our findings are related to differences in social interactive style between the groups. The potential confound of marijuana use on social behavior should be investigated in future studies which include measures of personality and interactive behaviors. It is also unlikely that our results are due to acute marijuana intoxication. All study subjects reported being abstinent from marijuana use for a minimum of 12–16 hours prior to their scanning session, and fully expected that the investigators would be able to tell if they had used the drug since the previous evening upon their arrival at the lab, underscoring the likelihood that subjects were not intoxicated at the time of testing. Similarly, it is unlikely that the observed changes in the chronic marijuana smokers are the result of withdrawal effects from the drug. No subject endorsed any withdrawal symptoms at the time of testing, however, given the previous findings of withdrawal-related symptoms emerging between 24 and 48 hours after abstinence from marijuana (Haney et al., 1999; Kouri and Pope, 2000; Budney et al., 2001, 2002, 2004), this is not surprising, as subjects were seen well within a 24 hour period from their last use. Of course, despite subjects’ own report of no
