Referential Montage Research Articles

AN ANALYSIS OF TWO COMMON REFERENCE POINTS FOR EEGS.

Clinical electroencephalographic (EEG) data varies significantly depending on a number of operational conditions (e.g., the type and placement of electrodes, the type of electrical grounding used). This investigation explores the statistical differences present in two different referential montages: Linked Ear (LE) and Averaged Reference (AR). Each of these accounts for approximately 45% of the data in the TUH EEG Corpus. In this study, we explore the impact this variability has on machine learning performance. We compare the statistical properties of features generated using these two montages, and explore the impact of performance on our standard Hidden Markov Model (HMM) based classification system. We show that a system trained on LE data significantly outperforms one trained only on AR data (77.2% vs. 61.4%). We also demonstrate that performance of a system trained on both data sets is somewhat compromised (71.4% vs. 77.2%). A statistical analysis of the data suggests that mean, variance and channel normalization should be considered. However, cepstral mean subtraction failed to produce an improvement in performance, suggesting that the impact of these statistical differences is subtler.

Evaluation of cortical local field potential diffusion in stereotactic electro-encephalography recordings: A glimpse on white matter signal

While there is a strong interest in meso-scale field potential recording using intracranial electroencephalography with penetrating depth electrodes (i.e. stereotactic EEG or S-EEG) in humans, the signal recorded in the white matter remains ignored. White matter is generally considered electrically neutral and often included in the reference montage. Moreover, re-referencing electrophysiological data is a critical preprocessing choice that could drastically impact signal content and consequently the results of any given analysis. In the present stereotactic electroencephalography study, we first illustrate empirically the consequences of commonly used references (subdermal, white matter, global average, local montage) on inter-electrode signal correlation. Since most of these reference montages incorporate white matter signal, we next consider the difference between signals recorded in cortical gray matter and white matter. Our results reveal that electrode contacts located in the white matter record a mixture of activity, with part arising from the volume conduction (zero time delay) of activity from nearby gray matter. Furthermore, our analysis shows that white matter signal may be correlated with distant gray matter signal. While residual passive electrical spread from nearby matter may account for this relationship, our results suggest the possibility that this long distance correlation arises from the white matter fiber tracts themselves (i.e. activity from distant gray matter traveling along axonal fibers with time lag larger than zero); yet definitive conclusions about the origin of the white matter signal would require further experimental substantiation. By characterizing the properties of signals recorded in white matter and in gray matter, this study illustrates the importance of including anatomical prior knowledge when analyzing S-EEG data.

Discrepancies between Multi-Electrode LFP and CSD Phase-Patterns: A Forward Modeling Study.

Multi-electrode recordings of local field potentials (LFPs) provide the opportunity to investigate the spatiotemporal organization of neural activity on the scale of several millimeters. In particular, the phases of oscillatory LFPs allow studying the coordination of neural oscillations in time and space and to tie it to cognitive processing. Given the computational roles of LFP phases, it is important to know how they relate to the phases of the underlying current source densities (CSDs) that generate them. Although CSDs and LFPs are distinct physical quantities, they are often (implicitly) identified when interpreting experimental observations. That this identification is problematic is clear from the fact that LFP phases change when switching to different electrode montages, while the underlying CSD phases remain unchanged. In this study we use a volume-conductor model to characterize discrepancies between LFP and CSD phase-patterns, to identify the contributing factors, and to assess the effect of different electrode montages. Although we focus on cortical LFPs recorded with two-dimensional (Utah) arrays, our findings are also relevant for other electrode configurations. We found that the main factors that determine the discrepancy between CSD and LFP phase-patterns are the frequency of the neural oscillations and the extent to which the laminar CSD profile is balanced. Furthermore, the presence of laminar phase-differences in cortical oscillations, as commonly observed in experiments, precludes identifying LFP phases with those of the CSD oscillations at a given cortical depth. This observation potentially complicates the interpretation of spike-LFP coherence and spike-triggered LFP averages. With respect to reference strategies, we found that the average-reference montage leads to larger discrepancies between LFP and CSD phases as compared with the referential montage, while the Laplacian montage reduces these discrepancies. We therefore advice to conduct analysis of two-dimensional LFP recordings using the Laplacian montage.

