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Substance Abuse and Addiction 393defects evident during adolescence at a time when the brain is developing arereversible after long-term abstinence. There is evidence that substantial recoveryof short-term but not long-term memory can occur in adults (Brandt, Butters, Ryan,& Bayog, 1983). Individuals who experienced heavy alcohol exposure duringadolescence could have more or less recovery than adults depending on the longtermeffects of alcohol on the developing brain, but appropriate longitudinal studieshave not yet been done (Brown & Tapert, 2004).Animal experiments tend to support the implications of the correlational studiesin clinical populations. Early exposure to alcohol involves exposing the developingbrain to a neurotoxin that could produce effects beyond simply abuse ordependence in the future (Brown & Tapert, 2004). There is abundant evidencefrom animal models that shows changes in response to alcohol during development.Spear (2004) points out that rodent models of adolescence show a combinationof reduced sensitivity to cues that would tend to moderate alcohol intake,such as motor impairment and sedation, but increased sensitivity to other effects,such as social facilitation. One of the major structures affected by alcohol is thehippocampus (White & Swartzwelder, 2004), which plays a key role in learningand memory. Adolescent rats are more sensitive to the effects of alcohol on NMDAreceptor-mediated synaptic potentials (Swartzwelder, Wilson, & Tayyeb, 1995a).Long-term potentiation (LTP), which is believed to be part of the underlyingmechanism of memory, is more affected by alcohol in adolescent than in adultrats (Swartzwelder, Wilson, & Tayyeb, 1995b).MarijuanaMarijuana is the most commonly used illegal drug. Its use peaked in 1979 amonghigh school students and has fluctuated over the years in inverse proportion to theperception of harm (figure 17-2). As perception of risk goes up, experimentationwith marijuana goes down. There is controversy over the dangers of marijuana.Clearly it has a direct effect on attention, learning, and memory. Thus it would beexpected to diminish school performance if taken during class or homework time.This concept is supported by studies showing a correlation between marijuana useand poor school performance (Bergen, Martin, Roeger, & Allison, 2005). But suchfindings may not imply a causal relationship.There is good evidence that cognitive impairment persists beyond the periodof the marijuana “high,” but it is unclear whether these residual effects last longerthan a day or two (Pope & Yurgelun-Todd, 1996). Heavy marijuana use has alsobeen associated with an “amotivational syndrome” in adolescents. This name wasgiven to adolescents who seem to lose ambition, but it doesn’t fit the classicalpattern of major depression (Kolansky & Moore, 1975). Laboratory experimentswith humans have been conducted to determine whether marijuana has a specific