Topographic electroencephalographic study of transient ischemic attacks

Neuroprotection assessment by topographic electroencephalographic analysis: effects of a sodium channel blocker to reduce polymorphic delta activity following ischaemic brain injury in rats

The spatiotemporal electroencephalogram (EEG) pathology associated with brain injury was studied using high-resolution, 10-electrode cortical EEG mapping in a rat model of middle cerebral artery occlusion (MCAo). Using this model we evaluated the ability of the novel sodium channel blocker and neuroprotective agent RS100642 to resolve injury-induced EEG abnormalities as a measure of neurophysiological recovery from brain injury. The middle cerebral artery (MCA) was occluded for 1 h during which a dramatic loss of EEG power was measured over the injured cortex with near complete recovery upon reperfusion of blood to the MCA region in all rats. The resultant progression of the MCAo/reperfusion injury (6-72 h) included the appearance of diffuse polymorphic delta activity (PDA), as visually indicated by the presence of high-amplitude slow-waves recorded from both brain hemispheres. PDA was associated with large increases in EEG power, particularly evident in outer 'peri-infarct' regions of the ipsilateral parietal cortex as visualized using topographic EEG mapping. Post-injury treatment with RS100642 (1.0 mg/kg, i.v.) significantly reduced the PDA activity and attenuated the increase in EEG power throughout the course of the injury. These effects were associated with a reduction in brain infarct volume and improved neurological function. These methods of EEG analysis may be helpful tools to evaluate the physiological recovery of the brain from injury in humans following treatment with an experimental neuroprotective compound.

Quantitative electroencephalography spectral analysis and topographic mapping in a rat model of middle cerebral artery occlusion

Electroencephalography (EEG) has a long history in clinical evaluations of cerebrovascular disease. Distinct EEG abnormalities, such as increased slow delta activity, voltage depression and epileptiform discharge, have been identified in stroke patients. However, preclinical use of EEG analysis of cerebral ischaemia is less documented. We report a new rat model of EEG topographic mapping during permanent and transient middle cerebral artery occlusion. Ten EEG electrodes were implanted on the rat skull, symmetrically covering the cortical regions of two hemispheres. Monopolar EEG recordings were acquired from each animal at multiple time points during the initial 24 h, and again once daily for 7 days. Traditional EEG examinations, quantitative EEG (qEEG) spectral analysis and topographic EEG mapping were employed for comprehensive data analyses. Several distinct spatiotemporal EEG abnormalities were identified in the ischaemic rat brain. In the ipsilateral hemisphere, pronounced increase in delta activity was observed in each recorded area within 24 h of injury. While sharp waves and spike complexes dominated the parietal region, a nearly isoelectric EEG state was seen in the temporal region. After 48 h, spontaneous, albeit incomplete, recovery of EEG activities developed in all rats. Reperfusion appeared to promote delta and alpha recovery more efficiently. The contralateral EEG changes were also recorded in two phases: an acute moderate increase in delta activities with intermittent rhythmic activities, followed by a delayed and significant increase in beta activities across the hemisphere. The similarities of rat qEEG profiles identified in this study to that of stroke patients and the application of topographic mapping broaden our research technology for preclinical experimental studies of brain injury.

[Guidelines for recording/analyzing quantitative EEG and evoked potentials. Part II: Clinical aspects]

Digital EEG (DEEG) and quantitative EEG (QEEG) are recently developed tools present in many clinical situations. Besides showing didactic and research utility, they may also have a clinical role. Although a considerable amount of scientific literature has been published related to QEEG, many controversies still subsist regarding its clinical utilization. Clinical applications are: 1. DEEG is already an established substitute for conventional EEG, representing a clear technical advance. 2. Certain QEEG techniques are an established addition to DEEG for: 2a) screening for epileptic spikes or seizures in long-term recordings; 2b) Operation room and intensive care unit EEG monitoring. 3. Certain QEEG techniques are considered possible useful additions to DEEG: 3a) topographic voltage and dipole analysis in epilepsy evaluations; 3b) frequency analysis in cerebrovascular disease and dementia, mostly when other tests have been inconclusive. 4. QEEG remains investigational for clinical use in postconcussion syndrome, learning disability, attention disorders, schizophrenia, depression, alcoholism and drug abuse. EEG brain mapping and other QEEG techniques should be clinically used only by physicians highly skilled in clinical EEG interpretation and as an adjunct to traditional EEG work.

