EEG Montage Research Articles

Classifier models and architectures for EEG-based neonatal seizure detection

Neonatal seizures are the most common neurological emergency in the neonatal period and are associated with a poor long-term outcome. Early detection and treatment may improve prognosis. This paper aims to develop an optimal set of parameters and a comprehensive scheme for patient-independent multi-channel EEG-based neonatal seizure detection. We employed a dataset containing 411 neonatal seizures. The dataset consists of multi-channel EEG recordings with a mean duration of 14.8 h from 17 neonatal patients. Early-integration and late-integration classifier architectures were considered for the combination of information across EEG channels. Three classifier models based on linear discriminants, quadratic discriminants and regularized discriminants were employed. Furthermore, the effect of electrode montage was considered. The best performing seizure detection system was found to be an early integration configuration employing a regularized discriminant classifier model. A referential EEG montage was found to outperform the more standard bipolar electrode montage for automated neonatal seizure detection. A cross-fold validation estimate of the classifier performance for the best performing system yielded 81.03% of seizures correctly detected with a false detection rate of 3.82%. With post-processing, the false detection rate was reduced to 1.30% with 59.49% of seizures correctly detected. These results represent a comprehensive illustration that robust reliable patient-independent neonatal seizure detection is possible using multi-channel EEG.

REM sleep EEG spectral analysis in patients with first-episode schizophrenia

The pathophysiology of schizophrenia includes abnormalities in subcortical–cortical transfer of information that can be studied using REM sleep EEG spectral analysis, a measure that reflects spontaneous and endogenous thalamocortical activity. We recorded 10 patients with first-episode schizophrenia and 30 healthy controls for two consecutive nights in a sleep laboratory, using a 10-electrode EEG montage. Sixty seconds of REM sleep EEG without artifact were analyzed using FFT spectral analysis. Absolute and relative spectral amplitudes of five frequency bands (delta, theta, alpha, beta1 and beta2) were extracted and compared between the two groups. Frequency bands with significant differences were correlated with BPRS positive and negative symptoms scores. Patients with schizophrenia showed lower relative alpha and higher relative beta2 spectral amplitudes compared to healthy controls over the averaged total scalp. Analysis using cortical regions showed lower relative alpha over frontal, central and temporal regions and higher relative beta2 over the occipital region. Absolute spectral amplitude was not different between groups for any given EEG band. However, absolute alpha activity correlated negatively with BPRS positive symptoms scores and correlated positively with negative symptoms scores. Since similar results have been reported following EEG spectral analysis during the waking state, we conclude that abnormalities of subcortical–cortical transfer of information in schizophrenia could be generated by mechanisms common to REM sleep and waking.

Characterization of neonatal seizures by conventional EEG and single-channel EEG

Objective To perform a detailed, contemporary temporal–spatial characterization of neonatal seizures (NS) and to compare conventional EEG (CEEG) to single-channel EEG for NS detection. Methods Digitally recorded CEEGs were reviewed for NS characteristics (quantity, duration, location of onset, peak-to-peak amplitude). The presence and characteristics of each NS were simultaneously noted in a single, derived EEG channel (C 3 → C 4). Results Eight hundred fifty-one seizures from 125 CEEGs recorded were analyzed. Mean seizure rate was 7.0 NS/h (range: 0.5–21). Mean seizure burden (percent time CEEG showed NS at any location) was 24.8% (range: 0.7–86.9). Seizure rate was only moderately correlated with seizure burden (Spearman coefficient = 0.58). Eighty-one percent of NS originated from central–temporal or midline vertex electrodes. Seventy-eight percent of NS appeared in the C 3 → C 4 channel. Conclusions Accurate measurement of NS burden requires detailed temporal–spatial characterization. The theoretical ceiling of sensitivity for NS detection in the single EEG channel C 3 → C 4 is high. However, further processing the raw EEG in limited electrode arrays may reduce the sensitivity of NS detection. Significance CEEG is the gold standard for NS detection. However, reduced montage EEG techniques are increasingly available. This detailed contemporary temporal–spatial characterization of NS evaluates the potential limitations of reduced montage techniques.

