Home About us Contact | |||
Scalp Electrodes (scalp + electrode)
Selected AbstractsFetal heart rate patterns and ECG ST segment changes preceding metabolic acidaemia at birthBJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 2 2005Isis Amer-Wåhlin Objectives To compare the rates of abnormal ST segment patterns of the ECG and cardiotocographic (CTG) abnormalities in fetuses with metabolic acidaemia at birth and controls. To evaluate the inter-observer agreement in interpretation of ST analysis and CTG. Design Case,control study. Setting Three University hospitals in southern Sweden. Population Cases and controls were selected from the Swedish randomised controlled trial on intrapartum monitoring, including 4966 fetuses monitored with a scalp electrode. Methods Two obstetricians independently assessed the CTG and ST traces of 41 fetuses with metabolic acidaemia at birth and 101 controls, blinded to group, outcome and all clinical data. They classified each CTG trace and ST analysis as abnormal or not abnormal, and whether there was indication to intervene according to the CTG or to the CTG + ST guidelines. If their classification differed, assessment by a third obstetrician determined the final classification. Main outcome measures Rates of CTG and ST abnormalities and decisions to intervene. Rates of inter-observer agreement. Results CTG was classified as abnormal in 50% and ST in 63% of cases with acidaemia, and in 20% and 34% of controls, respectively. CTG abnormalities were judged to be indication for intervention in 45% and CTG + ST abnormalities in 56% of cases with acidaemia, and in 15% and 8% of controls, respectively. The proportion of agreement between the two initial observers was significantly higher for ST abnormalities (94%) than for CTG abnormalities (73%), and for indication to intervene according to CTG + ST (89%) than according to CTG alone (76%). Conclusions The inter-observer agreement rate was higher for a decision to intervene based on CTG + ST than on CTG alone. [source] Dense array EEG: Methodology and new hypothesis on epilepsy syndromesEPILEPSIA, Issue 2008Mark D. Holmes Summary Dense array EEG is a method of recording electroencephalography (EEG) with many more electrodes (up to 256) than is utilized with standard techniques that typically employ 19,21 scalp electrodes. The rationale for this approach is to enhance the spatial resolution of scalp EEG. In our research, dense array EEG is used in conjunction with a realistic model of head tissue conductivity and methods of electrographic source analysis to determine cerebral cortical localization of epileptiform discharges. In studies of patients with absence seizures, only localized cortical regions are involved during the attack. Typically, absences are accompanied by "wave,spike" complexes that show, both at the beginning and throughout the ictus, repetitive cycles of stereotyped, localized involvement of mainly mesial and orbital frontal cortex. Dense array EEG can also be used for long-term EEG video monitoring (LTM). We have used dense array EEG LTM to capture seizures in over 40 patients with medically refractory localization-related epilepsy, including both temporal and extra temporal cases, where standard LTM failed to reveal reliable ictal localization. One research goal is to test the validity of dense array LTM findings by comparison with invasive LTM and surgical outcome. Collection of a prospective series of surgical candidates who undergo both procedures is currently underway. Analysis of subjects with either generalized or localization-related seizures suggest that all seizures, including those traditionally classified as "generalized," propagate through discrete cortical networks. Furthermore, based on initial review of propagation patterns, we hypothesize that all epileptic seizures may be fundamentally corticothalamic or corticolimbic in nature. Dense array EEG may prove useful in noninvasive ictal localization, when standard methods fail. Future research will determine if the method will reduce the need for invasive EEG recordings, or assist in the appropriate placement of novel treatment devices. [source] Lateralizing and Localizing Values of Ictal Onset Recorded on the Scalp: Evidence from Simultaneous Recordings with Intracranial Foramen Ovale ElectrodesEPILEPSIA, Issue 11 2001G. Alarcón Summary: ,Purpose: The value of scalp recordings to localize and lateralize seizure onset in temporal lobe epilepsy has been assessed by comparing simultaneous scalp and intracranial foramen ovale (FO) recordings during presurgical assessment. The sensitivity of scalp recordings for detecting mesial temporal ictal onset has been compared with a "gold standard" provided by simultaneous deep intracranial FO recordings from the mesial aspect of the temporal lobe. As FO electrodes are introduced via anatomic holes, they provide a unique opportunity to record simultaneously from scalp and mesial temporal structures without disrupting the conducting properties of the brain coverings by burr holes and wounds, which can otherwise make simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG. Methods: Simultaneous FO and scalp recordings from 314 seizures have been studied in 110 patients under telemetric presurgical assessment for temporal lobe