Introduction: The cerebral cortex is composed of functional modules that are distinct from pathological modules that are targets for resection in epilepsy surgery. Current invasive electrode protocols are limited by sampling the entirety of these modules. We applied resting functional MRI (fMRI) to parcel brain areas based upon intrinsic functional connectivity (iFC). We used iFC gradients (Wig et al., 2014) to distinguish functionally distinct cortical areas within brains of individual patients (Xu et al., 2016) undergoing epilepsy surgery. We then tested these gradient-based parcellations against clinical identifications of functional and seizure onset zones obtained from invasive monitoring.

Methods: For 3 patients with focal neocortical epilepsy, gradients were derived from iFC similarity and used to define edges for a functional parcellation of brain areas within each subject (Xu et al., 2016). These parcellations were compared directly to functional and epileptogenic brain areas identified in the course of invasive mapping. Areas of function were defined using data from clinical stimulation mapping (CSM) of implanted patient electrodes. For this analysis, assessment of brain function was restricted to language (including speech arrest, picture naming, auditory naming) and motor phenomena. Areas involved in seizure onset were identified using epileptologist review of intracranial electroencephalography.

Results: Gradient-based resting fMRI parcellations corresponded to either a functional or an epileptogenic zone of the brain identified in the course of invasive surgical monitoring for each of the 3 patients studied. In one patient, gradient-based parcellations correspond to edges of the seizure onset zone as defined by invasive monitoring (Figure 1). We find that gradient-based resting fMRI parcellations can identify regions of function and epileptogenic pathology in the brain in this limited sample.

Conclusions: Gradient-based resting fMRI parcellation provides a promising method to identify seizure onset zones as well as functional zones in the brain.

Patient Care: Improve the outcome of epilepsy surgery Improve preservation of function after brain surgery

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Understand the application of resting fMRI to create intraindividual parcellation of the neocortex. 2) Apply this understanding to epilepsy surgery

References: Wig GS, Laumann TO and Petersen SE. 2014. An approach for parcellating human cortical areas using resting state correlations. Neuroimage. 93:276-291. Xu T, Opitz A, Craddock RC, Zuo XN and Milham M. 2016. Assessing variations in areal organizaSon for the intrinsic brain: From fingerprints to reliability. Cerebral Cortex. 26:4192-4211.