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Accentuated cortico-cortical evoked potentials in neocortical epilepsy in areas of ictal onset Volume 12, numéro 4, December 2010

Figure 1 Illustration of the CCEPs in patient 1 (top row). The volume-rendered brain MRI of the right fronto-temporal region is displayed from the anterior inferior oblique view. One six-contact subdural strip electrode is placed over the right anterior basal temporal cortex towards the entorhinal cortex. One 2x6 subdural grid electrode is placed on the anterior lateral temporal cortex towards the temporo-polar region. CCEPs were recorded from circled electrodes. Anatomical relationship is depicted next to the MRI. One form of ictal EEG initiated at the electrode over the entorhinal cortex and spread to the anterior lateral temporal region (bottom row). CCEPs after stimulation of the ictal onset zone and after stimulation outside the ictal onset zone are compared. Stimulus intensity was 9 mA for both. Size of the full circles is proportional to the amplitude of N1 peak for the given stimulation. In this way, a distribution of the response is shown for the given stimulation and they cannot be used for comparison between stimulations (such as between iCCEP or nCCEPs data sets). 100% amplitude is assigned to the electrode with the largest N1 response. The angle of pie (painted in black) shows the relative latency of N1, i.e. latency delay from the earliest N1.

Figure 2 Illustration of the CCEPs in patient 2. Sagittal section of the patient's MRI shows one 2 x 6 grid placed in the right mesial fronto-parietal cortex and another 2 x 6 grid placed anteriorly over the mesial frontal and superior frontal gyrus. CCEPs were recorded from 14 of these electrodes, as shown in the image. The stimulation at the ictal onset zone produced larger N1 responses. The stimulus intensity versus N1 amplitude curve from the iCCEP showed greater increment than that from the nCCEP.

Figure 3 Results for patients 3, 4 and 5. CCEPs were recorded from the right orbito-frontal cortex (patient 3), left lateral temporal cortex p 4), and left perirolandic cortex (patient 5). The latencies and CCEP waveforms are shown on the right with the iCCEP (A) and the nCCEP (B). The stimulation at the ictal onset zone evoked larger N1 in patients 3 and 4. In patient 5, the stimulation outside the ictal onset zone produced larger responses. The grey-painted area in patient 5 shows the area of cortical atrophy.