epilepsy. Seizure onset was identified on scalp records while blind to recordings from FO electrodes and vice versa. Results: Bilateral onset (symmetric or asymmetric) was more commonly found in scalp than in FO recordings. The contrary was true for unilateral seizure onset. In seizures with bilateral asymmetric onset on the scalp, the topography of largest-amplitude scalp changes at onset does not have localizing or lateralizing value. However, 75,76% of seizures showing unilateral scalp onset with largest amplitude at T1/T2 or T3/T4 had mesial temporal onset. This proportion dropped to 42% among all seizures with a unilateral scalp onset at other locations. Of those seizures with unilateral onset on the scalp at T1/T2, 65.2% showed an ipsilateral mesial temporal onset, and 10.9% had scalp onset incorrectly lateralized with respect to the mesial temporal onset seen on FO recordings. In seizures with a unilateral onset on the scalp at electrodes other than T1/T2, the proportions of seizures with correctly and incorrectly lateralized mesial temporal onset were 37.5 and 4.2%, respectively. Thus the ratio between incorrectly and correctly lateralized mesial temporal onsets is largely similar for seizures with unilateral scalp onset at T1/T2 (16.7%) and for seizures with unilateral scalp onset at electrodes other than T1/T2 (11.2%). The onset of scalp changes before the onset of clinical manifestations is not associated with a lower proportion of seizures with bilateral onset on the scalp, or with a higher percentage of mesial temporal seizures or of mesial temporal seizures starting ipsilateral to the side of scalp onset. In contrast, the majority (78.4%) of mesial temporal seizures showed clinical manifestations starting after ictal onset on FO recordings. Conclusions: A bilateral scalp onset (symmetric or asymmetric) is compatible with a mesial temporal onset, and should not deter further surgical assessment. Although a unilateral scalp onset at T1/T2 or T3/T4 is associated with a higher probability of mesial temporal onset, a unilateral onset at other scalp electrodes does not exclude mesial temporal onset. A unilateral scalp onset at electrodes other than T1/T2 is less likely to be associated with mesial temporal onset, but its lateralizing value is similar to that of unilateral scalp onset at T1/T2. The presence of clinical manifestations preceding scalp onset does not reduce the localizing or lateralizing values of scalp recordings. [source] Event-related delta oscillatory responses of Alzheimer patientsEUROPEAN JOURNAL OF NEUROLOGY, Issue 6 2008G. Yener Background and purpose:, Alzheimer type of dementia (AD) is the most common neuropsychiatric morbidity in elderly individuals. Event-related oscillations (ERO) provide an useful tool for detecting subtle abnormalities of cognitive processes with high temporal resolution. Methods:, In the present report, event-related oscillations of patients with AD were analyzed by using a visual oddball paradigm. A total of 22 mild probable AD subjects according to NINCDS-ADRDA criteria and 20 age-, gender-, and education-matched healthy control subjects were compared. AD group consisted from 11 untreated patients and 11 patients treated with cholinesterase inhibitor. Oscillatory responses were recorded from 13 scalp electrodes. Results:, Significant differences in delta frequency range were seen between the groups by using repeated measures of anova analysis [F(9.120) = 2.228; P = 0.022]. Post-hoc analyses using Wilcoxon test showed that at mid- and left central regions, (Cz, C3) peak amplitudes of delta responses of healthy subjects were significantly higher than either group. Also cholinesterase inhibitors did not have effect on delta oscillatory responses. Conclusions:, Our findings imply that the delta oscillatory responses at central locations are highly instable in mild probable AD patients regardless of treatment when compared to the healthy aged controls. This study supports the importance of oscillatory event-related potentials for investigating AD brain dynamics. [source] The effect of stimulus intensity on brain responses evoked by transcranial magnetic stimulationHUMAN BRAIN MAPPING, Issue 3 2004Soile Komssi Abstract To better understand the neuronal effects of transcranial magnetic stimulation (TMS), we studied how the TMS-evoked brain responses depend on stimulation intensity. We measured electroencephalographic (EEG) responses to motor-cortex TMS, estimated the intensity dependence of the overall brain response, and compared it to a theoretical model for the intensity dependence of the TMS-evoked neuronal activity. Left and right motor cortices of seven volunteers were stimulated at intensities of 60, 80, 100, and 120% of the motor threshold (MT). A figure-of-eight coil (diameter of each loop 4 cm) was used for focal stimulation. EEG was recorded with 60 scalp electrodes. The intensity of 60% of MT was sufficient to produce a distinct global mean field amplitude (GMFA) waveform in all subjects. The GMFA, reflecting the overall brain response, was composed of four peaks, appearing at 15 ± 5 msec (Peak I), 44 ± 10 msec (II), 102 ± 18 msec (III), and 185 ± 13 msec (IV). The peak amplitudes depended nonlinearly on intensity. This nonlinearity was most pronounced for Peaks