Abstracts

Rationale: Patients with drug resistant epilepsy may undergo invasive evaluation with SEEG electrodes to assess epileptic network activity. Determining the correct location and extent of resection is critical to achieving seizure freedom. Cortico-cortical evoked potentials (CCEPs) provide a means to examine functional connectivity in near and distant regions of the brain. Responses to stimulation recorded in and around areas which were subsequently resected leading to freedom from seizures can provide valuable insight into the epileptic network.


Methods: A group of 11 subjects were studied, each of which were rendered seizure free by a right temporal lobectomy following an evaluation which included pre- and post-operative MRI’s, and invasive evaluation with SEEG electrodes which included CCEPs stimulation. The MRI’s were used to ascertain which SEEG contacts were located in cortex which was subsequently resected. The “in degree” of CCEPs responses (those recorded on a single contact when other pairs of contacts were stimulated) were collated for comparison.


Results: The CCEPs recorded from each subject were averaged for each stimulation pair and converted to a root mean square voltage (V_RMS). All subjects had a temporal lobectomy with resection of mesial structures. Contacts within the ipsilateral limbic network were classified with respect to the subsequently performed resection. The largest inward connectivity was seen in the temporal pole, followed by the hippocampus. A summary is shown in the attached figure. An analysis of outliers was performed, considering the largest 10% of responses per subject per region, which also showed larger average responses in the resected regions.


Conclusions: Resected regions appear to have greater inward effective connectivity, reflecting that the nodes have a greater propensity to be primary activators (receiver nodes) within the epileptogenic network.


Funding: -