Assessing the accuracy of topographic EEG mapping for determining local brain function

OBJECTIVE

There has been considerable discussion regarding the accuracy of topographic electroencephalographic (EEG) maps for assessing local cerebral function. We performed this study to test the accuracy of EEG mapping by examining the association between electrical activity and the perfusion under each electrode as another measure of local cerebral function.

METHODS

EEG mapping was performed simultaneously with (H15)2O positron emission tomography (PET) scanning in 6 normal adult subjects, both at rest and during a simple motor task. EEG data were processed using 3 different montages; two EEG power measures (absolute and relative power) were examined.

RESULTS

Relative power had much stronger associations with perfusion than did absolute power. In addition, calculating power for bipolar electrode pairs and averaging power over electrode pairs sharing a common electrode yielded stronger associations with perfusion than data from referential or single source montages.

CONCLUSIONS

These findings indicate (1) that topographic EEG mapping can accurately reflect local brain function in a way that is comparable to other methods, and (2) that the choice of EEG measure and montage have a significant influence on the degree with which maps reflect this local activity and function.

Evaluation of cerebral function after carotid endarterectomy

Neuroimaging methods have failed to disclose correlation between degree of cerebral atrophy and blood flow in carotid artery stenosis patients. Moreover, intellectual improvement after carotid endarterectomy does not correlate fully with neuroimaging data in such patients. We performed brain electrical activity mapping and psychological testing before and 4 weeks after operation in 28 patients with symptomatic, high-grade, carotid stenosis. Postoperatively, electroencephalographic (EEG) mean frequency and absolute theta power improved significantly (p < 0.01). Mean frequency increased >1 Hz in most areas while power decreased dramatically, mainly because of resolution of high-voltage foci in 8 patients. Differences were conspicuous in both frontal lobes irrespective of the operated side, which suggests changes in perfusion affecting the whole brain. This is a positive effect of endarterectomy. Mini-Mental test and Set Test for verbal fluency had a positive correlation with the qEEG changes. Quantitative EEG as a measure of cerebral function has disclosed discriminative improvement in the early postoperative period. Our results support the thesis of improvement subsequent to endarterectomy.

Quantitative EEG analysis in clinical settings

Quantitative EEG techniques are becoming more available. Eventually, all EEG will be digital. Various digital utility programs can help even now with storage and viewing the polygraph EEG itself. Techniques of frequency analysis, topographic mapping and discriminant functions are also available but have limited clinical use. Applications as a monitoring tool and careful analysis of epileptic spikes have been shown some promise but need further study to identify their proper clinical roles.

Sources of spontaneous slow waves associated with brain lesions, localized by using the MEG

Electric or magnetic slow wave brain activity can be associated with brain lesions. For an accurate source localization we transformed the magnetoencephalographic (MEG) coordinate system to the magnetic resonance imaging (MRI) system by using a surface fit of the digitally measured head surface and the reconstructed surface of the MRI scan. Furthermore we solved the problem to separate sources of focal activity from other multiple sources by introducing a spatial average, the Dipole Density Plot (DDP). The DDP shows in a quantified manner concentrations of dipoles across time. The DDP uses the single dipole model adequately, because only those signal sections will be analyzed, where one component contributes to the signal predominantly. In all cases, where multiple sources concurrently active are to be localized, a current distribution analysis will be used, the Current Localization by Spatial Filtering (CLSF). All source localization procedures were tested using structural brain lesions, which were verified by imaging techniques (MRI or CT), showing the results in close topographical relation to the lesions. The results so far let us assume, that the DDP and the CLSF are valuable tools to localize sources of focal spontaneous slow wave electrical brain activity.

