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PubMed1995

A spatial oculomotor memory-task performance produces a task-related slow shift in human electroencephalography.

Electroencephalographic (EEG) deflections in humans related to the performance of memory-guided saccades were studied in this work. The EEG deflections were recorded during 2 spatial oculomotor delayed response tasks in which the subject was instructed to make a saccade either to the right or to the left depending on the spatial location of the cue which had been shown in the beginning of the delay period. The EEG deflections were compared to those recorded during a control task in which the subject also made a saccade to the right or to the left after a delay but the requirement to keep spatial information actively in mind was minimized. A slow delay-related shift was recorded during all task conditions. The slow shift was positive in the most frontal and negative in the more posterior recording sites. The negative slow shift in the more posterior recording sites was larger in the memory tasks than in the control task. Since the memory and the control tasks differed mainly in their requirement to hold spatial information in mind it is suggested that the difference in the magnitude of slow shifts between the memory and the control tasks reflects neural activity related to spatial working memory. But although the oculomotor responses in all tasks were similar, the preparatory activities for the impending eye movements may not have been similar and in addition to working memory may have contributed to the observed differences in the slow shifts.

Adult↗
PubMed1994

A simultaneous electrocardiogram is important when electroencephalography is used in the evaluation of loss of consciousness.

This study examined the use of electroencephalograms (EEGs) in 2 groups of patients with loss of consciousness (LOC), and the importance of a simultaneous electrocardiogram (ECG). Each group consisted of 75 patients referred for EEG. Group 1 patients (LOC without an established cause) had no clear history of convulsive disorder, while group 2 patients (LOC secondary to epilepsy) did. In all patients, it was ascertained if any previous cardiac investigations had been performed. All patients had an EEG performed with a simultaneous ECG. In addition to reporting the EEG, the neurologist reviewed the ECG rhythm and QRS morphology from the strip recording in an attempt to use this as a cardiac screening test. A cardiologist with the availability of all strip recordings and a subsequent 12 lead ECG reviewed his findings. The ECG was classified as significantly abnormal (potentially capable of causing syncope) in 17% of group 1 patients and 5% of group 2. The neurologist, using the simultaneous ECG strip recording only, correctly identified 14 of the 17 significantly abnormal ECGs (84%) and 127 of the 133 normal cases. In most cases, this was the only ECG evaluation as the EEG was performed without any prior cardiac investigation in 53% of group 1 patients and 92% of group 2. In conclusion, the EEG was often used as an initial investigation in these patients with LOC. A simultaneous ECG strip enabled the neurologist to detect most patients with significantly abnormal ECGs or rhythm. This will allow appropriate early cardiac review of these patients.

Adolescent↗
PubMed1996

Differentiation of alpha coma from awake alpha by nonlinear dynamics of electroencephalography.

The electroencephalogram, as a probe of scalp-recorded electrical activity arising from the human cortex, provides useful information because of its temporal and spatial organization. Recent developments in nonlinear dynamics suggest that an object can be constructed in an n-dimensional space out of a temporal sequence of data such as an EEG signal and that its organization is characterized by the dimensionality of the object (in this case, human brain activity). We have carried out an analysis of a set of alpha coma EEG patterns in comparison to the awake alpha EEG patterns of normal volunteers and patients. Alpha coma recorded from a single channel is visually indistinguishable from normal resting alpha due to its similar frequency spectrum (a broad-band spectrum with 1/f characteristics). Our results show that alpha coma dimensionality, however, differs from that of normal alpha in that it has a greater variability over different temporal segments of EEG. Single channel recordings in 7 patients with alpha coma were differentiable from those of 10 subjects with "normal" EEGs. Through dynamic analysis of the EEG, novel methods of signal extraction from EEG may become evident and applicable to clinical practice.

Adult↗
PubMed1995

Electroencephalography in lacunar infarction.

To determine the occurrence and clinical implications of electroencephalographic (EEG) abnormalities in patients with acute lacunar infarction, we conducted a single-blinded EEG study in 55 patients. Twenty-nine (53%) had mild EEG abnormalities, which were focal and ipsilateral to the side of infarction in 7 patients (13%). Abnormalities were more common in patients with evidence of a prior stroke (10 of 12 patients, 83%). However, 43% (16 of 37 patients) of those without historical or radiologic evidence of a prior stroke also had mild EEG abnormalities. This represents a higher incidence of routine EEG abnormalities in lacunar infarction than is generally assumed. Indeed, these findings are more consistent with recent quantitative EEG studies that consistently have shown high rates of abnormalities in lacunar infarction. We did not find major EEG abnormalities, such as continuous or nearly continuous focal delta activity, in any patient with first lacunar infarction. We conclude that within the first 48 h after a first ischemic infarction, when computed tomography often fails to show abnormalities, an EEG that shows lateralized major abnormalities is useful in excluding the diagnosis of either lacunar infarction or infarction limited to the brain stem. Mild abnormalities occur more often than previously thought in lacunar infarction and do not exclude this diagnosis.

