Coupling of cortical and thalamic metabolism in experimentally induced visual and somatosensory focal epilepsy

Focal epileptic activity induces widespread metabolic disturbances beyond the area of the electroencephalographically detectable focus. In order to find out whether the metabolic coupling between the epileptic focus and other brain regions depends on the localization of the focus, two groups of rats with epileptic foci at different sites were investigated. In the first group acute epileptic activity was induced by application of penicillin to the secondary visual cortex (Oc2), and in the second group to the primary somatosensory cortex (Par1). Metabolism was analyzed using the [14C]deoxyglucose autoradiographic method. In both groups of animals, hypermetabolism in the area of the focus and in specific functionally coupled thalamic nuclei was observed. Focal epileptic activity in the secondary visual cortex induced significant hypometabolism in remote ipsilateral cortical areas. In rats with epileptic foci in the primary somatosensory cortex hypometabolism in extrafocal ipsilateral cortical areas was less prominent. These findings provide further support for the integral involvement of the thalamus in modulating metabolism in remote cortical brain regions during focal epileptic activity. The extent of metabolic alterations may depend on the site of the epileptic focus and the connectivity of the recruited thalamic nuclei.