Adolescents often differ notably from younger or older individuals in the ways they respond to and interact with meaningful stimuli in their environment. Such adolescent-typical characteristics include marked elevations in interactions with peers, novelty seeking/risk taking, and consummatory behaviors (Spear, 2000, 2007a). Interactions with peers become particularly important during adolescence, with these interactions beginning to exert a greater influence over decision-making and behavior than they do among adults (Gardner & Steinberg, 2005; Grosbras et al., 2007; Steinberg, 2005). During adolescence, humans spend more time interacting with peers than at any other developmental period (Hartup & Stevens, 1997), and these relationships provide a significant source of positive experiences for adolescents (Brown, 2004; LaGreca et al., 2001, Steinberg & Morris, 2001). Similarly, during the age interval from postnatal days (P) 28 to 42, which has been conservatively defined as adolescence in the rat (for review see Spear, 2000), rats demonstrate higher levels of social activity than younger and older animals. These high levels of social interactions are particularly characterized by play fighting in adolescence, in contrast to social investigation which predominates the
