Introduction: Cortical brain areas are organized into networks that subsume both normal and pathological function. Mapping of these networks using correlated fluctuations of the blood oxygen level-dependent (BOLD) signal by functional connectivity analysis at rest (rfMRI) is a method used in the research arena to define brain networks involved in cognitive functions. However, the neurophysiological basis for these correlations remains unclear. Invasive electrode implantation for epilepsy surgery provides a means to probe these networks by cortical stimulation mapping in order to establish a neurophysiological basis and to define clinical utility.
Methods: 8 patients undergoing intracranial electrode implantations were used as subjects for this study. Preoperatively, patients underwent rfMRI scans. After electrode implantation, bipolar stimulation was performed at each electrode pair using single pulse electrical currents (10mA, 0.5Hz, 0.2 msec) and the cortico-cortical evoked response (CCEP) was measured at all other contacts. Electrodes were localized using post-operative CT and MRI. In addition, stimulation mapping was performed along clinical guidelines to define language and sensorimotor areas. Seeds were placed over the fMRI regions corresponding to stimulated electrodes to determine fMRI z-scores.
Results: fMRI z-score and CCEP amplitude revealed a significant (p<0.05) correlation within and across subjects. Functional sensorimotor and language as well as pathological seizure networks were demonstrated using this approach.
Conclusions: Our results show that networks defined by fMRI predict those defined by CCEP and have a neurophysiological basis. Furthermore, brain networks subsuming language and sensorimotor function as well as pathological networks involved in seizure spread can be mapped by these methods. Simirarly importantly this aids to reach higher accuracy in preoperative planning of tumor and epilepsy surgery near eloquent cortices with non-invasive techniques.
Patient Care: With more precise preoperative brain mapping modalities there will be less need for invasive mapping options, and the higher accuracy intraoperatively should reduce the possibility of a postoperative neurological deficit.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of non-invasive imaging, focusing on fMRI in tumor and epilepsy surgery close to eloquent cortices, 2) Discuss, in small groups the brain mapping options and the new application of resting state functional connectivity analysis , 3) Identify an effective combined preoperative diagnostic setting"