IntrAnat Electrodes: A Free Database and Visualization Software for Intracranial Electroencephalographic Data Processed for Case and Group Studies

In some cases of pharmaco-resistant and focal epilepsies, intracranial recordings performed epidurally (electrocorticography, ECoG) and/or in depth (stereoelectroencephalography, SEEG) can be required to locate the seizure onset zone and the eloquent cortex before surgical resection. In SEEG, each electrode contact records brain’s electrical activity in a spherical volume of 3 mm diameter approximately. The spatial coverage is around 1% of the brain and differs between patients because the implantation of electrodes is tailored for each case. Group studies thus need a large number of patients to reach a large spatial sampling, which can be achieved more easily using a multicentric approach such as implemented in our F-TRACT project (f-tract.eu). To facilitate group studies, we developed a software—IntrAnat Electrodes—that allows to perform virtual electrode implantation in patients’ neuroanatomy and to overlay results of epileptic and functional mapping, as well as resection masks from the surgery. IntrAnat Electrodes is based on a patient database providing multiple search criteria to highlight various group features. For each patient, the anatomical processing is based on a series of software publicly available. Imaging modalities (Positron Emission Tomography (PET), anatomical MRI pre-implantation, post-implantation and post-resection, functional MRI, diffusion MRI, Computed Tomography (CT) with electrodes) are coregistered. The 3D T1 pre-implantation MRI gray/white matter is segmented and spatially normalized to obtain a series of cortical parcels using different neuroanatomical atlases. On post-implantation images, the user can position 3D models of electrodes defined by their geometry. Each electrode contact is then labeled according to its position in the anatomical atlases, to the class of tissue (gray or white matter, cerebro-spinal fluid) and to its presence inside or outside the resection mask. Users can add more functionally informed labels on contact, such as clinical responses after electrical stimulation, cortico-cortical evoked potentials, gamma band activity during cognitive tasks or epileptogenicity. IntrAnat Electrodes software thus provides a means to visualize multimodal data. The contact labels allow to search for patients in the database according to multiple criteria representing almost all available data, which is to our knowledge unique in current SEEG software. IntrAnat Electrodes will be available in the forthcoming release of BrainVisa software and tutorials can be found on the F-TRACT webpage

The Effect of low frequency oscillation phase on memory encoding

Oscillatory activity is a ubiquitous property of brain signals. The importance of the phase of EEG for processing naturalistic stimuli, which have typically long duration, is still not clear. In this study, we presented word-nonword pairs, each of which was visible for five seconds and measured the effect of EEG phase during stimulus onset on later memory recall. The task consisted of an encoding phase in which 20 word-nonword pairs were presented, followed by a testing phase in which subjects where shown one of the seen words with four target nonwords to choose from. We found that memory recall performance was higher when the words during encoding were presented at a descending phase of the theta oscillation. This effect was the strongest over the frontal cortex. These results suggest that the phase of ongoing cortical activity can affect memorization of persistent stimuli which are an integral part of daily tasks

An Intracranial Electroencephalography (iEEG) Brain Function Mapping Tool with an Application to Epilepsy Surgery Evaluation

Object: Before epilepsy surgeries, intracranial electroencephalography (iEEG) is often employed in function mapping and epileptogenic foci localization. Although the implanted electrodes provide crucial information for epileptogenic zone resection, a convenient clinical tool for electrode position registration and brain function mapping visualization is still lacking. In this study, we developed a Brain Function Mapping (BFM) Tool, which facilitates electrode position registration and brain function mapping visualization, with an application to epilepsy surgeries.Methods: The BFM Tool mainly utilizes electrode location registration and function mapping based on pre-defined brain models from other software. In addition, the electrode node and mapping properties, such as the node size/color, edge color / thickness, mapping method, can be adjusted easily using the setting panel. Moreover, users may manually import / export location and connectivity data to generate figures for further application. The role of this software is demonstrated by a clinical study of language area localization.Results: The BFM Tool helps clinical doctors and researchers visualize implanted electrodes and brain functions in an easy, quick and flexible manner.Conclusions: Our tool provides convenient electrode registration, easy brain function visualization, and has good performance. It is clinical-oriented and is easy to deploy and use. The BFM tool is suitable for epilepsy and other clinical iEEG applications

