULTS: There was more power due to muscle activity (mean⯱â¯SEM) in migraineurs than controls (respectively, -13.61⯱â¯0.44â¯dB versus -14.73⯱â¯0.24â¯dB, pâ¯=â¯0.028). Linear regression showed no relationship between headache frequency and muscle activity in any combination of region and task. There was more power during eyes-open than eyes-closed (respectively, -13.42⯱â¯0.34â¯dB versus -14.92⯱â¯0.34â¯dB, pâ¯=â¯0.002). CONCLUSIONS: There is an increase in cranial and upper cervical muscle activity in non-ictal migraineurs versus controls. This raises questions of the role of muscle in migraine, and the possible differentiation of non-ictal phases. SIGNIFICANCE: This provides preliminary evidence to date of possible cranial muscle involvement in migraine.
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Trastornos Migrañosos/fisiopatología , Músculos del Cuello/fisiopatología , Adulto , Electroencefalografía , Electromiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Descanso/fisiología , Cuero Cabelludo/fisiopatologíaRESUMEN
BACKGROUND: Contamination of scalp measurement by tonic muscle artefacts, even in resting positions, is an unavoidable issue in EEG recording. These artefacts add significant energy to the recorded signals, particularly at high frequencies. To enable reliable interpretation of subcortical brain activity, it is necessary to detect and discard this contamination. NEW METHOD: We introduce a new automatic muscle-removal approach based on the traditional Blind Source Separation-Canonical Correlation Analysis (BSS-CCA) method and the spectral slope of its components. We show that CCA-based muscle-removal methods can discriminate between signals with high correlation coefficients (brain, mains artefact) and signals with low correlation coefficients (white noise, muscle). We also show that typical BSS-CCA components are not purely from one source, but are mixtures from multiple sources, limiting the performance of BSS-CCA in artefact removal. We demonstrate, using our paralysis dataset, improved performance using BSS-CCA followed by spectral-slope rejection. RESULT: This muscle removal approach can reduce high-frequency muscle contamination of EEG, especially at peripheral channels, while preserving steady-state brain responses in cognitive tasks. COMPARISON WITH EXISTING METHODS: This approach is automatic and can be applied on any sample of data easily. The results show its performance is comparable with the ICA method in removing muscle contamination and has significantly lower computational complexity. CONCLUSION: We identify limitations of the traditional BSS-CCA approach to artefact removal in EEG, propose and test an extension based on spectral slope that makes it automatic and improves its performance, and results in performance comparable to competitors such as ICA-based artefact removal.
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Artefactos , Electroencefalografía/métodos , Reconocimiento de Normas Patrones Automatizadas/métodos , Procesamiento de Señales Asistido por Computador , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Encéfalo/fisiología , Niño , Electromiografía , Movimientos Oculares/efectos de los fármacos , Movimientos Oculares/fisiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/fisiología , Bloqueo Neuromuscular , Percepción/fisiología , Mejoramiento de la Calidad , Cuero Cabelludo/efectos de los fármacos , Cuero Cabelludo/fisiología , Adulto JovenRESUMEN
OBJECTIVE: To identify the possible contribution of electromyogram (EMG) to scalp electroencephalogram (EEG) rhythms at rest and induced or evoked by cognitive tasks. METHODS: Scalp EEG recordings were made on two subjects in presence and absence of complete neuromuscular blockade, sparing the dominant arm. The subjects undertook cognitive tasks in both states to allow direct comparison of electrical recordings. RESULTS: EEG rhythms in the paralysed state differed significantly compared with the unparalysed state, with 10- to 200-fold differences in the power of frequencies above 20 Hz during paralysis. CONCLUSIONS: Most of the scalp EEG recording above 20 Hz is of EMG origin. Previous studies measuring gamma EEG need to be re-evaluated. SIGNIFICANCE: This has a significant impact on measurements of gamma rhythms from the scalp EEG in unparalysed humans. It is to be hoped that signal separation methods will be able to rectify this situation.
