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Adolescent-Typical Behavior Patterns 21As discussed previously, adolescents of a variety of mammalian species differconsiderably from younger juveniles and older adults in the ways they seekout and interact with stimuli in their environment, including notable elevationsin peer-directed social interactions and novelty seeking/risk taking behaviors(see Spear, 2000, for review) and the reward value they attribute to those stimuli(e.g., Douglas et al., 2003, 2004). It is also during adolescence that drug andalcohol use is typically initiated, with use of alcohol becoming normative amonghuman adolescents (e.g., Shedler & Block, 1990). Adolescents of other speciessuch as the rat likewise often drink notably more alcohol than their mature counterparts(e.g., Brunell & Spear, 2005; Doremus et al., 2005), presumably in partdue to their insensitivity to aversive ethanol effects that serve as cues to limitintake (see Spear & Varlinskaya, 2005, for review and references), an insensitivityseemingly related in part to immaturity in GABAergic systems (Silveri &Spear, 2002). Conversely, early adolescents are more sensitive than their moremature peers to several alcohol consequences, including ethanol-induced socialfacilitation (Varlinskaya & Spear, 2002) and impairments in brain plasticity andmemory (Acheson et al., 1998; Swartzwelder et al., 1995a), with the latter enhancedsensitivity related in part to overexpression of hippocampal glutaminergicsystems early in adolescence (Swartzwelder et al., 1995b). Studies in laboratoryanimals and using fMRI techniques in humans are just beginning to relatespecific components of the neural circuitry undergoing change during adolescenceto expression of typical behaviors of adolescents as well as their cognitive/emotional maturation.When contemplating the relationship between cognitive/behavioral function ofadolescence and the sculpting of adolescent brain, it may be important to considerthe complicating variable of stress. The PFC and certain other mesocorticolimbicbrain regions undergoing transformation during adolescence are highlysensitive to stressors (e.g., Dunn, 1988), and there is some evidence that adolescencemay be a particularly stressful stage, with reports that adolescents not onlyare exposed to more life stressors (e.g., Buchanan et al., 1992), but also responddifferently to stressors than at other ages (see Spear, 2000, for review). Adolescentsoften appear particularly sensitive to stressors, a phenomenon that can bemodeled in laboratory animals, with rodents at this age showing more stressinducedbehavioral disruption (e.g., Stone & Quartermain, 1998; Walker et al.,1995) and different patterns of stress-induced neural activation (Choi & Kellogg,1996) than adults.Normal developmental alterations in brain occurring during adolescence mayinfluence expression of psychopathology in vulnerable individuals. Along withwell-known examples of adolescent-associated emergence of overt symptomatologysuch as schizophrenia are examples where considerable reductionsin symptomatology are often observed during adolescence (e.g., Tourette’ssyndrome: Kurlan, 1992; childhood epilepsy: Saugstad, 1994). In research with