This 24-week treatment study will evaluate each patient’s response to treatment using neuropsychological testing and state-of-the-art brain imaging. The brain tests include neuropsychological testing of memory and attention, brain imaging (MRI and PET scans) to look at blood flow in the brain and nerve cell structure and metabolism, a neurological exam, and studies of the fluid that surrounds the brain (cerebrospinal fluid). The treatment involves 10 weeks of either intravenous antibiotic called ceftriaxone (also known as Rocephin) or intravenous placebo (inactive substance). After the first visit to Columbia Presbyterian Medical Center, the remaining treatments will be done in the patient’s home. Patients will be screened over the phone and in person to confirm study eligibility.