Fast (40–150 Hz) oscillations are associated with positive slow waves in the ictal EEGs of epileptic spasms in West syndrome

ObjectiveTo elucidate the generative mechanisms of epileptic spasms (ESs) in West syndrome, we investigated the temporal relationship between scalp fast (40–150Hz) oscillations (FOs) and slow waves in the ictal electroencephalograms (EEGs) of ESs. MethodsIn 11 infants with WS, ictal FOs were detected in a bipolar montage based on spectral and waveform criteria. Their temporal distribution was analyzed in terms of the positive peaks (trough point, TT) of identical EEG data in a referential montage. Among six EEG data sections defined according to TT, the number of FOs, peak power values, and peak frequencies were compared. ResultsWe identified a total of 1014 FOs (946 gamma and 68 ripple oscillations), which clustered closely at TT. The number of gamma oscillations in the 1s epoch including TT was significantly higher than those in the prior and subsequent phases. Peak power values and frequencies tended to be higher in these positive phase sections. ConclusionsThe temporal association of FO clustering and positive slow waves in the ictal EEGs of ES indicated that active neuronal firing related to FOs underlies the generation of ESs and their ictal slow waves.

6. Frontopolar sharp potentials

Sudden appearance of totally unexpected bisynchronous frontal-polar dominant unexpected potential initially embedded in eye blink with progressive recruitment and phase change. At times, it reaches up to 2.5 Hz, with awake background, and virtually minimal or limited spread to fronto-temporal or posterior frontal area on encephalogram. After very close examination and accepting wide variety of opinions, patient is being considered for epilepsy monitoring unit (EMU), so as same potential can be reproduced and evaluated for any fronto-polar epilepsies. Download : Download high-res image (572KB) Download : Download full-size image There are few unexpected potentials appears at fronto-polar region in EEG laboratory recording and must not escape, even though the patient has no additional oculographic leads. Potential described here, presented while ambulatory monitoring. The ocular potentials are mostly quite impressive and almost always give rise to marked eye movement artifacts in fronto-polar and anterior temporal leads. The use of polygraphic documentation makes the task much easier, as patient is being considered for EMU. When an REM phase occurs directly at sleep onset, the transition from drowsiness to REM is not very pronounced in the EEG, whereas the change from deep NREM sleep to REM is a very dramatic one ( Matsuo, 1981 ). During photic stimulation, light from the flash stimulus may produce artifact in the fronto-polar leads (Fp1/Fp2). This artifact can be mistaken for photic driving due to the synchrony with the stimuli. The source maybe the retina (ERG) or from a nonphysiologic source such as a frontopolar electrode with high impedance creating a photo-cell. Covering the eye with a towel will block the input to the retina (ERG) and this should not be confused with the photo-electric effect ( Tyner et al., 1983 ). The alpha rhythm may occasionally extend slightly into the superior frontal leads (F3, F4). Extension into the fronto-polar region (Fp1, Fp2) is practically unheard of. Apparent alpha rhythm in the fronto-polar leads may be very prominent in referential (unipolar) montages if the referential ear electrode picks up the posterior alpha rhythm. This is particularly com-mon when the mastoid region is used instead of the ear lobe (the mastoid being a preferred place with paste technique) ( Niedermeyer’s Electroencephalography ). Fronto-polar or orbito-frontal onset of seizures may be recorded from fronto-polar electrodes, and better resolved by supera-orbital or infra-orbital electrodes, sometimes it’s been referenced to midline electrodes like electrode on nose/chin, Fz, Cz or Pz. It is not uncommon for bilateral synchrony to occur in frontal lobe epilepsy ( Atlas of EEG, 2013 ). Subtle lateralization may be present with bilateral synchronous activity, mainly during sleep. This lateralization could be misleading. Absence of any ictal or immediate post ictal slowing has been reported in patient with mesial frontal lobe epilepsy ( Bautista et al., 1998 ). Behavioral manifestations with normal interictal EEG encountered in frontal lobe epilepsy may be misdiagnosed as psychogenic nonepileptic seizures. It emphasizes the need for early video-EEG monitoring in ambiguous cases before starting or modifying AED treatment.

Detrended fluctuation analysis for major depressive disorder.