Exploratory Polysomnographic Evaluation of Pregabalin on Sleep Disturbance in Patients with Epilepsy

To evaluate the effects of adjunctive pregabalin 300 mg/day versus placebo on polysomnographic (PSG) variables in patients with well controlled partial seizures and subjectively reported sleep disturbance. An exploratory, 4-week, double-blind, randomized study in patients with well controlled partial seizures on AED monotherapy and subjective sleep disturbance over the previous 6 months. Mean changes from baseline to endpoint in PSG and subjective sleep variables (MOS Sleep Scale, Groningen Sleep Questionnaire) in patients on adjunctive pregabalin 300 mg/day (n=8) were compared with patients on placebo (n=7). Baseline PSGs showed sleep fragmentation. Mean sleep efficiency improved significantly in both treatment groups in the mean baseline to endpoint change; there was no significant between-group difference. Pregabalin treatment was associated with a significant reduction in number of awakenings (p = 0.02), and improvement in wake time after sleep onset approached significance (p = 0.055), suggesting improvement in sleep continuity that was not observed in the placebo group. Pregabalin was also associated with significant improvements in the MOS sleep disturbance and sleep quantity subscales compared with placebo (p < or =0.03). There were no changes in self-reported seizure control. This exploratory pilot study suggests that pregabalin may improve sleep continuity in patients with clinically relevant sleep disturbance. The effect on disturbed sleep appears independent of seizure control. The effects of pregabalin on disturbed sleep and seizures and their interrelationships warrant further study.

Prevalence of epileptiform activity in healthy children during sleep

Background The term epileptiform discharge typically refers to interictal paroxysmal activity that occurs more commonly during sleep. This type of paroxysmal activity does not include the electroencephalographic (EEG) activity observed during a seizure. The prevalence of epileptiform activity in the general pediatric population is unknown. Methods Polysomnographic (PSG) studies were conducted in otherwise healthy children recruited from the general population and with no previous history of seizures or any other medical conditions. All sleep studies included an eight-lead EEG montage. Spike and sharp waves, either alone or accompanied by slow waves, occurring singly or in bursts lasting <5 s were considered as representing epileptiform activity. Results Nine hundred seventy children underwent overnight PSG. In 14 children, evidence of epileptiform activity, in the absence of any additional abnormality in the PSG, occurred. Thus, the prevalence of epileptiform activity was 1.45%. Epileptiform patterns found were either spike or spike and wave and were more prominent during non-rapid eye movement (NREM) sleep, with 11 patients presenting spike and spike and wave patterns in the centro-temporal regions. Four of the six children who underwent neurocognitive tests exhibited abnormal findings in areas of behavior, attention, hyperactivity, and learning. Conclusion Epileptiform activity in otherwise healthy children from the community is relatively frequent and, if confirmed by prospective studies, could be associated with suboptimal cognitive and behavioral functions. Increased awareness by sleep professionals and use of PSG montage that includes temporal leads and >2 standard EEG leads should facilitate the detection of epileptiform activity in children.

The Characteristics Of Recovery Sleep When Recovery Opportunity Is Restricted

The aim of this study was to investigate the recovery of sleep and waking functions following one night of total sleep deprivation, when recovery opportunity was either augmented or restricted. The 9-day laboratory study involved a baseline night, a night of sleep loss (approximately 40 h) followed by 5 nighttime recovery sleep periods. Recovery consisted of either five 9-h sleep opportunities or five 6-h sleep opportunities. All data collection took place in a controlled laboratory environment at the Centre for Sleep Research. A total of n = 20 healthy adults (18-35 yrs) participated in the study. Each sleep period was recorded using a standard polysomnographic EEG montage. Waking functions were assessed every 2 hours during all wake periods, using a 10 minute psychomotor vigilance task (PVT) and a subjective alertness visual analogue scale (VAS). Sleep analyses indicated that across the week TST, SOL, REM, and sleep efficiency varied significantly between the 2 conditions, but amounts of SWS did not. Waking functions in the 9-h condition recovered after one sleep period. In the 6-h condition however, mean response time on the PVT was 10% below baseline and subjective alertness 20% below baseline for the entire recovery period. The results suggest that TST is a key factor in determining recovery. When recovery opportunity is restricted, both sleep variables and measures of waking functions do not recover.

