Human MT/V5 activity on viewing eye gaze changes in others: A magnetoencephalographic study

The present study used magnetoencephalography (MEG) to investigate human MT/V5 activity when observing changes in eye gaze. Subjects viewed a face in which the eyes changed to look either directly at (BACK) or away from (AWAY) the subject in a series of apparent motion conditions. BACK involved 2 directions, from left to center (LC) and from right to center (RC). Likewise, AWAY involved 2 directions, from center to left (CL) and from center to right (CR). A clear MEG component, 1M, was elicited with all eye gaze changes. Mean peak latency was 157 ms and was unaffected by stimulus condition. The equivalent current dipole (ECD) was localized to human MT/V5. Two main effects were noted: (1) ECD moment was significantly larger for BACK than for AWAY; and (2) 1M ECD locations were more posterior for AWAY than for BACK. Gaze direction, with LEFT involving CL and RC and RIGHT involving CR and LC, showed no significant effects. These data indicate that MT/V5 responds to gaze direction rather than eye position, and that eye movements directed at the viewer elicit the strongest effects. Processing of gaze change is NOT sensitive to eye direction per se but rather is modulated by eye gaze relative to the viewer.     

Impaired pre-attentive auditory processing in opioid dependence with and without benzodiazepine co-dependence revealed by combined magnetoencephalography and electroencephalography

Cognitive dysfunctions may be a significant factor in drug-seeking behavior, reducing the efficiency of rehabilitation in opioid dependence. Neurophysiological basis of these dysfunctions is poorly understood. 21 opioid-dependent patients and 15 healthy controls with no experience of illicit drugs were studied with simultaneous electroencephalography (EEG) and magnetoencephalography (MEG). Among opioid dependents 15 were benzodiazepine co-dependent. In a passive oddball paradigm, a train of 700-Hz standard tones (80%), presented to the left ear, was occasionally interrupted by infrequent deviants, which were either 600-Hz or 400-Hz pure tones or complex novel sounds. The auditory evoked potentials (AEP) and fields (AEF) were analyzed. The strength of the N1m dipoles was enhanced in patients with benzodiazepine co-dependence, but the latency of the response or the source location was not changed. A delay of mismatch negativity (MMN) response of novel tones in EEG, and delay of P3am response on the contralateral hemisphere to stimulated ear in MEG in opioid-dependent patients were observed. There were no differences in source locations or strengths of the dipoles for P1m, MMNm, and P3am determined using equivalent current dipoles. There were no group differences in EEG amplitude measures. In conclusion, our results suggest delayed pre-attentive auditory processing of novel information in opioid dependence. Benzodiazepine co-dependence modulated N1m response.     

Automatic ictal onset source localization in presurgical epilepsy evaluation

Objective

To test the diagnostic accuracy of a new automatic algorithm for ictal onset source localization (IOSL) during routine presurgical epilepsy evaluation following STARD (Standards for Reporting of Diagnostic Accuracy) criteria.

Top-down effects on early visual processing in humans: a predictive coding framework

An increasing number of human electroencephalography (EEG) studies examining the earliest component of the visual evoked potential, the so-called C1, have cast doubts on the previously prevalent notion that this component is impermeable to top-down effects. This article reviews the original studies that (i) described the C1, (ii) linked it to primary visual cortex (V1) activity, and (iii) suggested that its electrophysiological characteristics are exclusively determined by low-level stimulus attributes, particularly the spatial position of the stimulus within the visual field. We then describe conflicting evidence from animal studies and human neuroimaging experiments and provide an overview of recent EEG and magnetoencephalography (MEG) work showing that initial V1 activity in humans may be strongly modulated by higher-level cognitive factors. Finally, we formulate a theoretical framework for understanding top-down effects on early visual processing in terms of predictive coding.     