Preoperative cerebrovascular symptoms and electroencephalographic abnormalities do not predict cerebral ischemia during carotid endarterectomy

BACKGROUND AND PURPOSE

The purpose of this prospective study was to establish (1) whether patients with neurological symptoms scheduled for carotid endarterectomy had an increased incidence of electroencephalographic (EEG) abnormalities during awake baseline recordings, (2) whether these symptoms and EEG abnormalities predicted ischemic EEG pattern changes at carotid artery cross-clamp, and (3) whether there was an association between age, presence of EEG baseline abnormalities, and ischemic pattern changes at carotid artery cross-clamp.

METHODS

We reviewed the medical record of each patient scheduled to undergo carotid endarterectomy and recorded the patient's age and history of previous neurological symptoms. We then continuously monitored and analyzed 16 channels of anteroposterior bipolar EEG and two of referential derivations from at least 5 minutes before induction of anesthesia and throughout the operation.

RESULTS

We completed 394 consecutive studies. Preoperative neurological symptoms were related to EEG abnormalities in awake patients (P < .001) and to EEG asymmetries in anesthetized patients (P < .001). Abnormal awake EEG findings were associated with asymmetries after anesthesia (P < .0001). Twenty-eight percent of both symptomatic (70/249) and asymptomatic (41/145) patients had EEG ischemic pattern changes at carotid artery cross-clamp. Neither neurological symptoms nor EEG abnormalities were associated with age or the development of EEG ischemic pattern changes at carotid artery cross-clamp.

CONCLUSIONS

Despite the strong association between a history of cerebral ischemic symptoms and preoperative EEG abnormalities in patients undergoing carotid endarterectomy, patients who have suffered strokes or transient ischemic events are at no greater risk of having EEG evidence of cerebral ischemia during carotid artery cross-clamp than patients without symptoms and with normal baseline EEGs. We conclude that preoperative EEG abnormalities in symptomatic patients are not due to age or to insufficiency of regional cerebral blood flow.

Mapeamento Cerebral

O mapeamento cerebral é uma técnica digital que gera mapas topográficos coloridos da atividade eletrencefalográfica captada sobre o escalpo. O eletrencefalograma após passar por um microcomputador, que realiza a análise quantitativa em várias faixas de freqüência, pode ser visualizado em um monitor colorido (EEG digital). Posteriormente, as épocas do EEG digital são selecionadas para a realização dos mapas, impressão final e arquivo em disquetes. Este método tem demonstrado ser ON em várias doenças neurológicas e psiquiátricas e deve ser realizado sempre em conjunto com o EEG digital. Achamos que dentro de alguns anos os aparelhos de EEG digital/mapeamento cerebral substituam as máquinas que realizam o EEG convencional.

Symptomatic and asymptomatic high-grade unilateral internal carotid artery stenosis: scalp topography of event-related potentials (P300) and psychometric testing

Unilateral internal carotid artery (ICA) stenosis may be accompanied by widespread atherosclerosis of extra- and intracranial vessels leading to subtle cognitive disorders. We applied multichannel recording of P300 in 28 patients (68.3 +/- 8.1 years; 15 asymptomatic, 13 with a history of transient ischemic attack (TIA)) and compared them with an age- and sex-matched control group. All underwent a visual "odd-ball paradigm" as well as a psychometric test, the Cognitive Performance Test (CPT), testing mainly visual attention and memory. The potentials were derived from 16 electrodes according to the 10/20 system against linked mastoids. The latencies and amplitudes of N250 and P300 were measured and their amplitudes additionally mapped. Furthermore, the early sensory exogenous potentials, P1 and N1, within the P300 potentials as well as conventional pattern reversal visual evoked potentials (PVEPs) were evaluated. (1) Both the early exogenous potentials and the conventional PVEPs showed no significant differences among all groups. (2) There were no significant differences between asymptomatic patients and those with a TIA history in all parameters of the P300 complex so that one total patient group was constructed and compared to the controls. (3) Patients' P300 amplitudes showed significant reductions over hemispheres ipsilateral (P < or = 0.014) and contralateral (P < or = 0.044) to the stenosis. (4) The N250 amplitudes were reduced only in the central leads (P < or = 0.05). (5) The latencies of N250 potentials were significantly prolonged at many electrodes, not only ipsi-(P < or = 0.0007) but also contralateral (P < or = 0.022) to the stenosis. (6) The patients' P300 latencies showed significant lengthening only at occipital sites (P < or = 0.05) compared to controls. (7) In all measured parameters, within the patient group, the differences between hemispheres ipsilateral versus contralateral to the ICA stenoses did not reach statistical significance. (8) The CPT values detected slight cognitive disorders for both patient groups and they correlated significantly with the latencies in many leads. (9) The highest test sensitivity to classify patients versus controls (z score > 2) was reached in P300 maps of TIA patients (77%). An altered P300 indicates electrophysiologically, and CPT behaviorally, subclinical cognitive deficits even in asymptomatic patients with unilateral tight ICA stenoses. Interestingly, no differences between asymptomatic and TIA patients with a high-grade unilateral ICA stenosis could be found.

