Background Electroencephalographic Activity Research Articles

Avaliação do Eletroencefalograma de Amplitude Integrada em recém-nascidos maiores que 35 semanas de idade gestacional expostos ao crack e/ou cocaína no pré-natal

OBJECTIVE: To evaluate the findings of video aEEG/EEG brain monitoring in newborns of mothers who used cocaine and/or crack during pregnancy and to describe the epidemiological profile of these mothers and infants. METHODS: Descriptive prospective study carried out from August 2019 to February 2020. We included newborns with a gestational age = 35 weeks and a history of maternal use of crack or cocaine during pregnancy. Newborns underwent video aEEG/EEG monitoring for 24 hours in the first 48 hours of life. The assessment of neonatal abstinence syndrome was performed using the Finnegan Score. Demographic and clinical data were analyzed. The Intergrowth-21 curve was used to classify the anthropometric measurements described. Capurro and New-Ballard methods were standardized for determining gestational age in newborns. RESULTS: 12 newborns met the criteria; all scored from 0 to 7 according to the Finnigan score in the first 6 hours of life. In the 30th hour of life, 10 (91%) scored between 0 and 7 and 1 neonate between 8 and 11, considered altered with the need for treatment. At 72 hours of life, the 12 newborns evaluated had scores between 0 and 7. The background electroencephalographic activity pattern in the first 48 hours of life was continuous, with the presence of a sleep-wake cycle in all cases. CONCLUSIONS: Newborns of drug-using mothers may have an early maturation pattern on electroencephalographic assessment. More studies are needed to assess this relationship better.

Changes in background electroencephalographic activity in benign childhood epilepsy with centrotemporal spikes after oxcarbazepine treatment: a standardized low-resolution brain electromagnetic tomography (sLORETA) study

BackgroundSeveral neuroimaging studies have reported neurophysiological alterations in patients with benign childhood epilepsy with centrotemporal spikes (BCECTS). However, reported outcomes have been inconsistent, and the progression of these changes in the brain remains unresolved. Moreover, background electroencephalography (EEG) in cases of BCECTS has not been performed often.MethodsWe investigated background EEG activity changes after six months of oxcarbazepine treatment to better understand the neurophysiological alterations and progression that occur in BCECTS. In 18 children with BCECTS, non-parametric statistical analyses using standardized low resolution brain electromagnetic tomography (sLORETA) were performed to compare the current density distribution of four frequency bands (delta, theta, alpha, and beta) between untreated and treated conditions.ResultsBackground EEG activity for the delta frequency band was significantly decreased in the fronto-temporal and limbic regions of the left hemisphere after oxcarbazepine treatment (threshold log-F-ratio = ±2.729, P < 0.01). The maximum current density difference was found in the parahippocampal gyrus of the left limbic lobe (Montreal Neurological Institute coordinate [x, y, z = 25, − 20, − 10], Brodmann area 28) (log-F-ratio = 3.081, P < 0.01).ConclusionsOur results indicate the involvement of the fronto-temporal and limbic cortices in BCECTS, and limbic lobe involvement, including the parahippocampal gyrus, was noted. In addition to evidence of the involvement of the fronto-temporal and limbic cortices in BCECTS, this study also found that an antiepileptic drug could reduce the delta frequency activity of the background EEG in these regions.

Early Electroencephalographic Findings Correlate With Neurologic Outcome in Children Following Cardiac Arrest.

To determine the clinical and electroencephalographic findings associated with prognosis in nonneonate children following cardiac arrest. Retrospective observational study. PICU and cardiac ICU. Nonneonate children with a history of cardiac arrest more than 2 minutes. Electroencephalographic monitoring within 72 hours of return of spontaneous circulation. Clinical and features, neurophysiologic data, and Pediatric Cerebral Performance Category scores were collected. Electroencephalographic traces were reviewed in a blinded manner, all seizures and electroencephalographic findings noted, and the electroencephalography was scored at 1 hour, 24 hours, and continuous electroencephalographic end. Discrete data regarding specific characteristics of the electroencephalographic background and seizures were studied. Univariate and multivariate analyses were performed to identify associations between clinical variables, electroencephalographic findings, and Pediatric Cerebral Performance Category score at hospital discharge. Multivariate analysis of 73 children revealed duration of cardiac arrest less than 20 minutes or continuous electroencephalographic background activity within 12 hours postreturn of spontaneous circulation were associated with good short term neurologic outcome. Change in electroencephalographic background score over time and electroencephalographic data collected after the initial hour were not associated with outcome. Following pediatric cardiac arrest, an initially normal electroencephalography or generalized slowing of the electroencephalographic background was associated with good neurologic outcome at hospital discharge.

