Thirty-one healthy volunteers (15 males, 16 females)
aged 18-57 years (29.6 ± 10.7 years) were enrolled from the Charles Village and
Roland Park communities in Baltimore, Maryland, USA. Written consent for each
volunteer was obtained, and the study was approved by the institutional review boards of Johns Hopkins
University and the John Hopkins Medical Institutions. All the subjects were free
from any history of neurological disorder or psychiatric disease. Out of these 31
subjects, 19 were Caucasian, 8 were Asian, 2 were African American and 2 were
Hispanic. Subject ages (males 28.3 ± 9.9 years; females 30.9 ± 11.5 years) and
the education level were not significantly different between the two groups (p
= 0.47 and p = 0.46 respectively).