Status of quantitative EEG (QEEG) in clinical practice, 1994

Clinical quantitative EEG (qEEG) is a complex specialty that may include not only standard EEG but also digital ("paperless") EEG, topographic mapping, spectral analysis, spectral coherence, long latency and event related potentials (EP), significance probability mapping (SPM), dipole source localization methodology (DLM), and discriminant function analysis. There are three basic clinical uses: non-specific detection of organicity/encephalopathy, specific categorization of disease or clinical condition, and epileptic source localization. Extreme variations exist in the competency of laboratories practicing clinical qEEG; universally agreed upon standards of practice have not been established but there are a number of efforts to do so. As expected, the clinical value of qEEG to patients varies similarly. Criticisms of qEEG have now been answered: Color displays need not be deceptive. Statistical "capitalization upon chance" can be easily avoided. By training and with newer analytic procedures, artifacts can be recognized and often removed. Data based upon spectral analysis and EP can reliably classify clinical conditions thereby demonstrating a greater sensitivity to EEG/EP data than possible by conventional visual inspection. QEEG is clearly of clinical value when performed in concert with standard EEG and analyzed by clinicians with demonstrated competency in standard EEG followed by specialized training and demonstrated competency in qEEG. QEEG is not a simple substitute for conventional EEG and cannot be seen as a substitute for clinical competence. Although continuing to develop, qEEG technology has matured sufficiently and is now well established. Concerns regarding its clinical use have primarily resulted from its misapplication and misinterpretation stemming, largely, from inadequate personnel training and expertise.

Computerized electroencephalographic assessment of congenital brain infarction

We studied 12 children (8 female and 4 male) aged 2.2-14.3 years, whose computed tomographic (CT) examination had shown evidence of malacic and/or porencephalic outcomes of early vascular brain infarction. Topographic spectral electroencephalographic (EEG) analysis was performed in all patients in the awake state. The following spectral EEG variables were studied: topography, absolute and relative power of delta, theta, alpha, beta bands, overall power, and peak alpha frequency asymmetries. The results of topographic spectral EEG analysis were compared with the localization and nature of lesions as detected by CT scans. Depending on the nature of the lesions, we were able to identify two different spectral patterns. Porencephalic cysts were characterized by an increase in delta and theta bands in the areas surrounding the lesion sites, as identified by CT. Spectral EEG patterns of malacic outcomes resulted in a focal increase in theta and delta band power, corresponding to the topography of lesions. Moreover, in 9/12 subjects an asymmetry of alpha rhythm in occipital leads was found homolaterally to the lesion sites, associated with a decrease in power, without any CT evidence of an occipital lesion.

A comparison of quantitative electroencephalography, computed tomography, and behavioral evaluations to localize impairment in patients with stroke and transient ischemic attacks

Brain computed tomography and a structured behavioral assessment provided a better correlation than did quantitative electroencephalography to the presence of mild stroke or transient ischemic attacks in 21 patients. When electroencephalography did not correlate well, it tended to localize too laterally or miss deep lesions. Computed tomography did not identify 2 lesions when done early after disease onset. No test was uniformly more sensitive or accurate than others. They may complement each other.