Aged↗
PubMed1992

Processing asymmetries for complex sounds: comparisons between behavioral ear advantages and electrophysiological asymmetries based on quantitative electroencephalography.

This experiment extends our earlier work on individual differences in ear advantages for complex sounds (Lauter 1982, 1983, 1984) to examine the results of combined behavioral and qEEG testing in the same subjects. Results include: (1) between-subject differences in absolute values together with between-subject agreements in terms of relative values, observed both for ear advantages (EAs) and hemisphere advantages (HAs); (2) within-subject agreement between behavioral (EAs) and physiological (HAs) measures of asymmetries; and (3) preliminary findings related to the interpretation of qEEG asymmetry data, such as the influence of hand movements on auditory-cortex qEEG recordings, and persistence of activation effects in which asymmetries evoked during a stimulation condition may be reflected in resting asymmetries observed during a subsequent control condition.

Acoustic Stimulation↗
PubMed1980

The value of electroencephalography in prolonged coma: a comparative EEG-computed axial tomography study of two patients one year after trauma.

Interest was aroused in two patients of 16 and 17 years of age and similar craniocerebral trauma, but who had differing EEG's 1 year after injury while their later situation was the reverse of what the EEG would have led one to expect. The patient with an iso-electric EEG showed clinical improvement during the course of the second year, as indicated by a rise in his Glasgow coma rating from 8 to 11. This patient had marked cortical atrophy with discrete central atrophy, shown by computed axial tomography (CT); the isotope cisternogram showed good peripheral absorption of the isotope and no penetration into the ventricles. The other patient showed diffuse slow-wave activity in his EEG but failed to improve clinically or electroencephalographically. His CT-scan showed marked central and discrete cortical atrophy; his isotopic cisternogram showed penetration of isotope into the ventricles with poor peripheral absorption. These two cases illustrate the hazard of relying on an iso-electric EEG after 1 year of coma as an indicator of brain death, and the value of the CT-scan in the initial assessment of such cases.

Adolescent↗
PubMed1996

Introducing spatio-temporal reasoning into the inverse problem in electroencephalography.

Studying the Brain's Electrical and Magnetic Signals (BEMS) requires the contribution of many area of research that include anatomy, neurophysiology and electromagnetic theory. NEUROLAB is a framework dedicated to the study of brain disorders. Upon completion, it should provide users with an intelligent computational environment that incorporates qualitative and quantitative models of the brain and head, and a model for representing and reasoning about time and space. Spatio-temporal knowledge of a given problem is represented as a constraint network where to each node of the network are attached temporal and spatial variables that must satisfy the constraints defined by the arch labels connecting the nodes. In this paper, we show how temporal reasoning can be combined with spatial descriptions to produce different scenarios of possible seizure spread. These scenarios can provide a priori information for the inverse problem the role of which is to localise the sources of the observed BEMS.

Artificial Intelligence↗
PubMedDate not supplied

Estimating anesthetic depth by electroencephalography during anesthetic induction and intubation in patients undergoing cardiac surgery.

Intravenous (IV) anesthesia titrated to continuous computer-processed electroencephalograms (EEGs) was studied in 32 consecutive patients undergoing cardiac surgery. Anesthesia was induced with fentanyl 50 micrograms/kg with no EEG monitoring (n = 16) or 25 to 50 micrograms depending on changes in EEG (n = 16). EEG, oxygen saturation by pulse oximeter, intra-arterial blood pressure (BP), central venous pressure (CVP), and pulmonary artery pressure (PAP) (n = 18) were monitored continuously. Cardiac output (CO), CVP, PAP, spectral-edge frequency for each hemisphere, and BP were recorded before induction, immediately before intubation, and 1 and 5 minutes after intubation. With EEG monitoring, intubation was performed when spectral-edge frequency decreased to 10 Hz or less. Recall and pain were investigated 2 to 12 weeks postoperatively. With EEG, the amount of fentanyl used before intubation was significantly lower (39.7 +/- 2 micrograms/kg; p less than 0.005) than without EEG (50 micrograms/kg). The decrease in BP (% change) was less with than without EEG; mean changes in BP between preinduction and preintubation were -7.4% +/- 3.8% and -16.5% +/- 3.1% and between preinduction and 1 minute after intubation 0.3% +/- 3.4% and -12.5% +/- 3.5%, respectively. Percent changes in mean BP between intubation and 1 minute after were 9.6% +/- 4.0% with EEG and 5.2% +/- 3.0% without EEG. No patient in either group had recall. The authors conclude that using EEG monitoring to estimate depth of anesthesia during induction and laryngoscopy may increase safety in high-risk patients undergoing cardiac surgery.