I and II, whose amplitudes appeared to sample the initial part of the sigmoid-shaped curve modeling the strength of TMS-evoked neuronal activity. Although the response amplitude increased with stimulus intensity, scalp distributions of the potential were relatively similar for the four intensities. The results imply that TMS is able to evoke measurable brain activity at low stimulus intensities, probably significantly below 60% of MT. The shape of the response-stimulus intensity curve may be an indicator of the activation state of the brain. Hum. Brain Mapp. 21:154,164, 2004. © 2004 Wiley-Liss, Inc. [source] Binge Drinking Affects Attentional and Visual Working Memory Processing in Young University StudentsALCOHOLISM, Issue 11 2009Alberto Crego Background:, Binge Drinking (BD) typically involves heavy drinking over a short time, followed by a period of abstinence, and is common among young people, especially university students. Animal studies have demonstrated that this type of alcohol consumption causes brain damage, especially in the nonmature brain. The aim of the present study was to determine how BD affects brain functioning in male and female university students, during the performance of a visual working memory task. Methods:, Event-related potentials (ERPs) were recorded, with an extensive set of 32 scalp electrodes, in 95 first-year university students (age range 18 to 20 years), comprising 42 binge drinkers (BD) and 53 controls, in a visual "identical pairs" continuous performance task. Principal components analysis was used to identify and analyze the N2 (negative waveform with a latency around 200 to 300 ms related to attentional processes) and P3 (positive waveform with a latency around 300 to 600 ms related to working memory processes) components of the ERPs. Results:, In the matching condition of the task, the N2 component in central and parietal regions was significantly larger in the BD than in the control group. In the control group, the P3 component was larger in the matching than in the nonmatching condition in the frontal, central, and parietal regions, whereas the BD group did not show any significant differences between conditions in any region. Conclusions:, The results of this study confirm the presence of electrophysiological differences between young university student binge drinkers and controls during the execution of a visual task with a high working memory load. The larger N2 in the BD group suggests higher levels of attentional effort required by this group to perform the task adequately. The absence of any differences in the P3 component in the different conditions (matching and nonmatching stimuli) in the BD group suggests a deficiency in the electrophysiological differentiation between relevant and irrelevant information, which may reflect some impairment of working memory processes. [source] Cortical locations of maximal spindle activity: magnetoencephalography (MEG) studyJOURNAL OF SLEEP RESEARCH, Issue 2 2009VALENTINA GUMENYUK Summary The aim of this study was to determine the main cortical regions related to maximal spindle activity of sleep stage 2 in healthy individual subjects during a brief morning nap using magnetoencephalography (MEG). Eight volunteers (mean age: 26.1 ± 8.7, six women) all right handed, free of any medical psychiatric or sleep disorders were studied. Whole-head 148-channel MEG and a conventional polysomnography montage (EEG; C3, C4, O1 and O2 scalp electrodes and EOG, EMG and ECG electrodes) were used for data collection. Sleep MEG/EEG spindles were visually identified during 15 min of stage 2 sleep for each participant. The distribution of brain activity corresponding to each spindle was calculated using a combination of independent component analysis and a current source density technique superimposed upon individual MRIs. The absolute maximum of spindle activation was localized to frontal, temporal and parietal lobes. However, the most common cortical regions for maximal source spindle activity were precentral and/or postcentral areas across all individuals. The present study suggests that maximal spindle activity localized to these two regions may represent a single event for two types of spindle frequency: slow (at 12 Hz) and fast (at 14 Hz) within global thalamocortical coherence. [source] Working memory in posttraumatic stress disorder,an event-related potential studyJOURNAL OF TRAUMATIC STRESS, Issue 2 2001Cherrie Galletly Abstract This study examined ERP topography during the updating and the utilization of working memory in subjects with PTSD. Event-related potentials of 18 participants with PTSD and 18 controls were recorded from 32 scalp electrodes during an auditory target detection task requiring the constant updating of target identity. Midline N2 and P3 abnormalities previously noted in PTSD during target detection were replicated. Scalp topographic data revealed sustained reduction in activity over the right hemisphere during working memory updating. Executive processes were associated with brief but widespread right hemisphere reductions during the P3, followed by sustained, bilateral reduction frontally. This study identifies an abnormal pattern of cortical network function during both the updating and use of working memory in PTSD. [source] |