HEMISPHERIC ASYMMETRY OF THE CALLOSAL INVOLVEMENT IN BILATERALLY SYNCHRONOUS EPILEPTIFORM DISCHARGES REVEALED BY DIRECT RECORDING OF CALLOSAL COMPOUND ACTION POTENTIALS
Abstract number :
1.144
Submission category :
Year :
2003
Submission ID :
3866
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Tomonori Ono, Hiroshi Baba, Keisuke Toda, Tohru Kamida, Kenji Ono Neurosurgery, National Nagasaki Medical Center, Omura, Nagasaki, Japan; Neurosurgery, Oita Medical University, Oita, Oita, Japan; Neurophysiology, Yokoo Hospital, Isahaya, Nagasaki, Japan
So far, while the callosal participation in some generalized epilepsies has long been supposed, selective activities of the callosal neurons have not been studied in relation to the epileptic seizures. Our recent study (Ono et al., Epilepsia 2002;43:1536-1542) of intraoperative electrocorticogram (ECoG) and callosal compound action potential (CCAP) revealed that the corpus callosum engages in the interhemispheric recruitment of bilateral epileptogenesis, i.e., callosal as well as other cortical neurons in the both hemispheres are simultaneously recruited, and thereby resulted in bilaterally synchronous spike and wave discharges (BSSWs). In this study, asymmetrical recruitment of the callosal neurons during BSSWs was evaluated and correlated with the EEG outcome after callosotomy.
In 16 patients undergoing corpus callosotomy for intractable epilepsy, intraoperative ECoGs and CCAPs were simultaneously recorded prior to the callosal section with the patients[apos] consent. CCAPs proper to each hemisphere during BSSWs (hemispheric CCAPs) were estimated through an averaging-based method. The degree of asymmetry in callosal involvement was defined as a laterality index (LI) based on the amplitude difference between hemispheric CCAPs. Postoperative EEG was visually assessed one month after the surgery.
Although preoperative BSSWs were common to all patients, the EEG outcome was categorized into either unilaterally lateralized epileptiform discharges (Group U, eight patients) or bilaterally asynchronous epileptiform discharges (Group B, eight patients). LI of Group U (0.51[plusmn] 0.1) was significantly higher than that of Group B (0.2 [plusmn] 0.04). In addition, higher amplitude of the hemispheric CCAP was coincident with the side of the postoperatively persisting seizure discharges in all of the Group U except one patient.
Our results suggested that the amount of recruited callosal neurons could be hemispherically asymmetric during bilateral synchrony, i.e., more callosal neurons are fired in the more epileptogenic hemisphere even if preoperative EEG features are virtually symmetric. This may support that the callosal system is not simply a route of epileptiform discharge but greatly influences on cortical epileptogenesis itself.