Adult↗
PubMedDate not supplied

Cerebral hemodynamic changes and electroencephalography during carotid endarterectomy.

Some patients undergoing endarterectomy for occlusive carotid artery disease run a risk of brain ischemia during cross-clamping of the artery. The present study of 15 patients was undertaken to evaluate changes in cerebral blood flow (CBF), as measured with an intravenous (IV) tracer (133Xenon) technique, and to relate CBF changes to changes in the electroencephalogram (EEG). CBF was measured before and after induction of anesthesia, during cross-clamping of the carotid artery, after release of the clamps, and at 24 hours after the operation. All the patients were anesthetized with methohexitone, fentanyl, and nitrous oxide and oxygen. EEG was continuously recorded during the operation. Carotid artery shunts were not used. In 8 patients, cross-clamping of the carotid artery did not influence the EEG. In this group of patients, induction of anesthesia caused a 38% decrease in CBF, which presumably reflects the normal reaction to the anesthetic agent given. There were no further changes in CBF during cross-clamping. In 7 patients, the EEG showed signs of deterioration during the intraoperative vascular occlusion. In these patients, anesthesia did not cause any CBF change, whereas cross-clamping the artery induced a 33% decrease in CBF. In individual patients, the severity of EEG changes correlated with the decrease in CBF. The absence of a change in CBF by anesthesia and a decrease due to cross-clamping of the carotid artery may be explained by the presence of a more advanced cerebrovascular disease and an insufficiency to maintain CBF during cross-clamping.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2006

The novelty value of the combined use of electroencephalography and transcranial magnetic stimulation for neuroscience research.

Electroencephalographic (EEG) responses measured simultaneously with transcranial magnetic stimulation (TMS) have opened a new window into the human nervous system. The combined use of TMS and EEG (TMS-EEG) provides a means for the detailed study of the reactivity of any cortical region in the intact brain; also the reactivities of non-motor cortical areas related with higher-order functions are now appreciable. A recent epochal finding concerning cortical reactivity is that neuronal activation is induced with remarkably low stimulation intensities. This knowledge is significant when optimizing experimental set-ups for maximal patient safety. Stimulation of different cortical areas evokes different patterns of remote EEG activity, confirming the viability of TMS-EEG for the study of corticocortical connections. In this review, we expand on these and other notable findings related with TMS-EEG. We discuss the possibilities of the technique for the study of cortical reactivity and connectivity. We show that TMS-EEG allows the study of interhemispheric connections with high spatiotemporal specificity and the assessment of cortical reactivity with excellent sensitivity.

Biomedical Research↗
PubMed2005

The role of quantitative electroencephalography in child and adolescent psychiatric disorders.

This article presents a critical review of quantitative electroencephalographic (qEEG) research and issues relevant to its clinical application. Included is a summary of methodologic issues necessary for a reliable implementation of qEEG within clinical settings and a brief discussion of controversial issues surrounding this implementation. The main body of the article includes a summary of qEEG findings that involves adults with various neurologic and psychiatric disorders, which is followed by an in-depth presentation of qEEG research that involves children and adolescents with neurologic and psychiatric disorders. A concluding section presents a qEEG-based neurophysiologic model of attention deficit disorder.

Adolescent↗
PubMed2004

Magnetoencephalographic spikes not detected by conventional electroencephalography.

OBJECTIVE: To investigate some of the reasons why magnetoencephalographic (MEG) spikes are at times not apparent in conventional electroencephalograms (EEG) when the data are co-registered, and to explore to what extent modern EEG analysis methods can improve the yield. METHODS: Seventy seconds of MEG-EEG co-registration on a 122 channel Neuromag system were studied in a 10-year-old boy with Landau-Kleffner syndrome. Twenty-six EEG channels were originally recorded with a left ear reference. The EEG data were subsequently reformatted (BESA) to a variety of montages for the 10-20 and 10-10 electrode array. A 10 s data epoch was compared in detail for concordance between MEG and EEG spikes. To detect the characteristics of hidden low voltage EEG spikes, MEG spikes were averaged and compared with the concomitant averaged EEG spike. RESULTS: While there was an abundance of EEG as well as MEG spikes on the left; definite right-sided spikes were not visible in the EEG. Right hemispheric MEG spikes were, however, plentiful with an average strength of 757 fT. When the individual MEG spikes from the right hemisphere were compared with the corresponding EEG events their amplitude ranged between 24 and 31 microV and were, therefore, indistinguishable from background activity. The majority of them became visible, however, with further sophisticated data analysis. CONCLUSIONS: When the relative merits of MEG versus EEG recordings for the detection of epileptogenic spike are investigated the 10-20 system of electrode placement and conventional methods of EEG analysis do not provide optimal data assessment. The use of the 10-10 electrode array combined with modern methods of digital data analysis can provide better concordance with MEG data.

Child↗