노년 여성의 신맥.조해 저주파 자극이 뇌파에 미치는 영향

목적 : 본 연구는 노년층의 여성에게 신맥(BL62), 조해(KI6)혈에 대한 저주파자극이 뇌파에 어떠한 영향을 미치는지 알아보고 뇌 기능을 개선하는데 비화학적이고 비침습적인 자극 방법의 후보로써 가능성을 탐구해보고자 실시된 탐색적 연구이다. 방법 : 31명의 건강한 여성 피험자(평균연령, 54.5세)를 대상으로 이중맹검 무작위배정 임상연구가 12세션동안 실시되었다. 시험군에서는 감지할 수 없는 최대의 저주파자극이 실시되었으며(평균전류량, <TEX>$0.04{\mu}A$</TEX>), 대조군에서는 거짓자극이 실시되었다. 결과분석을 위해 12세션을 전후로 배경뇌파가 측정되었다. 결과 : 12세션의 자극이 실시된 후 대조군에 비해 실험군의 알파파 상대값은 11채널에서 유의한 증가를 보였으며(p<0.05), 감마파의 상대값은 7채널에서, 세타파의 상대값은 10채널에서 유의한 감소를 보였다. 결론 : 발목관절에 있는 신맥(BL62), 조해(KI6)혈에 대한 저주파 자극은 노년의 여성의 뇌에 베타, 세타, 감마파의 감소를 일으키는 반면 알파파를 선택적으로 증가시켜 뇌를 안정시키는 효과가 있는 것으로 보인다. 이러한 결과는 저주파자극이 향후 스트레스와 관련된 인지 문제를 치료하는 비침습적이고 비화학적인 도구로써의 가능성을 제공할 수 있을 것으로 보이며, 그 기전에 대한 추가적 연구가 필요할 것으로 보인다. Objectives : This study aimed to investigate the general effects of low-frequency electrical stimulation of the ankle joint acupuncture points(BL62 and KI6) on the brain waves of elderly women as a pilot study to figure out the possibility of candidate non-invasive and non-chemical stimulation method for the enhancing the brain function. Methods : A randomized, controlled, double-blinded clinical trial was performed in 31 healthy women(mean age, 54.5 years) within a treatment duration of 12 sessions. In the experimental group, low-frequency electrical stimulation was applied using the maximum range of the individual insensible strength(mean current, <TEX>$0.04{\mu}A$</TEX>). The control group received sham stimulation. The background electroencephalographic activity was measured before and after the12 sessions. Results : After 12 sessions of stimulation, the relative power of the alpha wave increased(32 of 32 channels: significant difference in 11 channels, p<0.05); the theta(30 of 32 channels: significant difference in 10 channels, p<0.05), beta(31 of 32 channels), and gamma(30 of 32 channels: significant difference in 7 channels, p<0.05) powers were also decreased compared with the sham group. Conclusions : Electrical stimulation on the ankle joint acupuncture points(BL62 and KI6) seemed to stabilize the elderly women brain by inducing the alpha power and reducing beta, theta, and gamma powers. These results provide insight into the action mechanism of the stimulation and can assist the future developement of a non-invasive and non-chemical treatment technique for stressor related cognitive problems.

Changes in background electroencephalographic activity in patients with epilepsy and/without comorbid depression

PURPOSE: Depressive disorders are the most common interictal psychiatric comorbidity in epilepsy. Recent data highlights the possibility of a close bi-directional pathophysiological relationship between these two disorders. Early detection and treatment of interictal depressive disorder (DD) may significantly improve patients' quality of life. The aim of the present study was to compare recorded interictal electroencephalographic (EEG) data in patients with epilepsy with and without comorbid DD. MATERIAL AND METHODS: Forty patients with epilepsy were divided into two groups according to the presence/absence of comorbid DD. They were diagnosed by applying the International Classification of Diseases, Version 10 (ICD-10) diagnostic criteria. Evaluation on Hamilton Depression Rating Scale (HAM-D-17) supported the diagnosis. Nineteen-electrode electroencephalography (EEG) with spectral analysis of the power was recorded for each participant. Gender- and age-matched subjects comprised a control group. RESULTS: An increase in slow wave EEG activity in the frontal and temporal lobe as well as a decrease in sensory motor rhythm was found out in the group of patients with epilepsy and comorbid DD. No such findings were detected in the group of patients with epilepsy only. CONCLUSION: Atypical presentation of interictal DD is common in epilepsy. Comorbid depression remains unrecognized and untreated in a great proportion of patients. Detection of certain patterns of EEG changes may be useful as a screening tool for forwarding these patients to a further psychiatric evaluation. It can serve as a basis for applying alternative therapeutic methods such as the biofeedback method. Scripta Scientifica Medica 2013; 45(1): 48-51.

