Evaluation of connectivity measures to identify Seizure Onset and Propagation Zones in Refractory Epilepsy: A Case study with two different Post- Surgical Outcomes.

High Frequency Oscillations (HFO) have been found very useful in refractory epilepsy. They have been used to identify the epileptogenic zone and as a promising clinical biomarker for presurgical evaluation in childhood epilepsy. There is controversy about whether there is a spread of HFOs and their propagation. Some researchers reinforce the idea of dealing with epilepsy as a network disorder, so the fact of propagation can promote this research. The hypothesis of this study is that connectivity methods can be useful to detect the seizure onset and propagation zones. Methodology has been applied to two cases where the clinical outcomes after surgery were free of seizures and not free. Promising results were obtained to understand both situations. A future study with more cases is necessary to obtain strong conclusions.Clinical Relevance- This exploratory study shows the relationship between connectivity measures and the propagation of HFOs and this can be useful to know the epileptogenic function of these waves that, nowadays, are unknown. Connectivity features in conjunction with other multivariate estimators can be a tool to help in identifying the regions of interest in refractory epilepsy.

Cortical inhibition on TMS-EEG: interstimulus interval effect on short-interval paired-pulse.

In mental disorders, paired-pulse (PP) transcranial magnetic stimulation and electroencephalography (TMS-EEG) recordings usage is increasing to directly evaluate the cortical inhibition of motor and nonmotor regions. One of the most common measures to assess the inhibition is the short-interval cortical inhibition (SICI), which depends on the interstimulus interval (ISI). This measure has been widely used in the motor cortex. However, the number of studies that evaluate other nonmotor regions, such as the dorsolateral prefrontal cortex (DLPFC), are increasing and there is still little knowledge on how the ISI affects those areas.In this pilot study, six subjects underwent a SICI protocol over the DLPFC using ISI values of 2 and 4ms with the aim of comparing them. TMS-EEG signals for both ISIs were characterized regarding the amplitude and latency of the TMS-evoked potentials (TEP) P60 and N100. Whereas the variation of cortical inhibition between ISIs is almost significant for N100, with higher inhibition for an ISI of 2ms, for TEP P60 the variation was not appreciable. Findings are in accordance with the ones in the state-of-the-art obtained in the motor cortex and suggest that a greater inhibition is likely to be produced with an ISI of 2ms.Clinical relevance- This pilot study indicates that cortical inhibition might be better assessed when DLPFC is stimulated with an ISI of 2ms in the SICI protocol.

Cognitive stimulation has potential for brain activation in individuals with Rett syndrome.

BACKGROUND: Knowledge regarding neuropsychological training in Rett syndrome (RS) is scarce. The aim of this study was to assess the outcome and the duration of the effect of cognitive stimulation on topographic electroencephalography (EEG) data in RS. METHODS: Twenty female children diagnosed with RS were included in the analysis. Girls with RS conducted a cognitive task using an eye-tracker designed to evaluate access and choice skills. EEG data were acquired during the experimental procedure including two 10-min baseline stages before and after the task. Topographical changes of several EEG spectral markers including absolute and relative powers, Brain Symmetry Index and entropy were assessed. RESULTS: Topographic significance probability maps suggested statistical decreases on delta activity and increases on beta rhythm associated with the cognitive task. Entropy increased during and after the task, likely related to more complex brain activity. A significant positive interaction was obtained between Brain Symmetry Index and age showing that the improvement of interhemispheric symmetry was higher in younger girls (5-10 years). CONCLUSIONS: According to our findings, significant alterations of brain rhythms were observed during and after cognitive stimulation, suggesting that cognitive stimulation may have effects on brain activity beyond the stimulation period. Finally, our promising results also showed an increase brain symmetry that was especially relevant for the younger group. This could suggest an interaction of the eye-tracking cognitive task; however, further studies in this field are needed to assess the relation between brain asymmetries and age.

Novel measure of the weigh distribution balance on the brain network: graph complexity applied to schizophrenia.

The aim of this study was to assess brain complexity dynamics in schizophrenia (SCH) patients during an auditory oddball task. For this task, we applied a novel graph measure based on the balance of the node weights distribution. Previous studies applied complexity parameters that were strongly dependent on network topology. This could bias the results, as well as making correction techniques, such as surrogating process, necessary. In the present study, we applied a novel graph complexity measure derived from the information theory: Shannon Graph Complexity (SGC). Complexity patterns from electroencephalographic recordings of 20 healthy controls and 20 SCH patients during an auditory oddball task were analyzed. Results showed a significantly more pronounced decrease of SGC for controls than for SCH patients during the cognitive task. These findings suggest an important change in the brain configuration towards a more balanced network, mainly in the connections related to long-range interactions. Since these changes are significantly more pronounced in controls, a deficit in the neural network reorganization can be associated with SCH. In addition, an accuracy of 72.5% was obtained using a receiver operating characteristic curve with a leave-one-out cross-validation procedure. The independence of network topology has been demonstrated by the novel complexity measure proposed in this study, therefore, it complements traditional graph measures as a means to characterize brain networks.

Analysis of the non-stationarity of neural activity during an auditory oddball task in schizophrenia.

The aim of this study was to characterize brain dynamics during an auditory oddball task. For this purpose, a measure of the non-stationarity of a given time-frequency representation (TFR) was applied to electroencephalographic (EEG) signals. EEG activity was acquired from 20 schizophrenic (SCH) patients and 20 healthy controls while they underwent a three-stimulus auditory oddball task. The Degree of Stationarity (DS), a measure of the non-stationarity of the TFR, was computed using the continuous wavelet transform. DS was calculated for both the baseline [-300 0] ms and active task [150 550] ms windows of a P300 auditory oddball task. Results showed a statistically significant increase (p<;0.05) in non-stationarity for controls during the cognitive task in the central region, while less widespread statistically significant differences were obtained for SCH patients, especially in the beta-2 and gamma bands. Our findings support the relevance of DS as a means to study cerebral processing in SCH. Furthermore, the lack of statistically significant changes in DS for SCH patients suggests an abnormal reorganization of neural dynamics during an oddball task.