- subjects who are diagnosed as suffering from psychotic illness according to DSM-IV (Axis 1) (American Psychiatric Association, 1994) or with a history of CNS disease, a history of infection that might affect CNS (HIV, syphilis, cytomegalovirus, herpes), a history of head injury with loss of consciousness, history of other substance abuse taking psychoactive medications (shown by urine test). Abnormal liver test results (150% above average) will be excluded. Pregnancy is also an exclusion criterion, as radiation exposure is risky for the fetus.