EEG mapping in middle aged normal volunteers: the impact of cerebrovascular risk factors

The impact of major risk factors for stroke on EEG mapping and routine EEG findings was evaluated in volunteers with no clinical signs of cerebrovascular or other neuropsychiatric disease. Focal changes were seen in 22 subjects (30%) by means of EEG mapping, but in only 12 cases (16%) when routine-EEG was used (p < .05). 4/35 (11%) volunteers without RF had focal changes while this was seen in 18/39 (46%) subjects in whom risk factors (RF) were found (p < .01). An association was seen between the presence of EEG foci and number of RF. 59% of subjects with 2 or 3 RF had focal abnormalities as opposed to 36% of those with 1 RF and 11% of RF free individuals (p < .05). The findings could be confirmed by averaging the EEG data according to the different number of RF revealing statistically significant differences between each of the 3 groups. Using routine EEG alone no significant correlation to the presence or number of RF was found. Our data demonstrate EEG abnormalities in a considerable portion of normal middle aged individuals which in part may be attributed to the presence of RF.

Transient ischemic attacks: electrophysiological (conventional and topographic EEG) and radiological (CCT) evaluation

The value of electrophysiological tests: conventional electroencephalography (EEG), topographic EEG analysis as well as computerized tomography (CT) in the diagnosis and evaluation of 25 patients with manifestations of transient ischemic attacks (TIA) in the domain of the carotid system was assessed. Normal CT was the rule in TIA patients except in 8% of the cases, where nonspecific changes of brain atrophy were described. Conventional EEG, topographic EEG and spectral analysis could detect abnormalities in 48%, 80% and 64% of TIA cases respectively. None of the abnormal EEG records could be missed by topographic EEG analysis. 32% of the records were diagnosed as abnormal by topographic EEG, while conventional EEG failed to detect abnormalities. Spectral analysis of the EEG results revealed a significant decrease regarding mean high limit alpha percent power, and a significant increase regarding mean low and high limit theta percent power, as well as a significant increase of the mean high limit of the slow activities (delta + theta)/fast activities (alpha + beta) percent power ratio in the TIA group as compared to the normal control group.

Current role of electroencephalography in cerebral ischemia

BACKGROUND

The electroencephalogram has been largely supplanted by neuroimaging techniques for the diagnosis and localization of ischemic stroke. However, because of its close correlation with cerebral metabolism and its ability to detect brief transient alterations in cortical function, the electroencephalogram may still be useful for certain diagnostic applications in stroke.

SUMMARY OF REVIEW

The relation of electroencephalographic phenomena to cerebral blood flow and metabolism is reviewed. Ten clinical questions that can be addressed by the electroencephalogram in patients with stroke are posed. The presence of seizures, confirmation of diagnosis, intraoperative monitoring, and level of consciousness are areas of proven usefulness. The electroencephalogram provides less worthwhile information about the time course, prognosis, and localization of strokes. Computerized techniques are of potential but unproven value.

CONCLUSIONS

The electroencephalogram retains a worthwhile place in the evaluation of patients with cerebral ischemia when it is used to answer specific questions. All patients with strokes do not need electroencephalograms, but the test can provide uniquely useful data in some.

The EEG mapping in the evaluation of patients with late onset epilepsy

In 62 patients with late onset epilepsy the findings of EEG mapping routine EEG and CT were compared. Forty four patients had generalized, 18 partial seizures. In 39 patients (63%) EEG mapping revealed focal changes but only in 24 patients (39%) using routine EEG alone. Thus the EEG mapping showed focal abnormalities significantly more often and this could be demonstrated in the separated groups of patients with generalized or partial seizures as well. Lesions in CT occurred in 39 patients (63%). The focal abnormalities in EEG mapping were significantly related to the lesions in CT. Moreover focal changes corresponding to CT lesions were obtained by means of EEG mapping in 32 patients (82%) but only in 20 patients (51%) using routine EEG and in that way the EEG mapping could indicate focal lesions in CT significantly more often than routine EEG. Regarding etiology this was especially seen in the group with vascular origin of epilepsy.

