P06-S Temporal lobe connectivity changes during wakefulness and sleep studied through single pulse electrical stimulation

Abstracts / Clinical Neurophysiology 130 (2019) e21–e116

at risk and the underlying mechanisms for accelerated cognitive decline are vital for guiding interventions and improving early prediction of dementia. We propose a novel approach for risk prediction using repeated electrophysiological recording prior to and following visuospatial cognitive stimulation. Methods: Forty-six consensus diagnosed, non-demented, community dwelling African American older participants over age 60 years received EEG and NIH Toolbox-Cognition and Brief CogState computer administered cognitive batteries. In between two resting EEG (eyes closed) sessions participants engaged in a visual motion direction discrimination task for approximately 20 min. The outcome measures were % changes of spectral power between pre/post EEGs. Results: There was a decrease in spectral power of eyes-closed EEG across all the frequency ranges at post as compared pre-EEG recording, with the greatest at the beta range (12–30 Hz) – 41% (p < .0005), followed by delta (1–4 Hz) – 4% (p < .0005), theta (4–8 Hz) – 3% (p < .0005), while there was no significant difference at alpha range (8–12 Hz) – <1%. The % decrease of beta power was also significantly correlated with performance on the Toolbox Total Composite, Crystalized Intelligence, and Oral Picture recognition. Conclusions: Our preliminary results demonstrate that EEG reactivity, repeated eyes-closed baseline EEG after short visual cognitive stimulation, showed significant decrease primarily in beta range that correlated with neuropsychological performance. Thus, the baseline EEG reactivity findings are very promising in terms of identifying those older adults who are at risk for accelerated cognitive decline. doi:10.1016/j.clinph.2019.04.543

P04-S Dose-dependent synchronization of ongoing alpha oscillation by repetitive transcranial magnetic stimulation—Elina Zmeykina *, Zsolt Turi, Walter Paulus (Georg-August-University Göttingen, Göttingen, Germany) ⇑

Corresponding author.

Repetitive transcranial magnetic stimulation (rTMS) is shown to modulate ongoing neural activity by means of inducing an oscillating electric field (E-field) in the cortical regions. Traditionally, rTMS induces an intracranial peak E-field in the range of 90–110 V/m. However, in vitro experiments show that a 1–5 V/m E-field is enough to entrain ongoing rhyth. Therefore, we hypothesized that inducing E-fields magnitudes less than 50 V/m is enough to entrain ongoing parietal alpha oscillations. We tested the hypothesis by enrolling sixteen healthy participants in a single-blind, repeated measure study. First, we estimated the magnitudes of E-fields by using MR-derived realistic head models. Participants were stimulated with three intensities corresponding to 20 (LOW), 35 (MED) and 50 (HIGH) V/m E-fields. The bursts of 20 TMS pulses were applied at individual alpha frequency. The effect was controlled by arrhythmic stimulation that consisted of twenty pulses at random intra-burst frequencies. rTMS induced effect was studied during and after rTMS by electrophysiological changes of parietal alpha. We found that phase synchronization of an ongoing activity with external pulses was increased during rhythmic rTMS but not for arrhythmic rTThe amount of synchronization expressed in phase locking values was progressively larger for increasing intensity in a dose-dependent manner. After effects of rTMS were present for LOW and HIGH stimulation intensities. Rhythmic rTMS increased while arrhythmic rTMS decreased the power of parietal alpha. Overall, our study demonstrated that rTMS at intensities about two times lower than those traditionally

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used could successfully modulate the parietal alpha rhythm in resting state. doi:10.1016/j.clinph.2019.04.544

P05-S Brain networks activated while performing high-frequency intracranial stimulation for functional cortical mapping—Andrei Barborica a,*, Ioana Mindruta b, Cristian Donos a, Irina Popa b, Felicia Mihai a, Mihai Maliia a, Andrei Daneasa b, Anca Arbune b, Constantin Pistol a (a Physics Department, Bucharest University, b Bucharest-Magurele, Romania, Neurology Department, Bucharest University Emergency Hospital, Bucharest, Romania) ⇑

Corresponding author.

