Temporal lobe seizure interhemispheric propagation time depends on nonepileptic cortical cerebral blood flow

In some patients with epilepsy, activation of eloquent cortex using various forms of environmental stimulation and mental activity may induce seizures. The increased neuronal activity resulting from cortical stimulation may be associated with increased regional cerebral blood flow. The vascular steal theory of temporal lobe epilepsy suggests that as nonepileptogenic cortical cerebral blood flow (CBFn) increases, temporal lobe epileptogenicity increases as a result, in part, of decreasing interhemispheric propagation time (IHPT). Recently, IHPT has been shown to be a quantitative electrocorticographic measure of temporal lobe epileptogenicity. In the current study, long-term combined subdural-EEG and surface cortical cerebral blood flow (CBF) monitoring was performed to test the hypothesis that IHPT depends upon CBFn. The results show that IHPT is a nonlinear (negative exponential) function of nonepileptic cortical CBF (r=0.507, df=32, t=-2.204, P<0.05). In temporal lobe epilepsy, nonepileptic cortical hypoperfusion may represent a protective mechanism for delaying interhemispheric seizure propagation. The fact that IHPT decreases exponentially with increasing CBFn suggests that small increases in CBFn should substantially decrease IHPT and increase epileptogenicity. This study confirms that inter-hemispheric propagation time depends upon perfusion of nonepileptogenic cortex.