ALTERED BRAIN WAVE ACTIVITY IN PERSONS WITH CHRONIC SPINAL CORD INJURY

This study investigated brain wave activity associated with spinal cord injury (SCI). Electroencephalograms (EEG) were compared between 10 individuals with SCI and 10 age and sex matched able-bodied controls using a 64-channel EEG montage. SCI participants had chronic (>12 months) paraplegic clinically complete injuries. The 64 channels of EEG data were spread diffusely over the cortex and were compared for delta (2–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), and beta (13–30 Hz) wave components of the EEG frequency spectra. No significant magnitude or directional changes were found in the delta (2–4 Hz) or theta (4–8 Hz) wave frequency bands between these two groups. However, significant and consistent decreased alpha wave (8–13 Hz) and increased beta wave activity (13–30 Hz) were found in the SCI participants across the cortex compared to the able-bodied control group. These findings suggest that the SCI group have increased neural processing compared to the able-bodied individuals, which may be related to ongoing reorganization of brain structures following SCI.

P432 Using a questionnaire to identify patients at risk for the sleep apnea syndrome

from the Somte montage but these were not clinically important. The Somte significantly underestimated the number of arousals but the number of respiratory events was the same. The positive predictive value for the Somte to detect RDI > 15 was 100% and for RDI > 30 was 80%. Conclusions: In an unselected sleep laboratory population, in the hands of experienced scorers, the Somte accurately measured sleep and respiratory parameters despite the limited EEG montage. Arousals were harder to detect and were underestimated on the Somte . In a laboratory setting the accuracy of the Somte modified polysomnography device was considered adequate for clinical purposes.

Interictal, Potentially Misleading, Epileptiform EEG Abnormalities in REM Sleep Behavior Disorder

To examine the implications of interictal epileptiform abnormalities (IEA) in idiopathic REM-sleep behavior disorder (RBD), particularly the risk of misdiagnosing RBD episodes as epileptic nocturnal seizures. Observational analysis and review. Tertiary sleep center. Thirty patients (28 men; mean age 66.3 +/- 7.5 years) referred to our sleep unit for a definite diagnosis of nocturnal sleep-related motor and behavioral paroxysmal episodes. N/A. All the patients were found to be affected by idiopathic RBD according to standard clinical and videopolysomnographic criteria. IEA(sporadic, fronto-temporal sharp-waves) were detected in 8 subjects (26.6%) during routine electroencephalogram and/or nocturnal in-lab videopolysomnography with extended EEG montages. In 2 of these 8 patients, IEA occurred during REM sleep. When only the clinical history is considered, RBD episodes may be confused with nocturnal epileptic focal seizures. The presence of IEA either on routine awake electroencephalograms, or during sleep electroencephalograms, may add support for a diagnosis of epileptic nocturnal seizures. Our data show that IEA may occur in wake and sleep (non rapid eye movement and rapid eye movement sleep) tracings of subjects with episodes of idiopathic RBD. However full-night extended electroencephalogram montages and polysomnography recording of an episode proved useful in establishing a definite diagnosis of RBD in these potentially misleading cases. Comparison of the patients' demographic data and RBD features revealed no differences between RBD with IEA and without IEA. On this basis-and given that these abnormalities have also been described in elderly people with wakefulness-related nonepileptic disorders-IEA in RBD could simply be interpreted as a nonspecific phenomenon, probably related to brain aging.