Background: High-frequency intracranial stimulation is an essential method for mapping brain function. It is considered that clinical effects result primarily from tissue activation near the stimulation site. However, it may be possible that certain symptoms emerge from activating broader networks, that we aim at uncovering using advanced stimulation and EEG signal analysis. Materials and methods: Uncovering EEG responses to intracranial high-frequency electrical stimulation is difficult due to the presence of stimulation artifacts. By using alternating stimulation polarity, a method originally used for resolving the electrically evoked compound action potentials in auditory nerve fibers, we show that it is possible to recover the electrophysiological responses during intracranial stimulation and identify brain functional networks. In 17 patients undergoing presurgical evaluation for drugresistant epilepsy, we have applied stimulation and recorded responses on 64–128 depth electrode contacts. The activation of the networks at stimulation levels evoking a clinical symptom was compared with the activation below threshold, that did not elicit any clinical effects, allowing to evidence a selective recruitment of pathways associated with a particular symptom. Results: A number of 706 out of 1966 sites elicited symptoms while stimulated, at a mean intensity of 1.27 mA. We were able to identify functional brain networks involved in various somatosensory (143 symptoms), motor (154), visual (55), language-related symptoms (41) and ictal symptoms (78), among others. Conclusions: The alternating polarity stimulation protocol proved effective in resolving the activations associated with clinical effects. doi:10.1016/j.clinph.2019.04.545

P06-S Temporal lobe connectivity changes during wakefulness and sleep studied through single pulse electrical stimulation— Anca Adriana Arbune a,b,*, Ioana Mindruta a,b, Andrei Daneasa b, Mihai Maliia b, Irina Popa a,b, Jean Ciurea c, Cristian Donos d, Ovidiu Alexandru Bajenaru a,b, Andrei Barborica d (a ‘‘Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania, b University Emergency Hospital Bucharest, Bucharest, Romania, c ‘‘Bagdasar-Arseni” Emergency Hospital, Bucharest, Romania, d University of Bucharest, Department of Electricity and Magnetism, Solid-State Physics, and Biophysics, Bucharest, Romania) ⇑

Corresponding author.

Background: Temporal lobe epilepsy is frequently improved after selective resection. However, a small number of these patients have

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Abstracts / Clinical Neurophysiology 130 (2019) e21–e116

temporal-plus epilepsy and continue seizing. We aim to study the connectivity of the temporal lobe during wakefulness and sleep. Material and methods: We included 25 patients with drugresistant focal epilepsy who had depth electrodes exploration in 2016–2018. We implanted 9–18 electrodes per patient over a large network. We performed single pulse electrical stimulation protocol, as previously described, during wakefulness and sleep. We selected 40,678 statistically significant responses (rho > 0.4, p < 0.05) and we analyzed only temporal structures. Results: The difference between the mean responses in all temporal structures between sleep and wakefulness is 10.41 lV (p < 0.01). When part of the epileptogenic zone (EZ), the difference becomes 8.02 lV (p < 0.05). Stimulation of the right temporal EZ produced higher responses during sleep in the left hemisphere and right occipital lobe, while left temporal EZ elicited significantly higher responses in the left parietal (p < 0.05). The highest connectivity increase was in the left fusiform gyrus - hippocampus connection (p < 0.01). When outside the EZ, all temporal structures exhibit a decrease in connectivity during sleep with the left frontal (p < 0.05). Stimulation of the nonepileptogenic left temporal structures elicits higher responses during sleep in the right temporal (p < 0.01). The highest increase was of the left frusiform gyrus-TPO junction connectivity (p < 0.01). Conclusions: Temporal lobe connectivity is modulated by sleep, EZ location, and pertainence of certain structures to the EZ, with statistically significant differences between left and right temporal structures. doi:10.1016/j.clinph.2019.04.546

ISI 200 ms and facilitation at ISI 100 At a group level, paired pulse TMS differentiated between healthy controls, patients with epilepsy and patients without epilepsy. To establish the true potential, data of more patients is needed, which may enable analysis at the individual level. doi:10.1016/j.clinph.2019.04.547