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Artefactos , Electroencefalografía , Electromiografía , Parálisis/fisiopatología , Cuero Cabelludo/fisiopatología , Estimulación Acústica/métodos , Humanos , Masculino , Procesos Mentales , Bloqueantes Neuromusculares , Parálisis/diagnóstico , Parálisis/psicología , Estimulación LuminosaRESUMEN
BACKGROUND: Cranial and cervical muscle activity (electromyogram, EMG) contaminates the surface electroencephalogram (EEG) from frequencies below 20 through to frequencies above 100Hz. It is not possible to have a reliable measure of cognitive tasks expressed in EEG at gamma-band frequencies until the muscle contamination is removed. NEW METHOD: In the present work, we introduce a new approach of using a minimum-norm based beamforming technique (sLORETA) to reduce tonic muscle contamination at sensor level. Using a generic volume conduction model of the head, which includes three layers (brain, skull, and scalp), and sLORETA, we estimated time-series of sources distributed within the brain and scalp. The sources within the scalp were considered to be muscle and discarded in forward modelling. RESULT: (1) The method reduced EMG contamination, more strongly at peripheral channels; (2) task-induced cortical activity was retained or revealed after removing putative muscle activity. COMPARISON WITH EXISTING METHODS: This approach can decrease tonic muscle contamination in scalp measurements without relying on time-consuming processing of expensive MRI data. In addition, it is competitive to ICA in muscle reduction and can be reliably applied on any length of recorded data that captures the dynamics of the signals of interest. CONCLUSION: This study suggests that sLORETA can be used as a method to quantitate cranial muscle activity and reduce its contamination at sensor level.
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Encéfalo/fisiología , Procesamiento Automatizado de Datos , Potenciales Evocados Motores/fisiología , Músculos/fisiología , Estimulación Acústica , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Mapeo Encefálico , Niño , Electroencefalografía , Electromiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estimulación Luminosa , Análisis Espectral , Adulto JovenRESUMEN
Independent Component Analysis (ICA) is a powerful statistical tool capable of separating multivariate scalp electrical signals into their additive independent or source components, specifically EEG or electroencephalogram and artifacts. Although ICA is a widely accepted EEG signal processing technique, classification of the recovered independent components (ICs) is still flawed, as current practice still requires subjective human decisions. Here we build on the results from Fitzgibbon et al. [1] to compare three measures and three ICA algorithms. Using EEG data acquired during neuromuscular paralysis, we tested the ability of the measures (spectral slope, peripherality and spatial smoothness) and algorithms (FastICA, Infomax and JADE) to identify components containing EMG. Spatial smoothness showed differentiation between paralysis and pre-paralysis ICs comparable to spectral slope, whereas peripherality showed less differentiation. A combination of the measures showed better differentiation than any measure alone. Furthermore, FastICA provided the best discrimination between muscle-free and muscle-contaminated recordings in the shortest time, suggesting it may be the most suited to EEG applications of the considered algorithms. Spatial smoothness results suggest that a significant number of ICs are mixed, i.e. contain signals from more than one biological source, and so the development of an ICA algorithm that is optimised to produce ICs that are easily classifiable is warranted.
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Algoritmos , Artefactos , Electroencefalografía , Procesamiento de Señales Asistido por Computador , Humanos , Cuero CabelludoRESUMEN
Meditative techniques aim for and meditators report states of mental alertness and focus, concurrent with physical and emotional calm. We aimed to determine the electroencephalographic (EEG) correlates of five states of Buddhist concentrative meditation, particularly addressing a correlation with meditative level. We studied 12 meditators and 12 pair-matched meditation-naïve participants using high-resolution scalp-recorded EEG. To maximise reduction of EMG, data were pre-processed using independent component analysis and surface Laplacian transformed data. Two non-meditative and five meditative states were used: resting baseline, mind-wandering, absorptions 1, 2, 3, 4 and 5 (corresponding to four levels of absorption and an absorption with a different object of focus, otherwise equivalent to level 4; these five meditative states produce repeatable, distinctly different experiences for experienced meditators). The experimental protocol required participants to experience the states in the order listed above, followed immediately by the reverse. We then calculated EEG power in standard frequency bands from 1 to 80Hz. We observed decreases of central scalp beta (13-25Hz), and central low gamma (25-48Hz) power in meditators during deeper absorptions. In contrast, we identified increases in frontal midline and temporo-parietal theta power in meditators, again, during deeper absorptions. Alpha activity was increased over all meditative states, not depth-related. This study demonstrates that the subjective experiences of deepening meditation partially correspond to measures of EEG. Our results are in accord with prior studies on non-graded meditative states. These results are also consistent with increased theta correlating with tightness of focus, and reduced beta/gamma with the desynchronization associated with enhanced alertness.
