Abstracts

Rationale: Previous EEG-fMRI and EEG-fNIRS studies suggest that focal spikes show remote hemodynamic effects, such as activations/deactivationsa. Very little is however known about the remote electromagnetic activity at the time of epileptic spikes. The goal of this study was to investigate oscillatory activity in brain regions far away from the epileptic focus at the time of the spikes as compared to spike-free activity. Methods: We selected 44 consecutive patients scanned in Magnetoencephalography at the Montreal Neurological Institute for presurgical evaluation, who showed at least 10 frontal or anterior temporal spikes. We excluded patients with spike-and-wave complex and large brain regions. MEG data was reconstructed on the individual high-resolution MRIb. The epileptic focus was localized using the Coherent-Maximum Entropy on the Mean Methodb to confirm that the spike generator was in the anterior regions. The dynamic of the oscillatory activity was investigated bilaterally in three regions of interest (ROIs) of the posterior quadrant: inferioparietal, precuneus, calcarine cortices. After projecting MEG data on the cortical surface with the Minimum Norm Estimation, Morlet time-frequency decomposition was run from 1 to 80Hz in a 2 seconds time-window around the spikes and on a similar number of spike-free epochs for all ROIs. Parametric statistics and false discovery rate correction for multiple comparisons were applied to test differences between subjects’ average time-frequency maps of spike-related versus spike-free activity. Results: As compared to spike-free epochs, spike-epochs showed: a) higher 1 to 7 Hz activity from -1 to +1 seconds; b) 1 to 40Hz activity increase from -200 to +200 ms; c) 12-15 Hz increase after the spike, up to 1s after the spike (t>4, p c, the 1 to 40 Hz increase may be related to the direct effect of the spikes on remote regions and the 12-15Hz post-spike increase may correspond to inhibitory activity triggered by the spikes. Conclusions: We showed that focal spikes are strongly and consistently associated to transient oscillatory activity in remote regions of the brain. Such effects can be unveiled in the time-frequency domain using magnetoencephalography and may reflect both the direct effect of the spikes on remote activity and the inhibitory response that they trigger.References:a. Pellegrino G et al., Hemodynamic Response to Interictal Epileptiform Discharges Addressed by Personalized EEG-fNIRS Recordings. Front Neurosci. 2016 Mar 22;10:102.b. Pellegrino G et al., Source localization of the seizure onset zone from ictal EEG/MEG data. Hum Brain Mapp. 2016 Jul;37(7):2528-46c. Pellegrino G et al., Slow Activity in Focal Epilepsy During Sleep and Wakefulness. Clin EEG Neurosci. 2017 May;48(3):200-208. Funding: CIHR (MOP-93614), NSERC, FRQS, CECR, and American Epilepsy Society Early Career Physician-Scientist award. GP has beenfunded by Richard and Edith Strauss Canada Foundation and from an operating grant of the Italian Ministry of Health to the IRCCS Fondazione San Camillo Hospital.