EXCLUSION CRITERIA: (1) current or past DSM-IV Axis I disorder other than substance abuse/dependence (2) any significant non-psychiatric medical illness requiring ongoing medical treatment (3) any clinically significant abnormality on EKG (4) hypertension (5) cardiovascular disease (6) substance dependence other than cocaine, marijuana, or nicotine within the last 3 months. (7) Positive breath alcohol (8) Positive urine drug screen for drugs other than cocaine or THC at the time of behavioral testing (9) For female subjects: known pregnancy or a positive pregnancy test or current breast feeding (10) Diagnosis of Adult Attention Deficit Disorder as determined by: a) meeting DSM-IV criteria for childhood ADHD, b) currently has impairing ADHD symptoms, c) ADHD symptoms can not have remitted at any period since childhood (11) HIV positive (12) I.Q. below 70 (13) Use of medications which affect the central nervous system (CNS) or could interact with SYN115. (13) History of pacemaker or metal implants or welding or metal work without protective eyewear.