No history of alcoholism, psychiatric or neurological illness, head trauma with loss of consciousness, history of exposure to central nervous system toxin; history of central nervous system infection, metabolic, endocrine, connective tissue disease; hypertension or other cardiovascular disorder; abnormal renal, liver or pulmonary function; blood or coagulation disease; malignancy; psychopharmacological treatment; neurodegenerative or neurodevelopmental disorder; stroke; epilepsy; subjects requiring regular medication, and subjects demonstrated by drug screening to have taken a controlled substance.