Sensory information processing may be neuroenergetically more demanding in migraine patients

Electrophysiological studies of stimulus-evoked brain activation suggest that sensory processing in migraine patients is abnormal between attacks. The main findings are increased amplitudes and decreased habituation of cortical evoked potentials. Recent findings in healthy individuals showed that evoked potentials result mainly from phase resetting of background electroencephalographic activity. We recorded single trial visual evoked potentials during repetitive visual stimulation in migraine patients and healthy controls and analyzed these in the frequency domain for amplitude and phase. Increases in visual evoked potential amplitudes in migraine patients are explained almost entirely by increases in local amplitude, rather than increases in phase synchrony across trials. As amplitude modulation is generally considered more energy demanding than phase synchronization, this may explain the increased vulnerability of migraine patients to sensory stressors and the effectiveness of drugs that reduce evoked potential amplitudes or enhance aerobic energy metabolism.

Significance of background activity and positive sharp waves in neonatal electroencephalogram as prognostic of cerebral palsy

To study the significance of electroencephalographic background activity and positive sharp waves in neonatal electroencephalogram as prognostic of cerebral palsy. We studied prospectively and sequentially 73 newborns who had severe neonatal complications (neonatal anoxia, seizures, respiratory distress, sepsis, and meningitis). Nineteen newborns were excluded and 54 children formed the object of our study and were followed for 2 years. We analyzed gestational age, conceptional age, electroencephalographic background activity and positive sharp waves, which were correlated with cerebral palsy. There were no statistically significant correlation between gestational age and conceptional age and cerebral palsy; the electroencephalographic background activity was correlated with cerebral palsy as well as the positive sharp waves. Children with electroencephalographic background activity markedly abnormal and accompanied by positive sharp waves were associated with a worse prognosis.

Neurologic Aspects of MECP2 Gene Duplication in Male Patients

Duplications in Xq28 involving the methyl CpG binding protein 2 gene (MECP2) have been described in male patients with severe mental disability, delayed milestones, absence of language, hypotonia replaced by spasticity and retractions, and recurrent and often severe infections. In a study involving five patients in two families, multiplex ligation-dependent probe amplification was used to screen the Xq28 region that includes MECP2, focusing on the presence of gene duplications. Some manifestations of the disease observed in these patients may occur less regularly than the classical abnormalities. Epilepsy with frequent seizures of the myoclonic-astatic type was observed in these patients and was associated with a slowing of the background electroencephalographic activity, rather than the generalized spike-waves or polyspike-waves usually observed in this type of seizure. In addition, cerebral abnormalities were observed with magnetic resonance imaging that were inconstant and nonspecific but that could nonetheless assist in diagnosis of this genetic pathology.

Neonatal Seizures: Relation of Ictal Video-Electroencephalography (EEG) Findings With Neurodevelopmental Outcome

Neonatal electroencephalographic background activity has been found to be a predictive factor of the neurodevelopmental outcome. The aim of our study was to identify if the electrical ictal findings present on the first electroencephalography (EEG) recording are related to the outcome of newborns with neonatal seizures. The study is based on the prospective evaluation of newborns consecutively admitted to the Neonatal Intensive Care Unit at the University of Parma between September 2001 and September 2004. Thirty-eight subjects were enrolled in the study on the basis of the following inclusion criteria: presence on the first EEG of at least 1 seizure, neurodevelopmental follow-up until 18 months of corrected age, and performance of several ultrasound brain scans during the neonatal period and of at least 1 cerebral MRI within the first year of life. For each seizure, the following were considered: onset topography, morphology of the epileptiform discharges, spread of the discharge, number of electrographic regions of seizure onset, number of seizures per hour, duration of the seizures, and the Ictal Fraction (= total duration of the seizures/duration of the EEG recording x hour). At the last follow-up, the unfavorable neurodevelopmental outcome seems significantly related to the moderate/severe background activity abnormalities (p = .006), to the spread of ictal discharge to the contralateral hemisphere (p = .02), and to the Ictal Fraction, when it exceeds 10 minutes (p = .036). In conclusion, the analysis of the propagation of the ictal discharge and of the Ictal Fraction might suggest significant prognostic information since the first hours of life.

