Effect of callosal bisection on seizure development and interhemispheric transfer effects in feline motor cortical...

Motor cortical (MC) kindling was carried out in 12 adult cats, seven with the corpus callosum (CC) intact and five with the CC bisected, to study interhemispheric transfer effects and the effect of callosal bisection on both seizure development and interhemispheric transfer effects. MC kindling developed from partial motor seizures to partial onset generalized convulsions. Interhemispheric negative transfer effect, but not positive, existed in secondary site kindling and primary site retest of the CC-intact group, as shown by: (i) electroencephalographically lateralized seizure development in the stimulated hemisphere; (ii) delayed generalization of partial onset generalized convulsions; and (iii) a markedly unstable generalized convulsive seizure state. The CC-bisected group showed: (i) significantly delayed seizure development from partial motor seizure stage to generalized convulsive seizure stage in primary and secondary kindling; (ii) facilitated intrahemispheric seizure development; (iii) the diminution of interhemispheric negative transfer effect; (iv) modified generalized convulsions showing extremely asymmetrical generalized convulsions shifting from contralaterally dominant convulsions to ipsilaterally dominant ones (n = 2) or alternate generalized convulsions changing from contralateral hemiconvulsions to ipsilateral ones (n = 3). The results obtained suggest that the CC plays a major role in interhemispheric seizure propagation as well as interhemispheric negative transfer effects in MC kindling and may have suppressive effect on intrahemispheric motor seizure development in MC kindling. However, interhemispheric seizure propagation and interhemispheric negative transfer effects were mediated via other structures, possibly subcortical structures, when the CC was bisected.