Clinical utility of Electroencephalography (EEG) based diagnostic studies is less clear for major depressive disorder (MDD). In this paper, a novel machine learning (ML) scheme was presented to discriminate the MDD patients and healthy controls. The proposed method inherently involved feature extraction, selection, classification and validation. The EEG data acquisition involved eyes closed (EC) and eyes open (EO) conditions. At feature extraction stage, the de-trended fluctuation analysis (DFA) was performed, based on the EEG data, to achieve scaling exponents. The DFA was performed to analyzes the presence or absence of long-range temporal correlations (LRTC) in the recorded EEG data. The scaling exponents were used as input features to our proposed system. At feature selection stage, 3 different techniques were used for comparison purposes. Logistic regression (LR) classifier was employed. The method was validated by a 10-fold cross-validation. As results, we have observed that the effect of 3 different reference montages on the computed features. The proposed method employed 3 different types of feature selection techniques for comparison purposes as well. The results show that the DFA analysis performed better in LE data compared with the IR and AR data. In addition, during Wilcoxon ranking, the AR performed better than LE and IR. Based on the results, it was concluded that the DFA provided useful information to discriminate the MDD patients and with further validation can be employed in clinics for diagnosis of MDD.

Transition dynamics of EEG-based network microstates during mental arithmetic and resting wakefulness reflects task-related modulations and developmental changes.

We studied how maturation influences the organization of functional brain networks engaged during mental calculations and in resting state. Surface EEG measurements from 20 children (8-12years) and 25 students (21-26years) were analyzed. Interregional synchronization of brain activity was quantified by means of Phase Lag Index and for various frequency bands. Based on these pairwise estimates of functional connectivity, we formed graphs which were then characterized in terms of local structure [local efficiency (LE)] and overall integration (global efficiency). The overall data analytic scheme was applied twice, in a static and time-varying mode. Our results showed a characteristic trend: functional segregation dominates the network organization of younger brains. Moreover, in childhood, the overall functional network possesses more prominent small-world network characteristics than in early acorrect in xmldulthood in accordance with the Neural Efficiency Hypothesis. The above trends were intensified by the time-varying approach and identified for the whole set of tested frequency bands (from δ to low γ). By mapping the time-indexed connectivity patterns to multivariate timeseries of nodal LE measurements, we carried out an elaborate study of the functional segregation dynamics and demonstrated that the underlying network undergoes transitions between a restricted number of stable states, that can be thought of as "network-level microstates". The rate of these transitions provided a robust marker of developmental and task-induced alterations, that was found to be insensitive to reference montage and independent component analysis denoising.

Polysomnography using abbreviated signal montages: impact on sleep and cortical arousal scoring

ObjectiveThis study examined the impact of using two abbreviated signal montages on the accuracy, precision and inter-scorer reliability of polysomnography (PSG) sleep and arousal scoring, compared to a standard reference montage, in a cohort of patients investigated for obstructive sleep apnoea (OSA). One abbreviated montage incorporated two signals dedicated to sleep and arousal scoring, and the other incorporated a single signal. MethodsFour scorers from two laboratories each scored 15 PSGS four times in random order: once using each abbreviated montage and twice using the reference montage. ResultsUse of the two-signal montage resulted in small changes in the distribution of sleep stages, a reduction in the arousal index and resultant reductions in sleep and arousal scoring agreement. For the one-signal montage, although similar magnitude sleep stage distribution changes were observed, there were larger reductions in the arousal index, and sleep and arousal scoring accuracy. Additionally, using the one-signal montage, there were statistically significant reductions in the precision of summary statistics including total sleep time (TST) and the amount of rapid eye movement (REM) sleep scored, and reductions in the inter-scorer reliability of REM sleep and arousal scoring. ConclusionsThese findings demonstrate that abbreviated signal montages may result in underestimation of the arousal index and, depending on the montage, poorer precision in TST and REM sleep scoring, with potential consequences for apnoea–hypopnoea index (AHI) measures and OSA diagnosis. The results highlight the importance of careful evaluation of PSG results when using portable devices that have restricted signals, and they offer guidance for future PSG and portable monitoring standards.