P08-S Combined electromagnetic source imaging in presurgical evaluation—Lene Duez a,*, Hatice Tankisi a, Peter Orm Hansen a, Anne Sabers b, Lars Pinborg b, Martin Fabricius c, György Rásonyi c, Guido Rubboli d, Birthe Pedersen d, Anne-Mette Leffers e, Peter Uldall f, Bo Jespersen g, DMSc Jannick Brennum g, Otto Mølby Henriksen h, Anders Fuglsang-Frederiksen a, Sándor Beniczky a,b (a Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark, b Department of Neurology, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark, c Department of Clinical Neurophysiology. Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark, d Danish Epilepsy Centre, Dianalund, Denmark , e Department of Diagnostic Radiology, Hvidovre Hospital, Hvidovre, Denmark, f Department of Pediatrics, child neurology.Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark, g Department of Neurosurgery, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark, h Department of Clinical Physiology, Nuclear Medicine and PET, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark) ⇑

P07-S Multimodal TMS has the potential to improve the diagnostic process in epilepsy—Annika de Goede a,*, Michel van Putten a,b (a Clinical Neurophysiology, University of Twente, Enschede, Netherlands, b Department of Clinical Neurophysiology and Neurology, Medisch Spectrum Twente, Netherlands) ⇑

Corresponding author.

Background: In epilepsy, a disturbed cortical excitability results in a predisposition to generate seizures. The limited diagnostic sensitivity of the electroencephalogram motivates the search for a novel biomarker. Transcranial magnetic stimulation (TMS) is a technique to assess cortical excitability. We used a multimodal TMS approach to evaluate differences between healthy controls, first seizure patients diagnosed with epilepsy and those without epilepsy. Methods: We included twenty-one healthy subjects and twentyone first seizure patients, of which seven were diagnosed with epilepsy. Both motor cortices were stimulated with 50 single pulses and 50 paired pulses at six interstimulus intervals (ISIs) between 50–300 As single pulse TMS readouts we analyzed amplitudes of the motor evoked potential (MEP) and TMS evoked potential (TEP). For paired pulse stimulation, we assessed long intracortical inhibition (LICI) of the MEP and TEP. Results: We found no significant differences in MEP or TEP amplitudes using single pulse TCompared to healthy controls, epilepsy patients showed significantly increased LICI of the N100 and P180 components for ISI 200 Furthermore, we found facilitation at ISI 100 ms in epilepsy patients and inhibition in patients without epilepsy. Conclusions: Multimodal TMS has the potential to improve the diagnostic process in epilepsy. Biomarkers include increased LICI at

Corresponding author.

Background: To date, source imaging (SI) has been performed using epileptiform discharges (ED) detected by magnetoencephalography (MEG) or electroencephalography (EEG). A few case studies has combined MEG and EEG recordings and performed electromagnetic source imaging (cEMSI). This study tries to elucidate the role of cEMSI in presurgical evaluation. Material and methods: A MEG whole-head 306-channel Elekta NeuromagÒ system, and simultaneous high density EEG (70 electrodes, range 58–80) using a non-magnetic cap (EASYCAP) were recorded in 141 consecutive patients. Fifty patients were operated and had one year follow up. MEG-EEG was inspected for EDs. Signals were analyzed using CURRY 7 Neuroimaging Suite. For each cluster, using the visually detected EDs as templates, automated algorithms scanned the recordings, and detected EDs were visually checked. To improve the signal-to-noise ratio, EDs with similar topography were averaged. Two different inverse solutions were applied: equivalent current dipole (ECD) and a distributed source model (DSM): sLORETA. We performed electric SI, magnetic SI, and cEMSI. All analyses were performed using individual head models from the patients’ MRIs. We calculated the odds ratio (OR) of becoming seizure-free when operation was concordant vs discordant with the localization of the SI. Results: Combining both EEG and MEG signals (cEMSI) gave an OR of 5.8 for ECD and 19.2 for DSM. OR of cEMSI using DSM was significantly higher than both ESI (p = 0.02) and MSI (p = 0.03). Conclusion: Combined EMSI achieved significantly higher odds ratio for becoming seizure-free compared to electric SI and magnetic SI. doi:10.1016/j.clinph.2019.04.548