Electrical brain activity in preterm infants at risk for intracranial hemorrhage.

We studied the effect of preterm birth on electroencephalographic background activity in 20 infants < 32 weeks' gestation. Six infants developed periventricular-intraventricular hemorrhage during the study period. Four-channel 24-h cassette recordings were obtained on day 1, 3-5 and 7-9. For each of the 24-h recordings, the percentage of the time showing stage I (continuous activity), stage II (mixed activity) and stage III (discontinuous activity) epochs was calculated. In infants without periventricular-intraventricular hemorrhage, a positive linear relationship between gestational age and continuous activity and a negative linear relationship between gestational age and discontinuous activity existed in the first day recordings; in infants with periventricular-intraventricular hemorrhage, such relationships were not found. To determine if the changes in continuous and discontinuous activities during the first week of extrauterine life were different from the expected changes during a corresponding time in utero, we calculated the expected amounts of stage I and III changes for each infant. The actual changes were not significantly different from the expected values in both study groups. However, during the onset and/or extension of periventricular-intraventricular hemorrhage, depression of the electroencephalographic background activity was found.

Scaling and organization of electroencephalographic background activity and alpha rhythm in healthy young adults

The coexistence of the broad-band fluctuation and alpha rhythm of the brain dynamics is studied based on the zero-crossing property of the local electroencephalographic (EEG) recording in eyes closed and eyes open. A two-component zero-crossing scenario, consisting of a broad-band fractal and narrow-band rhythm components, is assumed. Scaling is found in the power law distribution p(tau) approximately tau(-nu) of the crossing time interval tau of the broad-band fluctuation. In alpha dominant brain state, the alpha rhythm interval L also exhibits scaling in the form of power law distribution: p(L) approximately L(phi). Our main result is the relationship nu + phi approximately 3 that characterizes the organization of these two prominent features of the brain dynamics. The possible role of self-organized criticality of punctuated equilibrium in this organization is discussed.

Prediction of Seizures in Asphyxiated Neonates: Correlation With Continuous Video-Electroencephalographic Monitoring

After perinatal asphyxia, predicting which infants will develop significant hypoxic-ischemic encephalopathy and neonatal seizures remains a difficult task. High-risk markers (Apgar score, acidosis, nucleated red blood cells, and resuscitation) have been used to predict neonatal seizures with varying success. The "3 strikes" of Apgar score of <5 at 5 minutes, pH <7.00, and need for intubation have been cited as having a positive predictive value of 80%. We examined whether the predictive values of these markers would be increased if early continuous electroencephalographic monitoring allowed us to accurately identify all neonatal seizures and to grade the encephalopathy. We recruited term infants with perinatal asphyxia. Continuous video electroencephalography was commenced soon after birth and continued for 24 to 72 hours. The abilities of high-risk markers to predict electroencephalographic seizures, background electroencephalographic activity, and Sarnat grade were examined. Forty-nine infants were suitable for analysis. Electrographic seizures occurred in 11 of the 49 infants. Encephalopathy was scored by using Sarnat grade (6, severe; 18, moderate; 25, mild) and electroencephalographic findings (4 inactive, 4 major abnormalities, 16 moderate abnormalities, and 25 normal/mildly abnormal). Apgar score of <5 at 5 minutes, pH <7.0, and the need for intubation had positive predictive values for neonatal seizures of 18%, 16%, and 21%, respectively. Combining these markers gave a positive predictive value of 25% and a negative predictive value of 77%. Substituting base deficit or lactate for pH in the 3-strikes model did not improve its predictive value. Apgar score of <5 at 5 minutes, nucleated red blood cells, and a base deficit less than -15 mEq/L showed some association with Sarnat grade. Only 5-minute Apgar score was significantly associated with both Sarnat grade and electroencephalographic grade. After perinatal asphyxia, neither the condition at birth nor the degree of metabolic acidosis reliably predict neonatal seizures.

