Abstract
Introduction: EEG-fMRI detects BOLD changes associated with epileptic interictal discharges (IED) and can identify epileptogenic networks in epilepsy patients. Besides positive BOLD changes, negative BOLD changes have sometimes been observed in the default-mode network, particularly using group analysis. A new fast fMRI sequence called MREG (Magnetic Resonance Encephalography) shows increased sensitivity to detect IED-related BOLD changes compared to the conventional EPI sequence, including frequent occurrence of negative BOLD responses in the DMN. The present study quantifies the concordance between the DMN and negative BOLD related to IEDs of temporal and extra-temporal origin.Methods: Focal epilepsy patients underwent simultaneous EEG-MREG. Areas of overlap were calculated between DMN regions, defined as precuneus, posterior cingulate, bilateral inferior parietal and mesial prefrontal cortices according to a standardized atlas, and significant negative BOLD changes revealed by an event-related analysis based on the timings of IED seen on EEG. Correlation between IED number/lobe of origin and the overlap were calculated.Results: 15 patients were analyzed, some showing IED over more than one location resulting in 30 different IED types. The average overlap between negative BOLD and DMN was significantly larger in temporal (23.7 ± 19.6 cm3) than extra-temporal IEDs (7.4 ± 5.1 cm3, p = 0.008). There was no significant correlation between the number of IEDs and the overlap between DMN structures and negative BOLD areas.Discussion: MREG results in an increased sensitivity to detect negative BOLD responses related to focal IED in single patients, with responses often occurring in DMN regions. In patients with high overlap with the DMN, this suggests that epileptic IEDs may be associated with a brief decrease in attention and cognitive ability. Interestingly this observation was not dependent on the frequency of IED but more common in IED of temporal origin.
Highlights
EEG-functional magnetic resonance imaging (fMRI) detects Blood Oxygenation Level Dependent (BOLD) changes associated with epileptic interictal discharges (IED) and can identify epileptogenic networks in epilepsy patients
Areas of overlap were calculated between default mode network (DMN) regions, defined as precuneus, posterior cingulate, bilateral inferior parietal and mesial prefrontal cortices according to a standardized atlas, and significant negative BOLD changes revealed by an event-related analysis based on the timings of IED seen on EEG
There was no significant correlation between the number of IEDs and the overlap between DMN structures and negative BOLD areas
Summary
EEG-fMRI detects BOLD changes associated with epileptic interictal discharges (IED) and can identify epileptogenic networks in epilepsy patients. Zijlmans and colleagues showed that EEG-fMRI can be a useful additional diagnostic tool in the presurgical evaluation of patients with refractory epilepsy by improving the identification of patients suitable for surgery (Zijlmans et al, 2007). This observation was confirmed by a study providing evidence that the surgical removal of the area with the strongest positive BOLD is correlated with a good postsurgical seizure outcome (Thornton et al, 2010; An et al, 2013). There is strong evidence that BOLD changes related to epileptic spikes are able to identify epileptic networks www.frontiersin.org
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