Role of corpus callosum in interhemispheric coherent activity during sleep

Objective To investigate to what extent the increase in interhemispheric coherent activity observed from wakefulness to sleep depends on the integrity of the corpus callosum (CC). Methods Interhemispheric coherent activity was analyzed in two epileptic patients selected for callosotomy because of multifocal refractory epilepsy, before and 4 months after callosotomy. One patient underwent complete callosotomy and another was subjected to callosotomy of the anterior 2/3, which offered the possibility of comparing the role of the CC in the coherent activity increase from wakefulness to sleep, between anterior regions with interrupted CC communication (in the two patients) and posterior regions with intact communication (in one of them). Results were compared with a group of normal subjects. Results Both patients showed increased coherent activity from wakefulness to sleep after surgery. Conclusions Results demonstrate that interhemispheric coherent activity, despite an attenuation after surgery, is higher during SWS than during wakefulness after sectioning the CC; however, they have to be taken with caution because they come from two patients only. Significance Present results show that the increase in coherent activity during sleep does not depend exclusively on callosal integrity but also on state-dependent influences from sleep-promoting mechanisms, probably spread throughout the thalamo–cortical network.