Different structures involved during ictal and interictal epileptic activity in malformations of cortical development: an EEG-fMRI study

Abstract

Malformations of cortical development (MCDs) are commonly complicated by intractable focal epilepsy. Epileptogenesis in these disorders is not well understood and may depend on the type of MCD. The cellular mechanisms involved in interictal and ictal events are notably different, and could be influenced independently by the type of pathology. We evaluated the relationship between interictal and ictal zones in eight patients with different types of MCD in order to better understand the generation of these activities: four had nodular heterotopia, two focal cortical dysplasia and two subcortical band heterotopia (double-cortex). We used the non-invasive EEG-fMRI technique to record simultaneously all cerebral structures with a high spatio-temporal resolution. We recorded interictal and ictal events during the same session. Ictal events were either electrical only or clinical with minimal motion. BOLD changes were found in the focal cortical dysplasia during interictal and ictal epileptiform events in the two patients with this disorder. Heterotopic and normal cortices were involved in BOLD changes during interictal and ictal events in the two patients with double cortex, but the maximum BOLD response was in the heterotopic band in both patients. Only two of the four patients with nodular heterotopia showed involvement of a nodule during interictal activity. During seizures, although BOLD changes affected the lesion in two patients, the maximum was always in the overlying cortex and never in the heterotopia. For two patients intracranial recordings were available and confirm our findings. The dysplastic cortex and the heterotopic cortex of band heterotopia were involved in interictal and seizure processes. Even if the nodular gray matter heterotopia may have the cellular substrate to produce interictal events, the often abnormal overlying cortex is more likely to be involved during the seizures. The non-invasive BOLD study of interictal and ictal events in MCD patients may help to understand the role of the lesion in epileptogenesis and also determine the potential surgical target.

Independent component analysis reveals dynamic ictal BOLD responses in EEG-fMRI data from focal epilepsy patients

“…Ictal events lacking significant clinical symptoms, particularly movements, are particularly wellsuited for recording in the MRI scanner, as motion may result in highly contaminated fMRI data . Compared to other studies in the literature (Di Bonaventura et al, 2006a;Kobayashi et al, 2006;Salek-Haddadi et al, 2002;Tyvaert et al, 2008), the 15 patients in the current study constitute a sizable number, but ictal events are still quite infrequently recorded during EEG-fMRI sessions. However, it should be noted that none of the patients had originally been recruited on the basis of their seizure frequency.…”

“…The GLM results from patient #1 were presented previously in Kobayashi et al (2006) and patients #2-4 and #6-9 were presented in Tyvaert et al (2008). A description of the results for all patients is presented in Table 2.…”

“…They did not necessarily include clinical symptoms, and thus were not exactly equivalent to the patients' usual seizures. Nevertheless, the regions identified from these events may provide an important indication of the epileptogenic zone, which cannot be determined from interictal events alone (Tyvaert et al, 2008). Subclinical electrographic seizures usually originate from the same location as clinical seizures (Sperling and O'Connor, 1990).…”

“…Recently, some EEG-fMRI studies have investigated the BOLD response to ictal discharges in patients with focal epilepsy (Di Bonaventura et al, 2006a;Kobayashi et al, 2006;SalekHaddadi et al, 2002;Tyvaert et al, 2008). Due to the unpredictability of ictal events, patients are generally selected for an interictal investigation, with the occurrence of ictal events left to chance, although it is possible to target patients with frequent seizures (Di Bonaventura et al, 2006b;Federico et al, 2005b).…”

Brain state regulation during normal development: Intrinsic activity fluctuations in simultaneous EEG–fMRI

“…Evidence for human thalamocortical activity during rest has been obtained noninvasively by simultaneous recording of EEG and fMRI. These studies revealed that activity in the alpha range ( 10 Hz) is accompanied by BOLD activity in a thalamocortical network (TCN) with thalamus positively correlated and sensory areas negatively correlated (de Munck et al, 2007;Difrancesco et al, 2008;Feige et al, 2005;Goldman et al, 2002;Lüchinger et al, 2011;Moosmann et al, 2003;Tyvaert et al, 2008). Such functional coupling is typically based on temporal correlation of frequency-specific EEG power fluctuations (convolved with the slow hemodynamic response function) with the co-registered regional BOLD signal in eyes-closed resting state.…”