Clinical utility of EEG in diagnosing and monitoring epilepsy in adults

Electroencephalography (EEG) remains an essential diagnostic tool for people with epilepsy (PWE). The International Federation of Clinical Neurophysiology produces new guidelines as an educational service for clinicians to address gaps in knowledge in clinical neurophysiology. The current guideline was prepared in response to gaps present in epilepsy-related neurophysiological assessment and is not intended to replace sound clinical judgement in the care of PWE. Furthermore, addressing specific pathophysiological conditions of the brain that produce epilepsy is of primary importance though is beyond the scope of this guideline. Instead, our goal is to summarize the scientific evidence for the utility of EEG when diagnosing and monitoring PWE.     

Epileptogenic high-frequency oscillations skip the motor area in children with multilobar drug-resistant epilepsy

Objective

Subtotal hemispherectomy involves the resection of multiple lobes in children with drug-resistant epilepsy, skipping the motor area (MA). We determined epileptogenicity using the occurrence rate (OR) of high-frequency oscillations (HFOs) and the modulation index (MI), demonstrating strength of coupling between HFO and slow wave. We hypothesized that epileptogenicity increased over the multiple lobes but skipped the MA.

An MRI study of the superior temporal subregions in patients with current and past major depression

The superior temporal gyrus (STG), especially its lateral portion, and temporal pole (TP) both play a central role in emotional processing, but it remains largely unknown whether patients with major depressive disorder (MDD) exhibit morphologic changes in these regions. We delineated the STG subregions [planum polare (PP), Heschl gyrus (HG), planum temporale (PT), rostral STG, and caudal STG] and TP using magnetic resonance imaging in 29 currently depressed patients (mean age = 32.5 years, 7 males), 27 remitted depressed patients (mean age = 35.1 years, 9 males), and 33 age- and gender-matched healthy control subjects (mean age = 34.0 years, 12 males). Both current and remitted MDD patients showed a significant volume reduction of the left PT and bilateral caudal STG as compared with healthy controls. The TP volume did not differ between the groups. The right PT volume was negatively correlated with total score on the Beck Depression Inventory in the MDD patients as a whole. Medication, presence of melancholia, and comorbidity with anxiety disorders did not affect the TP and STG volumes. These findings suggest that the volume reduction of the STG, but not the TP, may represent enduring brain changes in MDD even after recovery from depression, but right STG volume may also be related to the severity of depressive symptoms.     

Preattentive dysfunction in bipolar disorder: A MEG study using auditory mismatch negativity

Background

Neuropsychological studies have demonstrated that cognitive dysfunction represents pathophysiological mechanisms underlying bipolar disorder. However, information processing deficits in bipolar disorder have not often been examined electrophysiologically. Here, we examined preattentive processing and sensory information processing using mismatch field (MMNm) and P1m components, respectively, using magnetoencephalography.

Methods

Ten patients with bipolar disorder and 20 healthy volunteers participated in the study. The participants were presented with auditory stimuli sequences comprising standard and deviant stimuli. MMNm was elicited in response to changes in duration and frequency of pure-tone stimuli and a vowel across-category change.

Results

The magnetic global field power of MMNm in the right hemisphere under the pure-tone condition was significantly delayed in patients with bipolar disorder compared to healthy volunteers, and that of P1m did not differ between the two groups. The MMNm dipole in the left hemisphere was located inferior in patients with bipolar disorder than in healthy volunteers. This finding did not correlate with clinical symptoms.

Conclusions

Information processing at the preattentive level is impaired in patients with bipolar disorder irrespective of clinical symptoms, and this dysfunction is not due to sensory level dysfunction. The quality of preattentive information processing impairment is different between patients with bipolar disorder and patients with major depressive disorder, as shown by the MMNm latency and power differences.     