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Ritmo beta/fisiología , Corteza Cerebral/fisiología , Sincronización de Fase en Electroencefalografía/fisiología , Ritmo Gamma/fisiología , Meditación , Ritmo Teta/fisiología , Adulto , Budismo , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
OBJECTIVE: In a systematic study of gamma activity in neuro-psychiatric disease, we unexpectedly observed distinctive, apparently persistent, electroencephalogram (EEG) spectral peaks in the gamma range (25-100 Hz). Our objective, therefore, was to examine the incidence, distribution and some of the characteristics of these peaks. METHODS: High sample-rate, 128-channel, EEG was recorded in 603 volunteers (510 with neuropsychiatric disorders, 93 controls), whilst performing cognitive tasks, and converted to power spectra. Peaks of spectral power, including in the gamma range, were determined algorithmically for all electrodes. To determine if peaks were stable, 24-h ambulatory recordings were obtained from 16 subjects with peaks. In 10 subjects, steady-state responses to stimuli at peak frequency were compared with off-peak-frequency stimulation to determine if peaks were a feature of underlying network resonances and peaks were evaluated with easy and hard versions of oddball tasks to determine if peaks might be influenced by mental effort. RESULTS: 57% of 603 subjects exhibited peaks >2 dB above trough power at or above 25 Hz. Larger peaks (>5 dB) were present in 13% of subjects. Peaks were distributed widely over the scalp, more frequent centrally. Peaks were present through the day and were suppressed by slow-wave-sleep. Steady-state responses were the same with on- or off-peak sensory stimulation. In contrast, mental effort resulted in reductions in power and frequency of gamma peaks, although the suppression did not correlate with level of effort. CONCLUSIONS: Gamma EEG can be expressed constitutively as concentrations of power in narrow or wide frequency bands that play an, as yet, unknown role in cognitive activity. SIGNIFICANCE: These findings expand the described range of rhythmic EEG phenomena. In particular, in addition to evoked, induced and sustained gamma band activity, gamma activity can be present constitutively in spectral peaks.
RESUMEN
The objective of this paper was to investigate the effects of surface Laplacian processing on gross and persistent electromyographic (EMG) contamination of electroencephalographic (EEG) signals in electrical scalp recordings. We made scalp recordings during passive and active tasks, on awake subjects in the absence and in the presence of complete neuromuscular blockade. Three scalp surface Laplacian estimators were compared to left ear and common average reference (CAR). Contamination was quantified by comparing power after paralysis (brain signal, B) with power before paralysis (brain plus muscle signal, B+M). Brain:Muscle (B:M) ratios for the methods were calculated using B and differences in power after paralysis to represent muscle (M). There were very small power differences after paralysis up to 600 Hz using surface Laplacian transforms (B:M > 6 above 30 Hz in central scalp leads). Scalp surface Laplacian transforms reduce muscle power in central and pericentral leads to less than one sixth of the brain signal, two to three times better signal detection than CAR. Scalp surface Laplacian transformations provide robust estimates for detecting high-frequency (gamma) activity, for assessing electrophysiological correlates of disease, and also for providing a measure of brain electrical activity for use as a standard in the development of brain/muscle signal separation methods.
