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Background: The stereoelectroencephalographic (SEEG) implantation procedures still represent a challenge due to the intrinsic complexity of the method and the number of depth electrodes required. Objectives: We aim at designing and evaluating the accuracy of a custom stereotactic fixture based on the StarFix™ technology (FHC Inc., Bowdoin, ME) that significantly simplifies and optimizes the implantation of depth electrodes used in presurgical evaluation of patients with drug-resistant epilepsy. Methods: Fiducial markers that also serve as anchors for the fixture are implanted into the patient's skull prior to surgery. A 3D fixture model is designed within the surgical planning software, with the planned trajectories incorporated in its design, aligned with the patient's anatomy. The stereotactic fixture is built using 3D laser sintering technology based on the computer-generated model. Bilateral rectangular grids of guide holes orthogonal to the midsagittal plane and centered on the midcommissural point are incorporated in the fixture design, allowing a wide selection of orthogonal trajectories. Up to two additional grids can be accommodated for targeting structures where oblique trajectories are required. The frame has no adjustable parts, this feature reducing the risk of inaccurate coordinate settings while simultaneously reducing procedure time significantly. Results: We have used the fixture for the implantation of depth electrodes for presurgical evaluation of 4 patients with drug-resistant focal epilepsy, with nearly 2-fold reduction in the duration of the implantation procedure. We have obtained a high accuracy with a submillimetric mean positioning error of 0.68 mm for the anchor bolts placed at the trajectory entry point and 1.64 mm at target. Conclusions: The custom stereotactic fixture design greatly simplifies the planning procedure and significantly reduces the time in the operating room, while maintaining a high accuracy.

Body awareness is the result of sensory integration in the posterior parietal cortex; however, other brain structures are part of this process. Our goal is to determine how the cingulate cortex is involved in the representation of our body. We retrospectively selected patients with drug‐resistant epilepsy, explored by stereo‐electroencephalography, that had the cingulate cortex sampled outside the epileptogenic zone. The clinical effects of high‐frequency electrical stimulation were reviewed and only those sites that elicited changes related to body perception were included. Connectivity of the cingulate cortex and other cortical structures was assessed using the h2 coefficient, following a nonlinear regression analysis of the broadband EEG signal. Poststimulation changes in connectivity were compared between two sets of stimulations eliciting or not eliciting symptoms related to body awareness (interest and control groups). We included 17 stimulations from 12 patients that reported different types of body perception changes such as sensation of being pushed toward right/left/up, one limb becoming heavier/lighter, illusory sensation of movement, sensation of pressure, sensation of floating or detachment of one hemi‐body. High‐frequency stimulation in the cingulate cortex (1 anterior, 15 middle, 1 posterior part) elicits body perception changes, associated with a decreased connectivity of the dominant posterior insula and increased coupling between other structures, located particularly in the nondominant hemisphere.

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