Slower processing speed has also been identified among heavy marijuana using youth , even after one month of monitored abstinence .In sum, adolescents seem to show modest but significant deficits in cognition across multiple domains. In the area of executive functioning, adolescent drinkers show worse decision making and inhibitory control, whereas adolescent marijuana users show worse flexible thinking and more perseverative errors. The area of visuospatial functioning appears especially sensitive to heavy alcohol use as adolescent heavy drinkers show worse spatial operations, block design, complex figure copying, and pattern recognition. Both adolescent alcohol and marijuana users show similar deficits in verbal and nonverbal learning and memory, worse attention, slower psychomotor speed, and lower IQ. Taken in concert, these group findings suggest neuropsychological differences across multiple domains in both heavy alcohol and marijuana using adolescents. Since much of what has been reviewed to this point discusses group findings in the animal and human literature, trim tray it is important to now consider what potential aspects of substance use may contribute most strongly to observed differences. Each substance use characteristic is examined and any association described in the extant literature between that characteristic and a group finding is provided.
As binge drinking and heavy marijuana use are so prevalent among adolescents, it is important to consider studies’ efforts to correlate observed impairments with recent exposure to high quantities of alcohol or of marijuana . Animalresearch indicates that recent exposure to high doses of ethanol results in neurodegeneration of the corticolimbic circuit and more perseverative errors on a spatial learning task . Studies have shown that recent consumption of large amounts of alcohol correlates with reduced white matter integrity in the splenium . Among adolescents, more frequent consumption of alcohol correlates with poorer visuospatial task performance in complex figure delay for females and in block design for all participants . Frequent, heavy use of alcohol was also related to neuropsychological performance over time, with more frequent drinking associated with worse visuospatial memory and verbal short-term memory task performance . Similar to findings for alcohol, studies examining marijuana using youth also found correlations between greater frequency of marijuana use and worse performance on tasks of learning and memory . Smaller right hippocampal volumes were also correlated with greater self-reported cannabis use and with more weekly cannabis use .Age of onset is an important correlate with alcohol-related outcomes as earlier age of drinking onset is associated with greater likelihood of alcohol toxicity induced disruptions in developing brain regions, particularly the frontal lobe , greater lifetime risk for developing alcohol dependence , and elevated risk for myriad social and mental health problems . It is interesting to note that while earlier age of onset relates to long-term alcohol use disorders and worse outcomes, studies have not found consistent correlations between age of onset of drinking and neuroanatomical and neurocognitive measures.
An initial study found a positive correlation between age of onset and hippocampal volume , but a later study failed to replicate that finding . One study found that participants who initiated binge drinking at an earlier age had worse decision making on a gambling task . Age of onset of marijuana use, however, appears strongly related to multiple findings. Age of initiation of marijuana use correlates positively with prefrontal cortex volume, with younger age of first use associating with reduced volume . Alterations of cortical thickness are also related to younger age of initiation of cannabis . Earlier age of onset of marijuana use has also been associated with worse visual scanning performance ; decreases in verbal IQ, verbal recall, and use of semantic categories ; and poorer performance on tasks of sustained attention, impulse control, and executive functioning .When examining the effects of a substance on a developing adolescent brain, it is important to consider the impact of cumulative exposure measured as either total lifetime episodes or years of abuse or dependence. Several studies have identified associations between lifetime drinking episodes and structural, functional, and neurocognitive outcomes. Among adolescents, longer duration of heavy drinking was related to decreased white matter integrity in the corpus callosum , and those with longer lasting AUDs had smaller hippocampi . Lifetime drinking episodes have also been found to correlate with several neurocognitive outcomes. Among adolescents with AUD, greater lifetime consumption correlated with increased perseveration errors on a verbal memory task and worse attention functioning . Among marijuana using adolescents, severity of use has been linked to worse performance on tasks of learning and recall .The correlations between withdrawal and neuroanatomical and neurocognitive outcomes have been examined most extensively in the adolescent alcohol literature. Acute effects of high dose alcohol exposure continue to be experienced in the day or two following alcohol consumption. In adolescents, these effects include headaches, muscle aches or weakness, feeling weak or faint when standing, heart racing, feeling depressed or irritable, nausea, vomiting, sweating, trouble sleeping, or tremor and shaking .
