Analysis Of Scalp EEG Research Articles

Inter- and Intra-Hemispheric Age-Related Remodeling in Visuo-Spatial Working Memory.

Electroencephalography (EEG) studies investigating visuo-spatial working memory (vWM) in aging typically adopt an event-related potential (ERP) analysis approach that has shed light on the age-related changes during item retention and retrieval. However, this approach does not fully enable a detailed description of the time course of the neural dynamics related to aging. The most frequent age-related changes in brain activity have been described by two influential models of neurocognitive aging, the Hemispheric Asymmetry Reduction in Older Adults (HAROLD) and the Posterior-Anterior Shift in Aging (PASA). These models posit that older adults tend to recruit additional brain areas (bilateral as predicted by HAROLD and anterior as predicted by PASA) when performing several cognitive tasks. We tested younger (N = 36) and older adults (N = 35) in a typical vWM task (delayed match-to-sample) where participants have to retain items and then compare them to a sample. Through a data-driven whole scalp EEG analysis we aimed at characterizing the temporal dynamics of the age-related activations predicted by the two models, both across and within different stages of stimulus processing. Behaviorally, younger outperformed older adults. The EEG analysis showed that older adults engaged supplementary bilateral posterior and frontal sites when processing different levels of memory load, in line with both HAROLD and PASA-like activations. Interestingly, these age-related supplementary activations dynamically developed over time. Indeed, they varied across different stages of stimulus processing, with HAROLD-like modulations being mainly present during item retention, and PASA-like activity during both retention and retrieval. Overall, the present results suggest that age-related neural changes are not a phenomenon indiscriminately present throughout all levels of cognitive processing.

SCOPE-mTL: A non-invasive tool for identifying and lateralizing mesial temporal lobe seizures prior to scalp EEG ictal onset.

In mesial temporal lobe (mTL) epilepsy, seizure onset can precede the appearance of a scalp EEG ictal pattern by many seconds. The ability to identify this early, occult mTL seizure activity could improve lateralization and localization of mTL seizures on scalp EEG. Using scalp EEG spectral features and machine learning approaches on a dataset of combined scalp EEG and foramen ovale electrode recordings in patients with mTL epilepsy, we developed an algorithm, SCOPE-mTL, to detect and lateralize early, occult mTL seizure activity, prior to the appearance of a scalp EEG ictal pattern. Using SCOPE-mTL, 73% of seizures with occult mTL onset were identified as such, and no seizures that lacked an occult mTL onset were identified as having one. Predicted mTL seizure onset times were highly correlated with actual mTL seizure onset times (r=0.69). 50% of seizures with early mTL onset were lateralizable prior to scalp ictal onset, with 94% accuracy. SCOPE-mTL can identify and lateralize mTL seizures prior to scalp EEG ictal onset, with high sensitivity, specificity, and accuracy. Quantitative analysis of scalp EEG can provide important information about mTL seizures, even in the absence of a visible scalp EEG ictal correlate.

Analysis of scalp EEG and quantitative MRI in cases of temporal lobe epilepsy requiring intracranial electrographic monitoring