Clinical correlates of graph theory findings in temporal lobe epilepsy

PurposeTemporal lobe epilepsy (TLE) is considered a brain network disorder, additionally representing the most common form of pharmaco-resistant epilepsy in adults. There is increasing evidence that seizures in TLE arise from abnormal epileptogenic networks, which extend beyond the clinico-radiologically determined epileptogenic zone and may contribute to the failure rate of 30–50% following epilepsy surgery. Graph theory allows for a network-based representation of TLE brain networks using several neuroimaging and electrophysiologic modalities, and has potential to provide clinicians with clinically useful biomarkers for diagnostic and prognostic purposes.MethodsWe performed a review of the current state of graph theory findings in TLE as they pertain to localization of the epileptogenic zone, prediction of pre- and post-surgical seizure frequency and cognitive performance, and monitoring cognitive decline in TLE.ResultsAlthough different neuroimaging and electrophysiologic modalities have yielded occasionally conflicting results, several potential biomarkers have been characterized for identifying the epileptogenic zone, pre-/post-surgical seizure prediction, and assessing cognitive performance. For localization, graph theory measures of centrality have shown the most potential, including betweenness centrality, outdegree, and graph index complexity, whereas for prediction of seizure frequency, measures of synchronizability have shown the most potential. The utility of clustering coefficient and characteristic path length for assessing cognitive performance in TLE is also discussed.ConclusionsFuture studies integrating data from multiple modalities and testing predictive models are needed to clarify findings and develop graph theory for its clinical utility.     

Individual localization value of resting-state fMRI in epilepsy presurgical evaluation: A combined study with stereo-EEG

ObjectiveTo examine the individual-patient-level localization value of resting-state functional MRI (rsfMRI) metrics for the seizure onset zone (SOZ) defined by stereo-electroencephalography (SEEG) in patients with medically intractable focal epilepsies.MethodsWe retrospectively included 19 patients who underwent SEEG implantation for epilepsy presurgical evaluation. Voxel-wise whole-brain analysis was performed on 3.0 T rsfMRI to generate clusters for amplitude of low-frequency fluctuations (ALFF), regional homogeneity (ReHo) and degree centrality (DC), which were co-registered with the SEEG-defined SOZ to evaluate their spatial overlap. Subgroup and correlation analyses were conducted for various clinical characteristics.ResultsALFF demonstrated concordant clusters with SEEG-defined SOZ in 73.7% of patients, with 93.3% sensitivity and 77.8% PPV. The concordance rate showed no significant difference when subgrouped by lesional/non-lesional MRI, SOZ location, interictal epileptiform discharges on scalp EEG, pathology or seizure outcomes. No significant correlation was seen between ALFF concordance rate and epilepsy duration, seizure-onset age, seizure frequency or number of antiseizure medications. ReHo and DC did not achieve favorable concordance results (10.5% and 15.8%, respectively). All concordant clusters showed regional activation, representing increased neural activities.ConclusionALFF had high concordance rate with SEEG-defined SOZ at individual-patient level.SignificanceALFF activation on rsfMRI can add localizing information for the noninvasive presurgical workup of intractable focal epilepsies.     

Automated electrical source imaging with scalp EEG to define the insular irritative zone: Comparison with simultaneous intracranial EEG

Objective To evaluate the accuracy of automated interictal low-density electrical source imaging (LD-ESI) to define the insular irritative zone (IZ) by comparing the simultaneous interictal ESI localization with the SEEG interictal activity.Methods Long-term simultaneous scalp electroencephalography (EEG) and stereo-EEG (SEEG) with at least one depth electrode exploring the operculo-insular region(s) were analyzed. Automated interictal ESI was performed on the scalp EEG using standardized low-resolution brain electromagnetic tomography (sLORETA) and individual head models. A two-step analysis was performed: i) sublobar concordance between cluster-based ESI localization and SEEG-based IZ; ii) time-locked ESI-/SEEG analysis. Diagnostic accuracy values were calculated using SEEG as reference standard. Subgroup analysis was carried out, based on the involvement of insular contacts in the seizure onset and patterns of insular interictal activity.Results Thirty patients were included in the study. ESI showed an overall accuracy of 53% (C.I. 29–76%). Sensitivity and specificity were calculated as 53% (C.I. 29–76%), 55% (C.I. 23–83%) respectively. Higher accuracy was found in patients with frequent and dominant interictal insular spikes.Conclusions LD-ESI defines with good accuracy the insular implication in the IZ, which is not possible with classical interictal scalp EEG interpretation.SignificanceAutomated LD-ESI may be a valuable additional tool to characterize the epileptogenic zone in epilepsies with suspected insular involvement.