Topographic distribution of EEG alpha attractor correlation dimension values in wake and drowsy states in humans

Organization of resting state cortical networks is of fundamental importance for the phenomenon of awareness, which is altered in the first part of hypnagogic period (Hori stages 1–4). Our aim was to investigate the change in brain topography pattern of EEG alpha attractor correlation dimension (CD) in the period of transition from Hori stage 1 to 4. EEG of ten healthy adult individuals was recorded in the wake and drowsy states, using a 14 channel average reference montage, from which 91 bipolar channels were derived and filtered in the wider alpha (6–14Hz) range. Sixty 1s long epochs of each state and individual were subjected to CD calculation according to the Grassberger–Procaccia method. For such a collection of signals, two embedding dimensions, d={5, 10}, and 22 time delays τ=2–23 samples were explored. Optimal values were d=10 and τ=18, where both saturation and second zero crossing of the autocorrelation function occurred. Bipolar channel CD underwent a significant decrease during the transition and showed a positive linear correlation with electrode distance, stronger in the wake individuals. Topographic distribution of bipolar channels with above median CD changed from longitudinal anterior–posterior pattern (awake) to a more diagonal pattern, with localization in posterior regions (drowsiness). Our data are in line with the literature reporting functional segregation of neuronal assemblies in anterior and posterior regions during this transition. Our results should contribute to understanding of complex reorganization of the cortical part of alpha generators during the wake/drowsy transition.

Automated localization of the seizure focus using interictal intracranial EEG.

Up to 30% of epileptic patients have seizures poorly controlled with anti-epileptic drugs alone. Surgical therapy might be beneficial to patients who respond poorly to drug treatments. It is therefore crucial to accurately localize the seizure focus. Neurologists rely heavily on seizures to determine the focus. The invasive recordings usually continue for days or weeks, which is costly and entails significant risk for the patients. In this paper, techniques are developed to localize the seizure focus using brief interictal intracranial EEG (iEEG). A supervised learning paradigm is utilized making use of features extracted from interictal iEEG on multiple referential montages. Analysis of 14 epileptic patients (implanted with depth electrodes) shows that iEEG features such as slowing, ripples, spikes, and local synchrony measures are strongly correlated to the seizure focus. These procedures may allow reliable localization of the seizure focus from brief interictal iEEG, which in turn may lead to shorter hospitalizations.

Should it matter when we record? Time of year and time of day as factors influencing frontal EEG asymmetry

Resting frontal encephalographic (EEG) asymmetry, often conceptualized as a trait marker for depression, is influenced by occasion-specific factors, including time of year and the time of day of the recording session as demonstrated recently (Peterson and Harmon-Jones, 2009). The current study examined the influence of seasonal and chronological variables on resting frontal asymmetry, and also assessed whether different reference montages or surface transformations were equally susceptible to these influences. In a direct replication attempt, contrary to previous findings, no simple time of year by time of day interaction was found. Time awake at recording, however, was an important moderating variable of the relationship between photoperiod and time of day. EEG asymmetry scores based on current-source density (CSD) transformed data, however, appeared less vulnerable to these influences, providing further evidence to suggest that the CSD transform may be advantageous for examining stable trait estimates of frontal EEG asymmetry.

Do sphenoidal electrodes aid in surgical decision making in drug resistant temporal lobe epilepsy?

ObjectiveThe utility of sphenoidal electrodes (SPh) in analyzing interictal epileptiform discharges (IEDs) and ictal electrography remains controversial, despite its widespread use. MethodsOne hundred and twenty-two consecutive patients with presumed temporal lobe epilepsy (TLE) who underwent presurgical evaluation were prospectively studied. SPh and Silverman’s electrodes were placed, in addition to routine electrodes in 10–20 international system. IEDs and ictal electroencephalography (EEG) were analyzed separately in bipolar and referential montages. The proportion of patients selected for surgery after adjusting for SPh placement based on the earlier ictal onset and IEDs were analyzed. ResultsOf the 8701 IEDs in SPh, only 65% were seen over the scalp bipolar montage; 1392 (16%) IEDs were confined to SPh electrodes, and were not seen at scalp bipolar montage (p<0.001). Spike amplitudes were highest at SPh (p<0.001). Of the 592 seizures analyzed, 62 (61%) had simultaneous SPh and scalp onset, while in 26 (25%) SPh onset preceded the scalp. ConclusionsOut of the 35 patients with unilateral mesial temporal sclerosis (MTS) with additional neocortical changes and/or non-lateralized bitemporal IEDs and/or diffuse ictal onset (group 1), 27 were selected for surgery (77%). About 7% was selected for surgery in this group by SPh placement. Also, in patients with bilateral MTS (group 2), 25% (5/20) were chosen for anterior temporal lobectomy, SPh provided an additional benefit in 11% (p<0.001). Patients with normal magnetic resonance imaging (group 3) and temporal plus epilepsy (group 4) had a lower surgical yield, only 12% and 9.5% could undergo surgery. They were denied surgical candidacy with SPh (p<0.001). SignificanceOne-third of patients after SPh placement were selected for resective surgery obviating the need for invasive monitoring. The maximum yield was noted in unilateral MTS (associated with additional neocortical features or non-lateralized bilateral temporal interictal IEDs or diffuse ictal onset in scalp EEG) and in bilateral MTS. Those with normal MRI/temporal plus epilepsy could be excluded from direct resective surgery.

