Patient description: The patient is a 55-year-old man who was recently diagnosed with Parkinson's disease. He is complaining of slowness of movement and tremors. His disease is ranked as mild, Hoehn-Yahr Stage I. His past medical history is significant for hypertension and hypercholesterolemia. He lives with his wife. They have three children. He used to be active with gardening before his diagnosis. He complains of shaking and slow movement. He had difficulty entering through a door, as he was frozen and needed guidance to step in. His handwriting is getting smaller. He is offered Levodopa and Trihexyphenidyl. He is an alert and cooperative man who does not have any signs of dementia. He does not smoke or use any illicit drugs.

Clinical trial eligibility criteria: eligible ages (years): 18.0-64.0,  HIV Dementia Men and women 18 years of age or older and less than 65 years of age. Able to read and understand English. HIV infected on stable ART regimen for 5 months or greater, and not likely to change regimen for the duration of the study. Significant dementia but able to give consent (International HIV Dementia Scale score <10). Significant cognitive slowing on screening, defined as 1 SD below normal (t-score >60) on the Conner's CPT-II reaction time test. Beck Depression Inventory score <16. Documented HIV-1 RNA PCR <50 copies/mL and documented CD4 count >200 within 3 months of entry visit. Baseline CBC and chemistry panel Grade 1 or normal. For females of reproductive potential (women who have not been post-menopausal for at least 24 consecutive months, i.e., who have had menses within 24 months prior to study entry), or women who have not undergone surgical sterilization, specifically hysterectomy or bilateral oophorectomy or tubal ligation) will require a negative serum or urine pregnancy test within 48 hours prior to entry. NOTE: Subject reported history is considered acceptable documentation of hysterectomy, bilateral oophorectomy, tubal ligation, tubal micro-inserts, menopause, and vasectomy/azoospermia. All subjects must agree not to participate in the conception process (e.g., active attempt to become pregnant or to impregnate, sperm donation, in vitro fertilization), and if participating in sexual activity that could lead to pregnancy, the subject/partner must use at least two reliable methods of contraception, (condoms, without a spermicidal agent; a diaphragm or cervical cap without spermicide; an IUD; or hormone-based contraceptive), for 2 weeks before study treatment, while receiving study treatment, and for 6 weeks after receiving study treatment. Ability and willingness of subject to provide informed consent  Inability to give informed consent. No proxy consent allowed. Uncontrolled hypertension (SBP >140 and DBP >90 at screening and baseline). Untreated hypogonadism, hypothyroidism or hyperthyroidism. Initiation of antidepressants, thyroid medication or anabolic steroids within 6 weeks of screening visit. Pregnancy or breast feeding. Clinically significant EKG abnormalities at screening. History of coronary artery disease, atherosclerotic disease, left ventricular hypertrophy, cardiomegaly, syncope, congestive heart failure, myocardial infarction, pacemaker, clinically significant arrhythmia, angina, history of treatment for arrhythmia. Brain related opportunistic infections, stroke, intracranial lesions/disease, or meningitis. History of epilepsy. Untreated depression. Uncontrolled diabetes (glucose <70 or >200 at screening). Use of interferon or ribavirin during study and for 1 month prior to screening. History of bipolar disorder, Alzheimer's dementia, ALS, Parkinson's disease or other medical dementias other than HIV-related. History of schizophrenia, mania or other serious mental illness. History of methylphenidate allergy. Other serious concurrent medical illness other than HIV. History of radiation therapy to the brain or brain injury. History of crystal methamphetamine, cocaine, LSD use or other recreational substance use other than marijuana within the 12 months prior to screening and for the duration of the study. Plan to use marijuana or marinol during the entire study duration and one month prior to screening visit. Plan to drink 7 or more alcoholic drinks per week during the 4 weeks prior to screen visit and for the duration of the study. History of alcohol dependence, alcohol abuse, cocaine addiction, crystal methamphetamine addiction or other recreational drug addiction or treatment for addiction or dependence within 5 years of screening visit. If subject is using prescription narcotics, should be on a stable dose for at least 1 month prior to screening and throughout the study. Previous use of Concerta™, Ritalin™, atomexitine or Adderall™ or other psychostimulants (e.g. modafinil, armodafinil) for 3 months prior to screening visit and for duration of the study. History of tic disorders in the past 3 months or any history of Tourette's syndrome. Greater than 10% below ideal body weight (IBW for men = 50 kg + 2.3 kg per inch over 5 feet of height, and IBW for women = 45.5 kg + 2.3 kg per inch over 5 feet of height) Uncontrolled migraine headaches. History of short gut syndrome, Meckel's diverticulum, or cystic fibrosis. Family history of sudden cardiac death in a young relative. History of fainting with exercise. History of attention deficit disorder will be excluded, defined as a score greater than 6 on the Childhood ADHD Symptoms Scale. -