Effects of sensory information over the motor and somatosensory cortex activity during standing

The purpose of this study was to identify changes in cortical hemodynamics of motor and somatosensory cortex related to balancing tasks during inhibition of muscle spindles and cutaneous receptors of the dominant leg. Data were obtained from twelve participants (age: 24.8 +/- 4.59 years). The study consisted of four randomized order visits to identify cortical hemodynamic changes while standing under normal conditions (Ctrl), with muscle spindles inhibited (MSI), with cutaneous receptors inhibited (CB), and with the muscle spindles and cutaneous receptors inhibited (BOTH). Muscle spindles were inhibited by applying five minutes of vibration over the soleus muscle; pre- and post-vibration (MSI and BOTH) H-reflex amplitude was measured for later statistical analysis. Lidocaine was applied and left over the foot sole for 30 minutes; sensitivity threshold and two-point discrimination variables were obtained under normal conditions (Ctrl) and anesthetic effect (CB and BOTH). Cortical hemodynamics were measured using an fNIRS placed over each participant's head while performing two counterbalanced blocks of bipedal and unipedal standing with the eyes closed. During MSI and BOTH five minutes of vibration were applied before each block of standing tasks. Statistical analysis consisted of performing different repeated measures ANOVA; then, if needed, post-hoc test consisted of several paired samples t-test (corrected for multiple comparisons). Findings revealed that, compared to pre-, H-reflex amplitude was significantly lower after vibration. Lidocaine findings were inconclusive with a higher sensitivity threshold on the heel during BOTH than Ctrl, but two-point discrimination did not show any significant effect among the visits. Body sway was not different among visits but increased from bipedal to unipedal standing. Cortical hemodynamics revealed that mean oxyhemoglobin activity was not different during bipedal standing among the visits, but it was different during visits that inhibited muscle spindles compared to visits that did not inhibit muscle spindles. In conclusion, muscle spindle inhibition of the soleus muscle can alter the motor and somatosensory cortex's cortical hemodynamics during unipedal standing, but these changes did not influence balance performance. Cutaneous block might not be achieved by applying lidocaine over the foot sole for 30 minutes; therefore, conclusions regarding the cutaneous receptors' influence were not possible

Pseudo-online Detection and Classification for Upper-limb Movements from Scalp Electroencephalogram

Stroke has been a significant healthcare issue worldwide, leading to motor impairment and complicated rehabilitation procedures, which often last for years after lesion. In recent years, brain-computer interface (BCI) research shed some light on new approaches for motor ability recovery and potential neural plasticity inducement for stroke patients. Electroencephalogram (EEG) is widely used in BCI to measure brain activity. In this thesis study, nine healthy participants were recruited to perform four movements in a self-initiated manner, including left wrist extension (WE_L), right wrist extension (WE_R), left index finger extension (IE_L), and right index finger extension (IE_R). A hierarchical structure was proposed first to detect movement intentions from the rest state and then classify different movement types. Movement-related cortical potential (MRCP) and sensorimotor rhythm (SMR) were believed to associate with movement intention generation in human EEG. Thus, three frequency bands of EEG (0.05-5Hz, 5-40Hz, 0.05-40Hz) containing MRCP or SMR were investigated to provide features for detection and classification algorithms. In detection, a majority voting-based ensemble learning method was proposed to integrate the strongness of three algorithms, including support vector machine (SVM), EEGNET, and Riemannian feature-based SVM. The proposed method achieved an average true positive rate (TPR) of 79.6% ± 8.8%, false positives per minute (FPs/min) as 3.1 ± 1.2 within a latency of 91.4 ± 111.9ms. For classification, an adaptive boosting-based ensemble learning algorithm was proposed to classify movement pairs and four movements in pseudo-online and time-locked analyses. As a result, It proved the feasibility of classifying movements in different arms with higher than significant chance level accuracy. In summary, the proposed system offered a novel solution to decode upper-limb movements for rehabilitation-aimed BCI