Accuracy of Seizure Detection Using Abbreviated EEG During Polysomnography

The purpose of this study was to determine the validity of abbreviated EEG montages for seizure detection during polysomnography. Three electroencephalographers reviewed files containing seizures or nonepileptic events using 8- and 18-channel montages. Files were rated as to whether they contained seizures and assigned a "probability of seizure" score from 0% to 100% reflecting the confidence that it was a seizure. Readers then localized seizures as temporal, frontal, parieto-occipital, or nonlocalized and provided a probability of correct localization with 0% to 100% confidence. Data were analyzed using the Adjusted McNemar Test method of Obochuwski. The probability of seizure score was measured using the receiver operating characteristic curve. Observed agreement was 78% and 84% for 8- and 18-channel montages, respectively. Readers were better able to distinguish seizures from nonepileptic events using the 18-channel montage (P = 0.004). Seizures localized to the temporal and parieto-occipital regions were more likely to be correctly identified and localized. Readers were able to correctly localize 27% and 49% of seizures using the 8- and 18-channel montages, respectively (P < 0.001). Abbreviated EEG montages are inadequate in the differentiation of seizures and nonepileptic events arising from sleep during polysomnography. This seems to be particularly true in frontal lobe epilepsy.

Train Drivers' Sleep Quality and Quantity during Extended Relay Operations

Relay operations are an important mode of freight transportation within Australia. Relay work requires multiple crews to drive the train continuously from one specified destination to another and return. Importantly, the nature of relay work requires train drivers to sleep on‐board during designated resting shifts. The main aim of the present study was to investigate the quality and quantity of sleep obtained in on‐board rest facilities (relay vans) during extended (four‐day) relay operations. Drivers (n=9) working the Port Augusta to Darwin relay operation volunteered to participate. The first leg of the trip typically took 40 h followed by an overnight stay in Darwin (between 8–12 h) prior to return. Two crews, each consisting of two drivers, changed every 8 h, giving the crew an 8 h rest in the relay van prior to each 8 h working shift. Using polysomnography, home sleep data were collected prior to and following each trip using a standard five‐channel EEG montage. All sleep periods during the relay trip (including Darwin) were also recorded. Additionally, subjective sleep quality ratings were recorded following each sleep period. Analyses revealed that the quantity of sleep obtained in the relay vans (3.3 h) was significantly reduced compared to home (6.8 h). In general, the total sleep time was increased at night and reduced during the day. In terms of quality, sleep onset latency, sleep efficiency, and amount of slow wave and rapid eye movement sleep did not differ significantly between home and the relay vans. The results of the study highlight sleep quantity as the main concern during extended relay operations. Future research should focus on investigating the subjective and objective impact of this sleep reduction on waking functions.

Principal components analysis of Laplacian waveforms as a generic method for identifying ERP generator patterns: II. Adequacy of low-density estimates

Objective To evaluate the comparability of high- and low-density surface Laplacian estimates for determining ERP generator patterns of group data derived from a typical ERP sample size and paradigm. Methods High-density ERP data (129 sites) recorded from 17 adults during tonal and phonetic oddball tasks were converted to a 10–20-system EEG montage (31 sites) using spherical spline interpolations. Current source density (CSD) waveforms were computed from the high- and low-density, but otherwise identical, ERPs, and correlated at corresponding locations. CSD data were submitted to separate covariance-based, unrestricted temporal PCAs (Varimax of covariance loadings) to identify and effectively summarize temporally and spatially overlapping CSD components. Solutions were compared by correlating factor loadings and scores, and by plotting ANOVA F statistics derived from corresponding high- and low-resolution factor scores using representative sites. Results High- and low-density CSD waveforms, PCA solutions, and F statistics were remarkably similar, yielding correlations of .9≤ r≤.999 between waveforms, loadings, and scores for almost all comparisons at low-density locations except for low-signal CSD waveforms at occipital sites. Each of the first 10 high-density factors corresponded precisely to one factor of the first 10 low-density factors, with each 10-factor set accounting for the meaningful CSD variance (>91.6%). Conclusions Low-density surface Laplacian estimates were shown to be accurate approximations of high-density CSDs at these locations, which adequately and quite sufficiently summarized group data. Moreover, reasonable approximations of many high-density scalp locations were obtained for group data from interpolations of low-density data. If group findings are the primary objective, as typical for cognitive ERP research, low-resolution CSD topographies may be as efficient, given the effective spatial smoothing when averaging across subjects and/or conditions. Significance Conservative recommendations for restricting surface Laplacians to high-density recordings may not be appropriate for all ERP research applications, and should be re-evaluated considering objective, costs and benefits.

