 Objective: To study the relative balance of GABA A binding potential and glutamate utilization in subjects with localization-related epilepsy with and without depression, subjects with major depressive disorder alone, and in subjects with generalized epilepsy expected not to have significant comorbid depression. Pilot data shows that GABAA binding potential and glutamate utilization are tightly coupled in healthy subjects, particularly in the mesial temporal lobe. We hypothesize that subjects with epilepsy will not exhibit the same degree of coupling, and that subjects with both epilepsy and depression will exhibit an even more pronounced decoupling. 