The value of EEG-mapping in focal cerebral lesions

In 148 patients with focal cerebral lesions the findings of EEG mapping, routine EEG and CT were compared. Regarding etiology 43 patients suffered from completed stroke (CS), 43 patients from transient ischemic attack (TIA), 33 patients had an intracerebral hemorrhage (ICH) and 29 an hemispheric tumor. In 37 patients with CS (86%) and 27 patients with TIA (63%) the EEG mapping revealed focal changes, but only in 28 patients with CS (65%) and in 11 patients (26%) with TIA using routine EEG alone. Thus the EEG mapping showed focal abnormalities significantly more often. In the remaining patient groups no significant difference in the results of EEG mapping or routine EEG could be demonstrated. Focal abnormalities corresponding to focal lesions seen in CT were obtained by means of EEG mapping in 27 patients (90%) with CS and 10 patients (77%) with TIA, but only in 17 patients (57%) with CS and 4 patients (31%) with TIA using routine EEG and in that way the EEG mapping could indicate focal lesions in CT significantly more often than routine EEG. In the remaining patient groups no significant difference in the number of focal changes corresponding to lesions in CT could be seen.

Quantitative EEG monitoring for patients with subarachnoid hemorrhage

We evaluated the sensitivity of continuous quantitative EEG in 11 patients with subarachnoid hemorrhage (SAH). We correlated compressed spectral array (CSA) and trend analysis (TA) of total power (1-30 Hz), frequency centroid (1-30 Hz), alpha ratio and percent delta power with clinical and radiological findings. For all ischemic events (n = 11), the most sensitive TA parameter was a change in total power (91%), followed by changes in alpha ratio (64%), frequency centroid (55%), and percent delta (45%). Comparable CSA features were changes in power (44%) and slowing (39%). Total power and frequency varied independently. In 4 cases, EEG findings on TA appeared before clinical changes. Continuous quantitative EEG may be useful for monitoring and predicting ischemia following SAH. TA of individual EEG parameters is more sensitive than CSA, and total power is the most sensitive.

EEG mapping applications in psychiatric disorders

A number of techniques have been developed for EEG mapping in recent years. The clinical and research applications of these techniques in psychiatry are reviewed with regard to schizophrenia, affective disorder, learning disorders, dementia, psychopharmacology and ruling out neurological disorders. Limitations and advantages of EEG mapping as well as its relation to other imaging techniques are discussed.

Inter- versus intra-subject variance in topographic mapping of the electroencephalogram

The variability of the normal topographic EEG distribution between a quiet, eyes closed, resting state and the performance of cognitive tasks (listening to a story or music) was studied in 20 normal (10 male) right-handed college students or graduates ages 18-40 yrs. Amplitude changes in the topographic frequency distribution (2.5-7 SD) of alpha frequency band (8-13 Hz) were noted between tasks and resting state in individual subjects. When group data for the resting versus listening states were compared, no statistical differences could be demonstrated. The group variability was 50% of the power of the resting record. Repeat studies in 10 subjects demonstrated a test-retest variance of 10% of the mean individual power. The data suggest that inter-subject differences in the alpha frequency and individual topographic differences will require careful normalization for development of baseline "brain maps" to serve as a standard for investigation of disease states.

Computed EEG topography in acute stroke

The potential for clinical application of computed EEG topography (CET) has been known since 1978. However, studies relating to the focal brain lesions are few. We have studied 19 cases of acute stroke involving the cerebral hemispheres. CET and EEG were recorded as soon as possible, usually within 1-3 days of onset. Repeat maps were recorded at 1 wk. Symptoms, neurologic exam, routine EEG and CT scan were compared with the CET of power spectral and flash evoked potential data. Statistical criteria were also applied. Good correlation was noted between CET and EEG and CT. Occasionally, CET was noted to provide information beyond EEG or CT. These early studies suggest a potential utility for CET in the early diagnosis of stroke.