Topographic abnormality of slow cortical potentials in schizophrenia.

A recent study from our laboratory has provided evidence for the generation of slow potentials occurring in anticipation to task-performance feedback stimuli, in multiple association cortical areas, consistently including two prefrontal areas. In the present study, we intended to determine whether these slow potentials would indicate some abnormality (topographic) in schizophrenic patients, and thus serve as an indication of abnormal association cortex activity. We recorded slow potentials while subjects performed a paired-associates memory task. A 123-channel EEG montage and common average reference were used for 20 unmedicated schizophrenic (mean duration of illness: 11.3 +/- 9.2 years; mean number of previous hospitalizations: 1.2 +/- 1.9) and 22 healthy control subjects during a visual paired-associates matching task. For the topographic analysis, we used a simple index of individual topographic deviation from normality, corrected for absolute potential intensities. Slow potentials were observed in all subjects. Control subjects showed a simple spatial pattern of voltage extrema (left central positive and right prefrontal negative), whereas schizophrenic patients presented a more complex, fragmented pattern. Topographic deviation was significantly different between groups (P<0.001). The increased topographic complexity in schizophrenics could be visualized in grand averages computed across subjects. Increased topographic complexity could also be seen when grand averages were computed for subgroups of patients assembled either according to task-performance (high versus low) or by their scores on psychopathological scales. There was no significant correlation between topographic deviation and psychopathology scores. We conclude that the slow potential topographic abnormalities of schizophrenia indicate an abnormality in the configuration of large-scale electrical activity in association cortices.

Hyperkinetic seizures in children.

The objective of this study was to delineate the clinical and video-electroencephalographic (EEG) manifestations of children with complex partial seizures with a predominant "hyperkinetic" presentation. Certain types of partial seizures can be difficult to differentiate from nonepileptic seizures because of their intense motor presentation and, at times, lack of alteration of consciousness. Based on a published semiologic seizure classification, this type of seizures can be described as "hyperkinetic," characterized by intense motor activity involving the extremities and trunk. We report five children diagnosed with hyperkinetic seizures by video-EEG monitoring. All patients were referred for video-EEG evaluation because of an initial suspicion of pseudoseizures. Presented in this study is a review of the patients' clinical data, including video-EEG evaluation. There were three boys and two girls; the mean age at presentation was 10 +/- 3 years. In four patients, there was a history of behavioral disorder, with two patients carrying a diagnosis of attention-deficit hyperactivity disorder (ADHD). One girl had significant developmental delay and an abnormal neurologic examination. Brain magnetic resonance imaging was normal in three patients and abnormal in two. The semiology of the seizures consisted of stereotypic intense motor activity, mainly upper extremity flailing and kicking. Screaming and shouting were noted in three cases, and intense fear was present in two patients. The hyperkinetic ictal activity progressed to tonic-clonic seizures in two patients. Seizures occurred out of sleep or on awakening in four patients. The interictal EEG activity was normal in one patient and revealed a continuous generalized slowing and slowing of the posterior dominant rhythm in two patients. One of the latter patients had interictal epileptiform activity in the frontal and midline regions. An intermittent rhythmic slow activity of the left hemisphere with superimposed bifrontal sharp waves was noted in the fifth patient. The ictal EEG revealed profuse superimposed electromyographic (EMG) activity in all patients, making some of the EEG interpretation difficult to analyze, particularly a longitudinal bipolar montage. However, with digital manipulation of the ictal EEG data, such as changes in EEG sensitivity, application of fast frequency filters, and use of different EEG montages, it was possible to discern an ictal EEG pattern or postictal slowing following the diffuse EMG artifact in all patients. On clinical follow-up, adequate seizure control was achieved in three patients. Based on the clinical history, one patient was diagnosed with autosomal dominant nocturnal frontal lobe epilepsy. Diagnosis of hyperkinetic seizures can be difficult because of the similarity of the clinical manifestations with nonepileptic events such as certain parasomnias and pseudoseizures. Video-EEG is the most effective way of diagnosing this type of seizure.

