Objectives: The objectives of this study are to test the hypotheses that direct infusion of the brain (convection enhanced delivery) with neurotransmitter receptor agonists is 1) safe and 2) can be used to study the basic pathophysiology of the epileptic focus in human subjects. The approach described may be a new approach for precise localization of a seizure focus. It may also prove to indicate the distribution of suppression (in space) required for elimination of seizure activity in individual patients and, by doing so, may more accurately define the minimum treatment area that is required for success. Finally, the data obtained may support the treatment of patients with medically intractable epilepsy with neurotransmitter-specific agents infused directly into the epileptic focus.