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Electroencefalografía/métodos , Músculo Esquelético/fisiología , Cuero Cabelludo/fisiología , Procesamiento de Señales Asistido por Computador , Adulto , Anciano , Electromiografía/métodos , Potenciales Evocados Visuales/fisiología , Femenino , Humanos , Masculino , Persona de Mediana Edad , Análisis y Desempeño de TareasRESUMEN
RATIONALE: Paralyzed human volunteers (n = 6) participated in several studies the primary one of which required full neuromuscular paralysis while awake. After the primary experiment, while still paralyzed and awake, subjects undertook studies of humor and of attempted eye-movement. The attempted eye-movements tested a central, intentional component to one's internal visual model and are the subject of this report. METHODS: Subjects reclined in a supportive chair and were ventilated after paralysis (cisatracurium, 20 mg intravenously). In illumination, subjects were requested to focus alternately on the faces of investigators standing on the left and the right within peripheral vision. In darkness, subjects were instructed to look away from a point source of light. Subjects were to report their experiences after reversal of paralysis. RESULTS: During attempted eye-movement in illumination, one subject had an illusion of environmental movement but four subjects perceived faces as clearly as if they were in central vision. In darkness, four subjects reported movement of the target light in the direction of attempted eye-movements and three could control the movement of the light at will. CONCLUSION: The hypothesis that internal visual models receive intended ocular-movement-information directly from oculomotor centers is strengthened by this evidence.
RESUMEN
Extracellular ion concentrations change during seizures in seizure models. [K(+)](o) increases and [Ca(2+)](o) decreases, resulting from population discharges, enhanced neuronal excitability, though not obviously before seizure onset. In acute pharmacological epilepsy models, there are striking increases in preictal high-frequency (gamma) electroencephalographic (EEG) activity. It is not known whether enhanced gamma EEG results in ionic changes, because gamma and ions have not been measured simultaneously. In this study, unanesthetized, paralyzed rats were given intravenous injections of kainic acid or picrotoxin to induce EEG discharges. Changes in EEG, [K(+)](o), and [Ca(2+)](o) in cortex and hippocampus were recorded. Kainic acid caused small [K(+)](o) fluctuations, without a temporal relationship of these with increased gamma EEG or with onset of discharges. Gamma EEG increases after picrotoxin also failed to affect [K(+)](o) and [Ca(2+)](o). Picrotoxin-induced electrical discharges led to [K(+)](o) rises of >9 mM and [Ca(2+)](o) falls of 0.1-0.2 mM. Kainic acid-induced discharges generated only moderate (2-3 mM) rises in [K(+)](o) and no changes in [Ca(2+)](o). In both models, there were large potassium rises (15-80 mM) and calcium falls (>0.5 mM), suggesting spreading depressions. Small [K(+)](o) fluctuations after kainic acid are consistent with disruption in potassium homeostasis, possibly because of depolarization of astrocytes. To reveal possible latent [K(+)](o) or [Ca(2+)](o) changes, we injected fluorocitrate intracortically to impair astrocytic function, before administering picrotoxin. Even fluorocitrate did not cause gamma-related ion changes but did cause low-magnitude, transient, potassium increases and slower potassium homeostasis during discharges, minor changes consistent with involvement of both astrocytes and neurons in [K(+)](o) regulation. (c) 2007 Wiley-Liss, Inc.
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Calcio/metabolismo , Electroencefalografía , Epilepsia/metabolismo , Líquido Extracelular/metabolismo , Potasio/metabolismo , Análisis de Varianza , Animales , Encéfalo/efectos de los fármacos , Encéfalo/fisiopatología , Relación Dosis-Respuesta a Droga , Electroencefalografía/efectos de los fármacos , Epilepsia/inducido químicamente , Epilepsia/fisiopatología , Líquido Extracelular/efectos de los fármacos , Ácido Kaínico/administración & dosificación , Masculino , Picrotoxina/administración & dosificación , Ratas , Ratas Sprague-Dawley , Análisis EspectralRESUMEN
PURPOSE: To test nicotine patch treatment for a patient with a defined mutation for autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) whose seizures were refractory to standard antiepileptic therapy. METHODS: Open and double-blind trials of nicotine patches in an "n-of-one" study. The double-blind trial comprised periods during which either placebo or nicotine patches were each used for three periods of 2 weeks, randomized in a double-blind manner. RESULTS: In an open study, nicotine patches reduced seizures from 1.65 +/- 2.36 to 0.01 +/- 0.0 seizures per day (p < 0.0001). In a double-blinded placebo-controlled phase, the average frequency of seizures on nicotine versus placebo was 0 +/- 0 versus 0.56 +/- 1.14 seizures per day (p < 0.0001). CONCLUSIONS: Nicotine patches may be of benefit to some individuals with ADNFLE.