Effect of Genetically Caused Excess of Brain Gamma-Hydroxybutyric Acid and GABA on Sleep

Exogenous gamma-hydroxybutyrate (GHB) increases slow-wave sleep and reduces daytime sleepiness and cataplexy in patients with primary narcolepsy. To examine nighttime sleep and daytime sleepiness in a 13-year-old girl homozygous for succinic semialdehyde dehydrogenase (SSADH) deficiency, a rare recessive metabolic disorder that disrupts the normal degradation of 4-aminobutyric acid (GABA), and leads to an accumulation of GHB and GABA within the brain. Sleep interview, nighttime polysomnography, Multiple Sleep Latency Tests, and continuous 24-hour in-lab recordings in the patient; overnight polysomnography in her recessive mother and in a 13-year-old female control. During quiet wakefulness, background electroencephalographic activity was slow and composed of 7-Hz activity. Sleep stage 3/4 was slightly increased (28.1% of total sleep period, norms 15%-28%), and the daytime mean sleep latency was short in the patient (3 minutes 42 seconds, norms > 8 minutes). Stage 2 spindles were infrequent in the child (0.18/minute, norms: 1.2-9.2/minute) and her mother (0.65/minute) but normal (4.6/minute) in the control. At the beginning of the second night, a tonic-clonic seizure occurred, followed by a dramatic increase in stage 3/4 sleep, that lasted 46.3 % of the total sleep period, double the normal value. The mother showed a reduced total sleep time and rapid eye movement sleep percentage. This suggests that a chronic excess of GABA and GHB induces subtle sleep abnormalities, whereas increased slow-wave sleep evoked by a sudden event (here an epileptic seizure) may be caused by a supplementary increase in GABA and GHB.

MASTER: a Windows program for recording multiple auditory steady-state responses

MASTER is a Windows-based data acquisition system designed to assess human hearing by recording auditory steady-state responses. The system simultaneously generates multiple amplitude-modulated and/or frequency-modulated auditory stimuli, acquires electrophysiological responses to these stimuli, displays these responses in the frequency-domain, and determines whether or not the responses are significantly larger than background electroencephalographic activity. The operator can print out the results, store the data on disk for more extensive analysis by other programs, review stored data, and combine results. The system design follows clear principles concerning the generation of acoustic signals, the acquisition of artifact-free data, the analysis of electrophysiological responses in the frequency-domain, and the objective detection of signals in noise. The instrument uses a popular programming language (LabVIEW) and a commercial data acquisition board (AT-MIO-16E-10), both of which are available from National Instruments.

Effects of remacemide and its metabolite FPL 12495 on spike-wave discharges, electroencephalogram and behaviour in rats with absence epilepsy

The effects of the anti-convulsant drug remacemide and one of its active metabolites FPL 12495 were examined in a genetic model for generalized absence epilepsy, the WAG/Rij strain of rats. Number, mean and total duration of spike-wave discharges were measured following oral administration of remacemide and FPL 12495, together with parameters of background electroencephalographic activity (EEG) and spontaneous behaviour in the recording cage. A decrease in the number of the spike-wave discharges was found after remacemide administration. At the highest dose there was near total suppression of the spike-wave discharges. There were no important effects on behaviour and on spectral content of the background EEG, suggesting that remacemide has little side effects. A decrease in the number of spike-wave discharges was also found after FPL 12495 gavage and there was a prolongation of the mean duration. Behavioural changes were only noticed after the highest dose. These were accompanied by changes in the spectral content and particularly by an increase in the amplitude of the delta and the high beta frequencies, together with a decrease in the spindle frequency range. FPL 12495 appeared to be more potent that remacemide in all its effects. The effects of mainly FPL 12495 are uncommon in the sense that so far no other investigated drug shows a decrease in the number together with an increase in the mean duration of the discharges. It seems that in contrast to other anti-epileptic drugs, FPL 12495 exerts a differential action on the two commonly distinguished mechanisms controlling number and duration.

Nucleus basalis lesions suppress spike and wave discharges in rats with spontaneous absence-epilepsy

Cholinergic drugs were shown to affect spike and wave discharges in a selected strain of Wistar rats with generalized non-convulsive absence epilepsy, named GAERS (Genetic Absence Epilepsy Rats from Strasbourg). The involvement of cholinergic transmission from the nucleus basalis in the control of absence seizures in GAERS was investigated in the present study, by examining the effects of unilateral excitotoxic lesions of this nucleus on the occurrence of spike-wave discharges. Ibotenate (0.01 M) and quisqualate (0.03 and 0.06 M)-induced lesions of the nucleus basalis suppressed spike-wave discharges in the cortex ipsilateral to the lesion. The suppression was associated with a disappearance of both acetylcholinesterase-fibres in the cerebral cortex and choline acetyltransferase immunopositive neurons within the nucleus basalis. Concomitantly, the background electroencephalographic activity was slowed. These results suggest that cholinergic innervation of the cerebral cortex by the nucleus basalis is involved in the occurrence of generalized non-convulsive seizures, in relation to the control of cortical activation.

