Provocation frequency and its role in determining the effects of smoked marijuana on human aggressive responding

Five male subjects participated in an experiment to determine how variations in provocation frequency, manipulated before and after smoking marijuana, would affect free-operant aggressive responding. Two response buttons, A and B, were available. Pressing button A was maintained by a fixed-ratio 100 schedule of point presentation. Subjects were instructed that the completion of each fixed-ratio 10 on button B resulted in a point subtraction from a second subject (who was in fact fictitious). Button B responses were defined as aggressive, since they ostensibly resulted in the presentation of an aversive stimulus (i.e., point subtraction) to another person. Aggressive responding was engendered by a random-time schedule of point subtraction and maintained by the initiation of intervals free from point subtraction. Points subtracted from the subjects were attributed to the fictitious other subject. The effects of smoking placebo and 3.58% w/w Delta-9-tetrahydro-canabinol marijuana cigarettes, on aggressive responding under four different provocation conditions, were studied: (1) low provocation before and low provocation after smoking; (2) low provocation before and high provocation after smoking; (3) high provocation before and low provocation after smoking; and (4) high provocation before and after smoking. Manipulating the level of provocation frequency immediately before smoking marijuana had no effect on the number of aggressive responses emitted after smoking marijuana. Rather, the provocation frequency immediately after smoking marijuana was important. After smoking active marijuana cigarettes, aggressive responding was significantly suppressed, relative to placebo, under the high provocation condition but not under the low provocation condition. As a result, the effects of marijuana on aggression appear to be largely determined by the environmental conditions (i.e., level of provocation frequency and/or rate of aggressive responding) present immediately after smoking marijuana. This finding may help to account for some of the inconsistencies observed in previous studies, where marijuana has been found to both increase and decrease aggressive responding.