Focal brain lesions such as cortical dysplasia and glioneural tumors generate epileptic activity and thus may be synaptically connected with normal cortex. To test this hypothesis, we compared event-related potentials recorded directly from the medial temporal lobe (MTL) and a dysplastic lesion in eight patients with intractable temporal lobe epilepsy. The P3 component, related to visual target detection, showed different peak latencies in four patients and a larger intralesional amplitude compared to established anterior-MTL-generators in two patients. Semantic processing was identified by the N400 component and showed a different latency in four patients and larger intralesional amplitudes in two patients. These results are compatible with the hypothesis that cortical lesions interact with synaptic pathways related to cognitive functions such as visual target detection, and verbal processing.