The study and date analysis of interictal electroencephalogram in epileptic patients

The modern anticonvulsants can imitate normalization of clinical futures in epileptic children and change the typical epileptiform pattern of electroencephalogram (EEG). For this reason the correct evaluation of EEG in interictal period gain a special significance for adequate treatment strategy. The aim of this study was to elaborate the criteria for evolution of interictal EEG patterns using a computer EEG approach. EEG permits to study the correlation between clinical and neurophysiological outcomes making this technique useful not only for monitoring the course of the treatment but also for predicting the degree of tolerance and evaluating probable side effects, which is very important for revealing the possible early predictors of benefit/adverse effects of the treatment and for optimizing the anti-epileptic therapy. This study was aimed at investigating the alteration of different EEG characteristics in epilepsy contingent upon the treatment. The quantitative analysis of power spectrum of all frequencies of EEG potentials was analyzed. EEG signals were digitally recorded using a set of 19 scalp electrodes according to the International 10–20 system and ANCEPHALAN 131-03, professional version “MEDICOM”. For the statistical evaluation, the EEG phenomena were calculated within 6 frequency bands. The following quantitative characteristics of the EEGs were analyzed: 1) the pattern of native EEG with monopolar, bipolar and common average reference montage recordings for the evaluation of the specificity of the background activity, 2) absolute values of the power spectra, 3) mapping of the EEG spectral characteristics (topography). Qualitative assessment of the following EEG characteristics was performed: 1) interictal epileptiform abnormalities–with this the spike density and the number of paroxysmal discharges, 2) characteristics of alpha activity, 3) characteristics of beta activity. 137 patients with different forms of epilepsy, aged 3 to 12 years were examined. During the observation all patients received different types of anticonvulsants.

Frontal EEG asymmetry during emotional challenge differentiates individuals with and without lifetime major depressive disorder

Background Although it has been argued that frontal electroencephalographic (EEG) asymmetry at rest may be a risk marker for major depressive disorder (MDD), it is unclear whether a pattern of relatively less left than right activity characterizes depressed individuals during emotional challenges. Examination of frontal asymmetry during emotion task manipulations could provide an assessment of the function of systems relevant for MDD, and test the limits of frontal EEG asymmetry as a marker of risk for depression. Methods EEG data were assessed during a facial emotion task, wherein 306 individuals age 18–34 (31% male) with ( n = 143) and without ( n = 163) DSM-IV defined lifetime MDD made directed facial actions of approach (angry and happy) and withdrawal (afraid and sad) expressions. Results Lifetime depressed individuals displayed less relative left frontal activity than never-depressed individuals during all facial expressions across four EEG reference montages, findings that were not due to emotional experience, facial expression quality, electromyographic (EMG) activity, or current depression status. Limitations Although this was a sizable sample, only one emotion task was utilized. Conclusions Results provide further support for frontal EEG asymmetry as a risk marker for MDD.