Purpose. Contradictory scalp electroencephalographic (sEEG) and discordant imaging features are common in temporal lobe epilepsy (TLE). We assessed the relative importance of sEEG features and their relation to quantitative magnetic resonance (MR) imaging measures in regard to surgical outcome. Methods and materials. Patients with a putative TLE underwent extraoperative electrocorticography (eECoG) with bitemporal subdural electrodes for clarification of the ictogenic source. Patients were categorized by sEEG ictal patterns (IPs) as showing unilateral or bilateral onset. Concordance with the side of resection, as determined by eECoG, to that suggested by the predominant sEEG IP was further analysed as: (a) entirely ipsilateral eECoG IPs with discordant nonelectrographic data; (b) ipsilateral preponderant (> 80%) eECoG IPs; and c) contralateral preponderant (> 80%) eECoG IPs. Quantitative hippocampal volumes and signal characteristics were applied for comparison. Results. Of 26 patients, eECoG confirmed a unilateral IP on sEEG in 19 (73%). Of these 19, exclusively ipsilateral sEEG interical epileptiform discharges (IEDs) were identified in 9 (47%). When bilateral, generalized, absent or contralateral IEDs were found, 6 cases (60%) still showed a preponderantly ipsilateral IP identifying the epileptogenic side. In patients with sEEG bilateral IPs, 5 (71%) also had bilateral IEDs. Of the 16 patients who underwent resection, 14 (87.5%) achieved favourable outcomes and 9 (56%), seizure cessation. Hippocampal volumetry in 23 patients correctly lateralized 7 (30%) whereas fluid-attenuated inversion recovery (FLAIR) signal measures applied in 23 patients lateralized 9 (39%). Conclusions. Favourable surgical outcomes are attainable following eECoG in cases where ambiguity exists regarding the laterality of TLE on sEEG, even for those in whom bilateral IPs and either bilateral or no IEDs are demonstrated on sEEG. Neither volumetric nor FLAIR signal ratios were sufficiently reliable for lateralizing TLE in the majority of cases.

EEG Observations in Elderly With New Onset Seizures

The authors evaluated the spectra of EEG observations in elderly patients with new onset seizures and correlated it with clinical, laboratory, and imaging findings. This prospective study involved 201 elderly individuals (age: 68.0 ± 7.5 years; male:female = 1.8:1) who manifested with new onset seizures. Data regarding clinical, laboratory, routine EEG (n = 201), and imaging (computerized tomography = 201; MRI = 43) observations were noted. Details of EEG findings were analyzed and correlated with other parameters. Visual analysis of scalp EEG in 124 patients (61.7%) was abnormal, and the abnormalities included asymmetric background activity (3%) and diffuse slowing (32.8%) and focal slowing (7%) of the background activity. Dominant α-activity was more common in remote symptomatic group. Higher frequency of alpha waves was observed in patients with cryptogenic epilepsy compared with those with acute symptomatic epilepsy. Diffuse slowing and excess of β-fast activity were observed more often in acute symptomatic group. Epileptiform activities were evident in one third of patients and were noted in the temporal (38.8%) and frontotemporal (23.9%) regions. In univariate analysis of patients with and without EEG abnormalities, female gender, cluster attacks/status epilepticus, acute symptomatic epilepsy, longer duration of postictal state, lower Glasgow coma scale score, lower Mini-Mental State Examination score, focal deficits, diffuse edema (computerized tomography), and focal lesions (MRI) were significantly associated with abnormal EEG. Presence of epileptiform activity predicted the use of polytherapy (P = 0.004, odds ratio = 3.3). The significant factors associated with an abnormal EEG (multivariate) were female gender (P = 0.03, odds ratio = 2.32), lower Glasgow coma scale score (P = 0.03, odds ratio = 0.70), and lower frequency of α-waves (P = 0.04, odds ratio = 0.56). Scalp EEG was abnormal in approximately two thirds of elderly patients, with the presence of epileptiform activities in one third of patients. Abnormal EEG significantly correlated with lower Glasgow coma scale score, suggesting its role in prognostication.

Multiple band frequency analysis in a child of medial temporal lobe ganglioglioma

We report a 1-year 6-month-old girl with ganglioglioma in the right medial temporal lobe who showed epileptic spasms in clusters. Spasms occasionally followed a dazed and fearful gaze. Interictal electroencephalography (EEG) showed diffuse bursts of slightly irregular high-voltage spikes and slow waves without hypsarrhythmia. The findings on ictal EEG, single-photon emission computed tomography, and F-18 fluorodeoxyglucose positron emission tomography indicated focus on the right medial temporal lobe. Ictal fast rhythmic activity analysis of scalp EEG by multiple band frequency analysis showed gamma rhythms at 65-80 Hz with a high spectral power around the tumor area. Epileptic spasms completely disappeared after tumor resection. These findings suggest that the cerebral cortex may be a source of epileptic spasms and indicate the possibility of usefulness of fast activity analysis in this condition.