Irina Popa

Stimulation artifact correction method for estimation of early cortico-cortical evoked potentials

Highlights • New method for stimulation artifact removal from cortico-cortical evoked potentials.• The method is based on electrical modeling of tissue-electrode interface.• It allows disambiguation of time-locked physiological responses and artifacts.• Method validation is based on synthetic and experimental data.

Intrusive Thoughts Elicited by Direct Electrical Stimulation during Stereo-Electroencephalography

Cortical direct electrical stimulation (DES) is a method of brain mapping used during invasive presurgical evaluation of patients with intractable epilepsy. Intellectual auras like intrusive thoughts, also known as forced thinking (FT), have been reported during frontal seizures. However, there are few reports on FT obtained during DES in frontal cortex. We report three cases in which we obtained intrusive thoughts while stimulating the dorsolateral prefrontal cortex and the white matter in the prefrontal region. In order to highlight the effective connectivity that might explain this clinical response, we have analyzed cortico-cortical potentials evoked by single pulse electrical stimulation.

High frequency spectral changes induced by single-pulse electric stimulation: Comparison between physiologic and pathologic networks

OBJECTIVE To investigate functional coupling between brain networks using spectral changes induced by single-pulse electric stimulation (SPES). METHOD We analyzed 20 patients with focal epilepsy, implanted with depth electrodes. SPES was applied to each pair of adjacent contacts, and responses were recorded from all other contacts. The mean response amplitude value was quantified in three time-periods after stimulation (10-60, 60-255, 255-500ms) for three frequency-ranges (Gamma, Ripples, Fast-Ripples), and compared to baseline. A total of 30,755 responses were analyzed, taking into consideration three dichotomous pairs: stimulating in primary sensory areas (S1-V1) vs. outside them, to test the interaction in physiologic networks; stimulating in seizure onset zone (SOZ) vs. non-SOZ, to test pathologic interactions; recording in default mode network (DMN) vs. non-DMN. RESULTS Overall, we observed an early excitation (10-60ms) and a delayed inhibition (60-500ms). More specifically, in the delayed period, stimulation in S1-V1 produced a higher gamma-inhibition in the DMN, while stimulation in the SOZ induced a higher inhibition in the epilepsy-related higher frequencies (Ripples and Fast-Ripples). CONCLUSION Physiologic and pathologic interactions can be assessed using spectral changes induced by SPES. SIGNIFICANCE This is a promising method for connectivity studies in patients with drug-resistant focal epilepsy.

Successful epilepsy surgery in frontal lobe epilepsy with startle seizures: a SEEG study.

Pre-surgical assessment and surgical management of frontal epilepsy with normal MRI is often challenging. We present a case of a 33-year-old, right-handed, educated male. During childhood, his seizures presented with mandibular myoclonus and no particular trigger. As a young adult, he developed seizures with a startle component, triggered by unexpected noises. During his ictal episodes, he felt fear and grimaced with sudden head flexion and tonic axial posturing. Similar seizures also occurred without startle. Neuropsychological assessment showed executive dysfunction and verbal memory deficit. The cerebral MRI was normal. Electro-clinical reasoning, investigations performed, the results obtained and follow-up are discussed in detail. [Published with video sequence].

Connectomics in Patients with Temporal Lobe Epilepsy

The human brain is an amazingly complex structure whose functionality, including high-order cognitive functions, is determined by intricate connectivity patterns between tens of billions of neurons (Azevedo et al. 2009). The signaling between neurons is deceivingly simple, using binary-like electrical impulses, such that the multitude of brain functions, that are often performed concurrently, are the result of connectivity patterns across various spatial scales (Bullock et al. 1977; Budd and Kisvarday 2012), that implement a mixed sequential, parallel or hierarchical architecture. The brain regulates breathing and heart rate, collects and processes sensory information, and controls all the voluntary and involuntary movements and actions. While some of these functions are performed by well-defined areas of the brain (i.e. visual stimuli are processed solely by the primary visual cortex), some higher level functions (i.e. speech production, problem solving, music performance) can only be accomplished by various brain areas working together in a serial or, more likely, in a parallel or distributed design (Sigman and Dehaene 2008).

P241 Insula connectivity during wakefulness and sleep studied through single pulse electrical stimulation during seeg recordings

Objective We aim to study the connections of the posterior insula (pI) and anterior insula (aI) through cortico-cortical evoked potentials (CCEP) by single pulse electrical stimulation (SPES). Method We performed SPES stimulation protocol in a group of 8 refractory epilepsy patients presurgically explored with intracerebral depth electrodes, out of which 6 were operated on and are currently seizure-free. We selected the early responses (ER) obtained from contacts of 24 electrodes that were included in the anterior and posterior insula, when this structure was outside the seizure onset zone (SOZ). Responses were analyzed in terms of amplitude variations during wakefulness and sleep. Effective connectivity betweeen cortical was calculated based on the measured CCEPs. Results The ER amplitudes by SPES stimulation in the insula during wakefulness compared to sleep showed statistically significant ( p 0.05 ) differences in 6 patients. There are constant connections between aI and pI. We identified connectivity of the pI with language-related brain stuctures during wakefulness, and with the temporal mesial structures during sleep, possibly influenced by the SOZ. Right pI stimulation seems to elicit ampler reponses in the rolandic operculum and parietal structures during wakefulness, and in the primary motor and premotor cortex during sleep. Anterior insula has preferential connectivity with anterior cingulate gyrus during wakefulness and with the fusiform gyrus during sleep. Discussions Connectivity of the aI versus pI, as well as right versus left insula during wakefulness and sleep is different, partially supporting previous observations. Conclusion Sleep has been shown to alter the physiological connectivity of the insula. Further investigations are in progress to confirm these results. Significance These findings describe insular connectivity and variability during sleep, with possible implications in epilepsy surgery, sleep disorders understanding and language studies.