Topographic EEG mapping in cerebrovascular disease

Topographic EEG based on the power spectral data were correlated with cortical CBF and CMRO2 which were provided by positron emission tomography (PET) in patients with cerebral infarction. Delta and theta activities correlated negatively with CBF and CMRO2 whereas alpha activity correlated positively. For delta activity, both absolute (AP) and relative power (RP) showed significant correlation with CBF and CMRO2. For alpha activity, RP showed closer correlation with CBF and CMRO2 than did AP. The z-scores for these power data also showed significant correlation with the PET data although the degree of correlations did not improved even with the z-score. Topographic EEG images including AP, RP and their z-score maps well corresponded with the PET images: z-score maps were considered to be useful tool in topographical extraction of the features of the EEG power data.

Electroencephalographic correlates of blood flow and oxygen metabolism provided by positron emission tomography in patients with cerebral infarction

Quantitative EEG data were analyzed statistically with respect to cortical cerebral blood flow (CBF) and oxygen metabolism (CMRO2) measured by positron emission tomography in 47 patients with unilateral cerebral infarction. Relative value of the square root of average power was used as a percentage power fraction (PPF) for each frequency category. Power ratio index (PRI) was calculated by dividing the combined delta-PPF and theta-PPF by the combined alpha-PPF and beta-PPF. Delta-PPF, theta-PPF and PRI correlated negatively with regional CBF (rCBF) and CMRO2 (rCMRO2) whereas alpha-PPF and beta-PPF correlated positively. In the acute stage, delta-PPF, alpha-PPF and PRI correlated with rCBF at all but the frontopolar region whereas the correlation with rCMRO2 was poor. Alpha-PPF and PRI correlated also with rCMRO2 in the frontal, central, parietal and occipital regions while delta-PPF correlated with rCBF only in the parietal and occipital regions in the subacute stage. In the chronic stage, all EEG quotients correlated significantly with both rCBF and CMRO2 in the central and parietal regions. In the frontopolar region, only the theta-PPF correlated with rCBF throughout. In the comparison of hemispheric mean values, the correlations were always closer for the affected hemisphere than for the contralateral hemisphere. Although hemispheric mean CBF and CMRO2 were significantly lower in patients with cortical infarcts on CT than in those with small subcortical infarcts, there was no significant difference in the EEG data between the 2 groups.

Clinical utility of topographic EEG brain mapping

Topographic EEG brain mapping was performed on 100 patients referred for both EEG and neuroimaging procedures. Topographic maps were abnormal in 78% of patients with stroke, 50% with head trauma and 100% of those with space occupying lesions (tumor, abscess or intracerebral hematoma). Of the patients with abnormal EEG maps 30% had either sole or better localization with mapping than routine EEG or neuroimaging procedures. In no cases were there false localizing abnormalities by EEG mapping. Topographic mapping appears to provide better detection of low amplitude slow activity not easily discernible by routine EEG. It also provides faithful correspondence with localization of many lesions on neuroimaging procedures, and at times distinguishes abnormalities not immediately definable by CT/MRI. Topographic EEG mapping is a valuable adjunct to routine EEG.

Topographic EEG in brain ischemia--correlation with blood flow and metabolism

A review is made of topographic EEG analyses in patients with brain ischemia. Features correlating EEG measures and vascular and metabolic studies are presented and discussed within the content of the stage of ischemia. Quantitative EEG data was found to provide useful information regarding the effects of brain ischemia.

Averaging, spatio-temporal mapping and dipole modelling of focal epileptic spikes

A computer-based technique is described for the acquisition, spatio-temporal mapping and dipole modelling of epileptic spike events. Spike acquisition is operator-controlled and subsequent data processing is performed off-line. Preliminary averaging and topographical display of wave forms provide complementary information on the spike field. The method promises to be a useful adjunct to conventional EEG in spike analysis.