The study lasts for 8 weeks and involves 5 total visits to the clinic. Throughout the study, all subjects will receive either escitalopram (Lexapro) or citalopram (Celexa) on the basis of the study doctor's clinical judgment. The dose of the medications can be increased at any point in time if the study doctor thinks it is appropriate. After the first screen visit (which lasts about 3 hours), each subsequent half-hour visit will involve a 2-tablespoon blood draw to measure BDNF levels, as well as a QEEG in which small, painless electrodes are stuck to the subject's forehead and electrical activity of the brain is measured. At the end of the 8 weeks, subjects are offered 3 months of free follow-up care, including medications.