Modulation of induced gamma band responses in a perceptual learning task in the human EEG.

Fragmented pictures of an object, which appear meaningless when seen for the first time, can easily be identified after the presentation of an unfragmented version of the same picture. The neuronal mechanism for such a rapid perceptual learning phenomenon is largely unknown. Recently, induced gamma band responses (GBRs) have been discussed as a possible physiological correlate of activity in cell assemblies formed by learning. The present study was designed to investigate the modulation of induced GBRs in a perceptual learning task by using a 128-channel EEG montage. In the first sequence of the experiment, fragmented pictures from the Snodgrass and Vandervart inventory were presented. The fragmentation of the pictures was selected that subjects were unable to identify them. In the second experimental sequence - the perceptual learning sequence - half of the pictures were displayed in their unfragmented version. In the third sequence, all pictures were presented again in the fragmented version. Now, subjects had to rate whether or not they could identify the images. Results showed an increase in spectral gamma power at parietal electrode sites for identified pictures. In addition, neural activity in the gamma band was highly synchronized between posterior electrodes. For pictures not presented in their complete version, we found no such pattern in the third sequence. From our results, we concluded that induced GBRs might represent a signature of synchronized neural activity in a Hebbian cell assembly, activated by the fragmented picture after perceptual learning took place. No difference between identified and unidentified pictures was found in the visual evoked potential in the same time range and in the evoked GBR in the same frequency range as the induced response.

Effects of modeling errors and EEG measurement montage on source localization accuracy.

The location of an electrical source in the brain can be determined from the EEGs the source produces on the scalp by calculating the location of a source in a model of the head using the EEGs. Modeling errors produced by differences between the actual head and the head model cause localization errors (i.e., errors in the calculated location of the source). This is a study of the localization errors caused by modeling errors produced by the differences between two features of actual head geometry and a spherical head model. The two features are general nonspherical head shape and the brain pan (i.e., the very nonspherical lower surface of the brain cavity). This is also a study of the localization accuracy of different EEG measurement montages when these modeling errors are present. It has been found that general nonspherical head shape causes maximum localization errors of approximately 1 cm, and that these errors are not very dependent on source location or orientation, or EEG montage. The localization errors caused by the brain pan are generally larger: The maximum error is approximately 2 cm. These errors are very dependent on source location and orientation, and EEG montage. The largest errors occur for sources close to and pointing toward the brain pan surface. These errors also vary widely with montage: A referential montage with the reference point on the bottom of the model has the largest errors. Referential montages with reference points on the side or top of the model, an average reference montage, or a bipolar montage generally produce much smaller errors.

Identifying Montages that Best Detect Electrographic Seizure Activity During Polysomnography

