Master of Science
For the 30-40% of persons with epilepsy (PWE) with refractory epilepsy, seizure freedom following surgery is affected by the localization of the epileptogenic zone (EZ). However, functional abnormalities can exist at a distance from the EZ, which may contribute to variable outcomes after surgery. Considering epilepsy as a network disorder (Pittau & Vulliemoz, 2015), and evaluating functional coupling among homotopic brain areas, may help predict cognitive outcomes. Homotopic areas are well connected anatomically and undoubtedly work synchronously to generate cognition. We evaluated 22 persons with focal epilepsy and 24 neurologically healthy controls using fMRI at rest and while watching a brief and engaging audiovisual film clip. The Glasser parcellation (Glasser et al., 2016), a surface-based atlas that divides each hemisphere into 180 cortical regions and 22 functionally distinct sections, was applied and a baseline distribution of homotopic connectivity between pairs of regions and sections was established based on a subset of controls. Regional distribution of homotopic coupling activity was investigated as well as the relationship with performance on neuropsychological measures. We demonstrate the combined utility of resting-state and movie-driven fMRI for detecting homotopic functional coupling abnormalities in persons with refractory temporal lobe epilepsy. In addition, we find evidence of patient-specific and widespread abnormal homotopic functional coupling in PWE within and outside the temporal lobe. Finally, we show that the relationship between homotopic coupling at rest and performance on neuropsychological assessments shows group differences. Our findings supplement evidence of altered functional connectivity in epilepsy using resting-state fMRI and demonstrate how the engaged brain is altered in focal epilepsy.
Summary for Lay Audience
42 Canadians are diagnosed with epilepsy everyday, and 1 in 3 persons with epilepsy (PWE) do not respond to seizure medication. Although surgical resection of the epileptogenic area is the treatment of choice for individuals with refractory epilepsy, the localization of epileptic activity can be difficult and consequently many individuals suffering from epilepsy have limited treatment options. This research aimed to improve pre-surgical assessment by using movie-driven and resting-state fMRI to identify alterations in homotopic functional coupling in PWE. Homotopic coupling is the functional connectivity between mirroring regions in the brain. Epilepsy is an incredibly diverse disease, and the outcomes of this study help to establish movie-driven fMRI as a technique that enables a patient-centered approach to pre-surgical assessment. We show that alterations in homotopic coupling in individuals with focal epilepsy are evident within and outside the temporal lobe. Furthermore, our results show that movie-driven and resting-state fMRI are differentially sensitive to the detection of homotopic coupling abnormalities in PWE. We find that this combined imaging approach will enhance sensitivity to subtle brain lesions, reduce the need for invasive EEG assessment, and improve the surgical options of individuals with ambiguous epileptic activity. The personal and economic burden of epilepsy is high, and surgery is less costly than ongoing medical care. Improving pre-surgical assessments and identifying connectivity alterations in PWE will enable the identification of brain regions and networks critical to the propagation of this disease and thus improve treatment options and patient outcomes.
Chadwick, Caroline M., "Homotopic Coupling in Persons with Epilepsy using Movie-driven and Resting-state fMRI" (2020). Electronic Thesis and Dissertation Repository. 7229.
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