EEG montage analysis in the Blind Source Separation framework

Blind Source Separation (BSS) is a relatively recent technique, more and more applied in electroencephalographic (EEG) signal processing. Still, the classical mixing model of the BSS does not take into account the real recording set-up. In fact, a major problem in electrophysiological recording systems (e.g. ECG, EEG, EMG) is to find a region in the human body whose bio-potential activity can be considered as neutral as possible i.e., a quasi-inactive reference place. Nowadays, it is well known that it is impossible to find a “zero-potential” site on the human body. In particular, the most common way of performing EEG recordings is by using as a common reference an electrode placed somewhere on the head. Starting from this Common Reference Montage (CRM), several other montages can be constructed to obtain alternative interpretation or processing solutions. Regardless of the chosen montage, the reference electrode intervenes in the mixing model of the BSS. The objective of this work is to analyse the influence of the montage on the mixing matrix and the quality of the BSS solution. This paper proposes to formalize the source separation problem in a non zero-potential reference context and shows that the Average Reference Montage (ARM), augmented by a virtual “average measure”, leads to better source separation results (separability index IS). This conclusion is supported by simulated EEGs using the most common montages i.e., Common Reference Montage, Average Reference Montage and Bipolar-Longitudinal Montage, as well as by real EEG examples.

704 CHANGE IN CEREBRAL ACTIVITY IN SEXUAL AROUSAL STATE BY SELECTIVE SEROTONIN REUPTAKE INHIBITOR ADMINISTRATION TO PREMATURE EJACULATION PATIENT: AN ANALYSIS USING LORETA (LOW RESOLUTION BRAIN ELECTROMAGNETIC TOMOGRAPHY)

You have accessJournal of UrologySexual Function/Dysfunction/Andrology: Basic Research I1 Apr 2010704 CHANGE IN CEREBRAL ACTIVITY IN SEXUAL AROUSAL STATE BY SELECTIVE SEROTONIN REUPTAKE INHIBITOR ADMINISTRATION TO PREMATURE EJACULATION PATIENT: AN ANALYSIS USING LORETA (LOW RESOLUTION BRAIN ELECTROMAGNETIC TOMOGRAPHY) Sung Chul Kam, Jae Hun Jung, and Jae Seog Hyun Sung Chul KamSung Chul Kam More articles by this author , Jae Hun JungJae Hun Jung More articles by this author , and Jae Seog HyunJae Seog Hyun More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.1145AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES To know the effects of serotonin reuptake inhibitor (SSRI) for the treatment of premature ejaculation (PE), changes of regional brain electrical activities by audiovisual erotic stimuli after sertraline administration were investigated utilizing three-dimensional electroencephalography (EEG) tomography. METHODS The eleven PE patients (36.9±7.8 yrs) and eleven male volunteers (24.2±1.9 yrs) were enrolled in this study. All recordings of EEG were done using international 10-20 system (23 channels). The EEGs were recorded during resting, watching a music-video, intermission and watching a porno-video before sertraline intake (control). EEG recordings were done 4 h after 50mg sertraline intake in the same order. Each segment was recorded for 10 min respectively. Five artifact-free segments with the average referential montage were selected. The LORETA images of cross-spectral analysis were obtained using the segments by LORETA-KEY software. Statistical nonparametric maps were obtained to detect the current density (CD) changes of high frequency bands between two EEG of control and 4 h after drug administration in each group. RESULTS Comparisons between control (before) and 4 h after drug intake in music video session of PE patients, the CD of beta-1 band were increased in Lt. fusiform gyrus and ligual gyrus. The CD of beta-2 band were decreased in Rt. superior temporal gyrus, inferior parietal lobule and precuneus. The CD of beta-3 band were increased in Rt. superior frontal gyrus and decreased in Rt. postcentral gyrus and fusiform gyrus. But comparisons between control and 4 h after drug intake in erotic video session of PE patients, the CD of beta-1 band were increased in Rt. middle temporal gyrus. And the CD of beta-3 band were increased in both superior frontal gyrus. Comparisons between PE patients and normal volunteers of 4 h after drug intake in erotic video session, the CD of beta-1 band were decreased in right middle temporal, superior temporal and middle occipital gyrus of PE patients. The CD of beta-2 band were decreased in Rt. middle occipital and lingual gyrus of PE patients. The CD of beta-3 band were decreased in Rt. middle and superior gyrus. CONCLUSIONS SSRI administration increased current source densities in both superior frontal and Rt. middle temporal gyrus in PE patients. It is suggested that SSRI acts on these particular cerebral regions and play an important role in the control of ejaculation on PE patients. Jinju, Republic of Korea© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e275 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Sung Chul Kam More articles by this author Jae Hun Jung More articles by this author Jae Seog Hyun More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Modulation by EEG features of BOLD responses to interictal epileptiform discharges

