ABSTRACT

The leading theory on the origin of absence seizures, the cortico-reticular theory, supposes that a subcortical pacemaker is responsible for normal sleep spindles and pathological spike-wave discharges (SWDs). It postulates that the thalamic relay cells in the basolateral complex of the thalamus, the reticular thalamic nucleus and the cortex, aşembled in a thalamo-cortico-thalamic network, generate both types of EEG oscillations. Recently, Meeren et al. (2002) proposed a focal theory of absence epilepsy. This theory, based on experimental findings in the WAG/Rij rats supposes that the somatosensory cortex contains a focus that initiates a cascade of events that lead to the occurrence of bilateral and generalized SWDs. In this review, new data are presented which show that the cortex of WAG/Rij rats contains areas including the somatosensory cortex, which lack parvalbumin. Second, local deactivation of the focal zone with lidocaine reduces the inci - dence of SWDs. Finally, branching of dendrites of neurons is abnormal in this zone. All these new results p r ovide further support for the focal theory of absence epileps y. The question as to whether similar or comparable pathophysiological proceşes are present in humans needs to be elucidated. The new focal theory can be easily tested in humans with respect to the location of the origin of the EEG oscillations.