Recognizing epileptic seizures during video polysomnography (VPSG) can be challenging, particularly when using standard, limited EEG montages and paper speed. Few sleep laboratories have PSG equipment that allows for the recording of 18 channels of EEG without compromising the ability to detect sleep apnea, periodic limb movements, and parasomnias. We studied the ability of sleep medicine- and EEG-trained polysomnographers to correctly identify epileptic seizures during PSG using 4, 7, and 18 channels of simultaneous EEG, recording at conventional PSG and EEG paper speeds. The purpose of this study was to determine the value of limited EEG montages viewed with EEG reformatting capability in the identification of seizures during PSG. Blinded EEG analysis of seizures and arousals during VPSG. Tertiary care hospital with sleep laboratory and epilepsy monitoring unit. Subjects with focal (partial) epilepsy that underwent video-EEG monitoring. We designed two 7-channel EEG montages that might facilitate the identification of seizures arising from the frontal and temporal lobes. Sleep medicine- and EEG-trained polysomnographers were asked to review tracings containing frontal or temporal lobe epileptic seizures and arousals from sleep. Utilizing the capability of our digital recording equipment to reformat EEG channels and change paper speeds, we asked the readers to classify events recorded with 4, 7, and 18 channels of simultaneous EEG, at paper speeds of 10 and 30 mm/sec. 6 readers viewed 32 sleep-related events (13 frontal lobe seizures, 11 temporal lobe seizures, and 8 arousals). The following factors were analyzed for their influence on accuracy of event detection: 1) the type of training of the reader (EEG vs. sleep medicine); 2) the number of EEG channels (4, 7, or 18); and 3) paper speed (10 vs. 30 mm/sec). Pair-wise comparisons and generalized estimating equations were used to identify factors leading to more accurate detection of seizures and arousals. 77% of events were correctly identified: 74% of seizures and 88% of arousals. Seizure detection was better using 7 and 18 channels (sensitivity of 82% and 86%, respectively) than 4 EEG channels (sensitivity of 67%) for temporal lobe seizures only. The number of EEG channels did not affect the accuracy of frontal lobe seizure detection. For EEG-trained readers, accuracy was greater using 30 mm/sec than 10 mm/sec paper speed (85% vs. 78% correct, respectively). Adding EEG channels and EEG reformatting capabilities to PSG interpretation improves the detection of some types of epileptic seizures. Accuracy of temporal lobe seizure detection using an abbreviated 7-channel montage approximates that of an 18-channel EEG recording. However, the same is not true of frontal lobe seizures in which accuracy was similar regardless of the number of EEG channel available. Further studies are needed to identify specific EEG montages that would best detect epileptiform activity during VPSG.

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 H 2 15O 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.

A laboratory study of sleep and dreaming in a case of Asperger's Syndrome.

Asperger's Syndrome (AS) is a pervasive developmental disorder whose continuity with High-Functioning Autism is still a matter of debate. Clinical observations suggest that patients with AS may present the same sleep disorders as autistic patients, including difficulties in initiating and maintaining sleep as well as poor dream recall. We recorded the sleep of a 25-year-old male patient with AS for two nights using a full EEG montage and compared the second night to that of a group of normal participants. We found low levels of slow wave sleep (SWS: stages 3 + 4), high levels of stage 1, and a large number of awakenings. The organization of REM sleep was unremarkable, including normal REM density. Analyses of phasic EEG events revealed a very low incidence of sleep spindles and a normal number of K-complexes over bilateral frontal and central EEG leads. In order to collect dream reports, the patient was awakened three times over two nights following at least 15 minutes of REM sleep in each case. On each occasion the patient was not aware of any mental activity happening just prior to awakening. These observations are discussed with regards to the connections that may exist between EEG sleep spindle activity, selective attention, and the capacity to generate a dream report.

Improving source reconstructions by combining bioelectric and biomagnetic data

Objectives: A framework for combining bioelectric and biomagnetic data is presented. The data are transformed to signal-to-noise ratios and reconstruction algorithms utilizing a new regularization approach are introduced. Methods: Extensive simulations are carried out for 19 different EEG and MEG montages with radial and tangential test dipoles at different eccentricities and noise levels. The methods are verified by real SEP/SEF measurements. A common realistic volume conductor is used and the less-well-known in-vivo conductivities are matched by calibration to the magnetic data. Single equivalent dipole fits as well as spatiotemporal source models are presented for single and combined modality evaluations and overlaid to anatomic MR images. Results: Normalized sensitivity and dipole resolution profiles of these acquisition systems are derived from these synthetic data. The methods are verified by simultaneously measured somasensory data. Conclusions: Superior spatial resolution of the combined data studies is revealed, which is due to the complementary nature of both modalities and the increased number of sensors. a better understanding of the underlying neironal processes can be acheived, since an improved differentiation between quasi-tangential and quasi-radial sources is possible.