Lamotrigine Therapy in Geriatric Bipolar Depression

Inclusion Criteria (for Bipolar Subjects): * 60 years or older * Meet DSM-IV diagnostic criteria for Bipolar Disorder, Current Episode Depressed * First episode of mania before the age of 50 (early-onset bipolar disorder) * Montgomery-Asberg Depression Rating Scale (MADRS) Score of greater or equal to 20. * Young Mania Rating Scale (YMRS) of less than or equal to 6. * Able to provide informed consent * Must speak English * Must be able to visit McLean Hospital for the screening visit and six study visits during the 8-week duration of the study. * Subjects may be taking other medications for bipolar depression including antidepressants, mood stabilizers and antipsychotic mediations prior to lamotrigine therapy, but may not have any dosage adjustments of these medications in the week before lamotrigine is added. Exclusion Criteria (for Bipolar Subjects): * Serious or unstable medical illness, including cardiovascular, hepatic, renal, respiratory, endocrine, neurologic or hematologic disease. * History of seizure disorder * History or current diagnosis of the following psychiatric illnesses: any organic mental disorder (including dementia), schizophrenia, schizoaffective disorder, delusional disorder, psychotic disorder not otherwise specified, unipolar major depressive disorder, patients with substance dependence disorders, including alcohol, active within the last 12 months. * First episode of mania after the age of 50 (to exclude late-onset bipolar disorder) * History of multiple adverse drug reactions or allergy to the study drugs. * Use of medications that are excluded in this study (benzodiazepines, barbiturates; however, the use of non-benzodiazepine sedative hypnotics (such as zolpidem (Ambien)) may be used as needed except within 48 hours of the MRI scan) * Any of the exclusion criteria mentioned in the MRI risks section below Inclusion Criteria (for Controls): * 60 years or older * Able to provide informed consent * Must speak English * Women entering this study must be post-menopausal Exclusion Criteria (for Controls): \- Same criteria for the Bipolar Depressed group with the exception of the "first episode of mania" which is not applicable.