Introduction. EEG-fMRI of interictal epileptiform discharges (IEDs) usually assumes a fixed hemodynamic response function (HRF). This study investigates HRF variability with respect to IED amplitude fluctuations using independent component analysis (ICA), with the goal of improving the specificity of EEG-fMRI analyses. Methods. We selected EEG-fMRI data from 10 focal epilepsy patients with a good quality EEG. IED amplitudes were calculated in an average reference montage. The fMRI data were decomposed by ICA and a deconvolution method identified IED-related components by detecting time courses with a significant HRF time-locked to the IEDs (F-test, p<0.05). Individual HRF amplitudes were then calculated for each IED. Components with a significant HRF/IED amplitude correlation (Spearman test, p<0.05) were compared to the presumed epileptogenic focus and to results of a general linear model (GLM) analysis. Results. In 7 patients, at least one IED-related component was concordant with the focus, but many IED-related components were at distant locations. When considering only components with a significant HRF/IED amplitude correlation, distant components could be discarded, significantly increasing the relative proportion of activated voxels in the focus (p=0.02). In the 3 patients without concordant IED-related components, no HRF/IED amplitude correlations were detected inside the brain. Integrating IED-related amplitudes in the GLM significantly improved fMRI signal modeling in the epileptogenic focus in 4 patients (p<0.05). Conclusion. Activations in the epileptogenic focus appear to show significant correlations between HRF and IED amplitudes, unlike distant responses. These correlations could be integrated in the analysis to increase the specificity of EEG-fMRI studies in epilepsy.

Quantitative EEG Abnormalities are Associated With Memory Impairment in Recently Abstinent Methamphetamine-Dependent Individuals

Quantitative EEG Abnormalities are Associated With Memory Impairment in Recently Abstinent Methamphetamine-Dependent Individuals

EEG spectral changes underlying BOLD responses contralateral to spikes in patients with focal epilepsy

Simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) in patients with focal epilepsy and unilateral spikes often shows positive blood oxygenation level-dependent (BOLD) responses (activations), not only ipsilateral but also contralateral to the spikes. We aimed to investigate whether minimal EEG changes could underlie these contralateral BOLD responses by using EEG spectral analysis. We studied 19 patients with focal epilepsy and unilateral spikes. According to the pattern of BOLD activation, patients were divided into Group 1 (ipsi- and contralateral to the spikes) or Group 2 (only ipsilateral). EEG from outside the scanner was used to mark spikes similar to those recorded in the scanner. Epochs of 640 ms before and after the peak of the spikes were chosen as baseline and spike epochs. Spectral analysis was performed in referential montage (FCz reference), and differences between baselines and spikes were analyzed by paired t-test. Significant EEG changes in electrodes contralateral to the spikes were seen in 9 of 10 patients in Group 1 and in only 2 of 10 patients in Group 2 (one patient had two types of spikes that were analyzed separately). Spectral changes were seen in delta and/or theta bands in all patients except one (in Group 1) who had changes in all bands. Significant contralateral EEG changes occurred in 90% of contralateral BOLD activations and in only 20% of patients without contralateral BOLD responses. The reason why these changes predominate in lower frequencies rather than in higher frequencies is unclear. These spectral changes in areas corresponding to contralateral activations might reflect poorly synchronized but possibly intense neuronal activity.

ELECTROCLINICAL CHARACTERISTICS OF MICTURITION-INDUCED REFLEX EPILEPSY

In this Teaching Video Neuro Image , Rathore et al.1 infer that a possible restricted midline epileptogenic focus based on observed ictal electroencephalography (EEG) activity was “confined to the Cz electrode.” The ictal activity seen in the figure appears to be limited to the Cz electrode. EEG is displayed using the common average montage, a referential montage that shows an ictal “beta burst” at the Cz electrode (without clear reflection at the adjacent scalp electrodes: C3, C4, Fz, Pz) and only lasting for <1 sec (as seen in the 10-sec EEG page of the accompanying Video Neuro Image ). There appears to …