Past or current medical condition that would interfere with brain function- 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; sensitivity to flashing lights. Subjects requiring regular medication.