Summary:Purpose: By means of the intraoperative electrophysiologic observation, we reevaluated the "transfer" theory that a transcallosal volley invoked by a cortical spike discharge in one hemisphere directly causes its contralateral counterpart via the corpus callosum (CC).Methods: Twenty-six patients who underwent corpus callosotomy were the subjects of this study. Intraoperatively, electrocorticograms from both hemispheres were simultaneously monitored with callosal compound action potentials (CCAPs) from the CC. Analysis was conducted on (a) the interhemispheric delay of bilaterally synchronous spike-and-wave discharges (BSSWs), and (b) the chronological relation between BSSWs and CCAPs.Results: The side of prior spike discharges was never fixed but was occasionally reversed. Interhemispheric delays between the BSSWs were not constant, regardless of direction, and fluctuated in all patients. Most of the interhemispheric delays were distributed within 20 ms with a mode of 0 ms. The waveform of the CCAP was characterized by slow-rising negative potential change that attained its peak after a cortical spike discharge. These findings were identical in all the patients regardless of whether the BSSWs were changed or unchanged after callosotomy.Conclusions: If the "transfer" role of the CC is true, interhemispheric delays between BSSWs must be longer than interhemispheric axonal conduction time (about 20 ms), and a preceding cortical spike discharge must produce a CCAP and then a contralateral one in order of time. However, this hypothesis was not confirmed in the present study. We propose the interhemispheric recruitment of the epileptogenic state as a different role of the CC on epileptogenesis.

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Summary:  Purpose: To define the most appropriate time for surgery for medically intractable epilepsies in infants and young children. Methods: First we examined retrospectively the changes in developmental quotients (DQs) during the clinical course and the clinical factors affecting the DQ in 39 consecutive patients younger than 15 years, who underwent surgical treatment for intractable epilepsy. Second, we examined prospectively five new patients for early detection of developmental arrest or regression by periodic developmental assessments and whether this could lead to early surgical intervention, eventually resulting in minimal developmental defects. Results: Retrospective studies revealed that the DQ progressively decreased with age and that the reduction of DQ was related to continuing frequent seizures in many patients. The prospective studies demonstrated that periodic developmental assessments could detect the reduction of DQ at 5 months or later after onset of frequent seizures in three patients. In two other patients, operations were performed before reduction of DQs, and their postoperative DQ levels were normal. The postoperative recovery of DQ was complete in one patient whose operation was performed 3 months after reduction of DQ, whereas it was incomplete in two others whose operations were carried out at 12 and 14 months after reduction, respectively. Furthermore, three patients with normal developmental outcome had shorter periods between the onset of frequent seizures and the operation (≤7 months) than those of two patients with developmental delay (≥17 months). Conclusions: To minimize the developmental defects, periodic developmental assessments should be initiated when frequent seizures have occurred, and surgery should be considered as soon as possible when DQ reduction is recognized.

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