Artifact detection and removal during auditory evoked potential monitoring.

Various artifacts can distort or obscure evoked potential waveforms. The algorithms presented in this paper scan the output electroencephalographic signal for artifacts during evoked potential recordings. If possible, the artifact is removed; if not possible, that sweep is excluded from the averaging process required to raise the evoked response above the background electroencephalographic activity. An artifact is detected if 1 or more amplitude or frequency parameters exceed a threshold. These thresholds have been determined after constructing histograms of the parameters concerned using a number of control evoked potential recordings containing no visually recognizable artifacts. The distributions of the parameters shown by these histograms give information about their normal range. The method improves the quality of the waveform in many cases, but its effectiveness strongly depends on the characteristics of the artifacts concerned.

No confirmation of visual evoked potential diagnostic test for migraine

We have attempted to replicate the results of studies on a diagnostic test reported to have 90% sensitivity and 89-96% specificity for migraine. The technique is based on peak-to-peak measurements of fast background electroencephalographic activity during a visual evoked potential (VEP) study. VEP latencies and amplitudes did not differ significantly, and showed substantial overlap, between a group of eight migraine patients and ten age-matched healthy controls. We could not recognise previously described fast activity or measure it objectively by peak-to-peak measurements. We cannot confirm that measurement of fast wave activity in the VEP background is useful in diagnosis of migraine.

Neonatal herpes simplex virus infection

We present a series of 43 infants with neonatal herpes simplex virus infection treated at the Children's Hospital, University of Helsinki, during a 16-year period from 1970 to 1985. Twelve mothers (28%) had a history of genital herpes during pregnancy, and two had had labial herpes infection. Eight infants (19%) were delivered by cesarean section. In 14 (33%) infants symptoms appeared within 24 hours and in 26 (61%) they appeared within 7 days. The presenting symptoms were neurologic in 79%, cutaneous in 30%, respiratory in 19%, cyanosis/pallor/grayish skin in 16%, irritability in 12% and fever in 7%. Herpes simplex virus was detected most early and frequently in pharyngeal swabs, in one-third on Postnatal Days 2 to 5. Cerebrospinal fluid contained an increased amount of protein and/or pleocytosis in 72%. Abnormal electroencephalographic background activity appeared in 56% and electrical paroxysms in 41%. Six infants (14%) died, 9 (21%) were damaged severely and 6 (14%) were moderately or mildly damaged. Poor prognosis was associated with acute maternal illness at delivery, prematurity, visceral involvement and/or electrical paroxysms in the electroencephalograms. This study underlines the occurrence of intrauterine transmission of herpes virus, infections with neurologic manifestations, early symptomatology and the need for prompt diagnosis, brain biopsy in selected patients and antiviral therapy in neonates with herpes virus infection.

Extraction of clinical information from electroencephalographic background activity: the combined use of brain electrical activity mapping and intravenous sodium thiopental.

Traditional visual inspection of electroencephalographic (EEG) tracings and computer-assisted topographic mapping were compared in their abilities to detect and locate supratentorial lesions following intravenous sodium thiopental administration. Of the 13 subjects, 8 had atrophic and 5 had mass lesions, all defined by computed tomographic scan and 11 confirmed at operation. EEGs made before and after thiopental administration were evaluated separately from topographic maps of statistical difference between EEGs at multiple frequency ranges made before and after thiopental injection. Topographic mapping of statistical difference accurately detected all thirteen lesions, whereas EEG detected eight. In addition to demonstrating reduced beta production overlying structural abnormalities, topographic mapping revealed regionally augmented beta, especially over irritative lesions. Moreover, localization was possible with the topographic method after the first thiopental injection, whereas a second injection was required for EEG localization by visual inspection. Changes in slow (delta) activity were also useful in delineation of atrophic lesions, in which delta was usually augmented but occasionally regionally reduced. Multielectrode studies with topographic mapping appear essential in delineating cerebral abnormalities, because both slow and fast activities may be increased or reduced over such areas. The relative response of EEG background activity to thiopental at different frequencies may assist lesion characterization as well as localization.