Additionally, youth who develop physical addiction to alcohol can experience alcohol related seizures in the first few days of abstinence . Hangover and withdrawal symptoms are very common following binge drinking and appear to be strongly related to cognitive impairments among teens who frequently binge drink . A body of compelling evidence suggests that it is the repeated withdrawal from alcohol that may be responsible for many of the central nervous system effects of chronic alcohol exposure and that repeated withdrawal from alcohol provokes cognitive impairments . In animals, repeated withdrawal from alcohol resulted in higher rates of seizures during withdrawal than were observed after continuous exposure over the same duration, suggesting a strong association between repeated withdrawals and withdrawal seizure susceptibility .Negative affective states – including hyperirritability, depression, and anxiety that commonly occur among those experiencing post alcohol effects and impact neurocognitive performance – seem to maintain alcohol consumption and promote relapse . The severity of withdrawal-like symptoms is an important indication of neuropsychological impairments in detoxified human adolescents and young adults, which makes the examination of withdrawal’s relation to impairments warranted . Research needs to address whether impairments are likely caused by alcohol itself, by negative affective states provoked by alcohol, or by damage caused by repeated withdrawals. The research is largely consistent in its findings about the relationship between lifetime withdrawal and neuroanatomical and neurocognitive outcomes. Withdrawal experience does not seem to correlate with reduced hippocampal volumes , while it does correlate with reductions in white matter integrity and neuropsychological deficits. Among youth with AUDs, reduced white matter integrity in the corpus callosum was significantly related to the number of alcohol withdrawal symptoms . Among subclinical, binge drinking teens, those with more hangover symptoms showed more compromised white matter in the body and genu of the corpus callosum, frontal lobe projection fibers, and cerebellar tracts . Of note, among adult alcoholics, alcohol-related seizures were associated with smaller white matter volumes in the temporal lobe, suggesting cumulative effects of these withdrawal experiences .Among adolescents with alcohol use disorders, those with more withdrawal symptoms performed worse on tasks of working memory , visuospatial functioning , delayed verbal retention , and attention . Lifetime withdrawal predicted attention and visuospatial functioning at year 8 of a longitudinal study . Withdrawal scores also predicted slower DVT completion times for males, which suggests that withdrawal and hangover symptoms significantly predict deterioration of attention skills in boys who initiate heavy drinking . Recent withdrawal is also important to consider as a potential contributor to brain changes and neuropsychological deficits. Associations between neuroanatomical and neurocognitive measures of interest and recent withdrawal are consistent with findings for lifetime withdrawal. Among youth with AUDs, trim tray with screen those who reported more withdrawal symptoms in the prior three months showed poorer visuospatial abilities, working memory, and attention – even after controlling for gender, history of head injury or learning disability, socioeconomic status , and grades completed .
Similarly, the number of substance withdrawal symptoms in the three months prior to neuropsychological testing significantly predicted verbal learning, recall, and recognition with greater withdrawal negatively affecting immediate, delayed, and recognition memory performance among youth followed over a ten year period . Both lifetime and recent withdrawal showed relationships with poorer visuospatial functioning, memory, and attention. Lifetime withdrawal symptoms may reflect distinct, negative effects on brain functioning, with a particular impact on white matter integrity and on memory and visuospatial functioning.It is important at this time to reflect on some of the methodological limitations of the aforementioned studies. As these studies were done on adolescents after their initiation of alcohol and/or marijuana use, it is not possible to determine if their substance use led to their neuroanatomical and neurocognitive deficits or if those with lower cognitive functioning have a propensity to drink alcohol or smoke marijuana. This issue emphasizes the need for studies to utilize prospective designs to collect data on participants in late childhood or early adolescence and follow them through adolescence. Alternatively, efforts to match groups on aspects of their premorbid functioning would also be warranted. Also of note, in both the adult and adolescent literature of neuroanatomical and neuropsychological outcomes, abstinence periods vary widely , thereby making direct comparisons challenging and leaving unclear the chronicity of cognitive changes among alcohol and marijuana using youth.It is also important to consider differences between clinical and subclinical populations, as much of the original research in the field was conducted on teens in clinical settings. Those in treatment both for alcohol and for marijuana manifest more severe substance use disorders and tend to have poorer cognitive, behavioral, and social functioning . So while more recent efforts to recruit from the community may be more generalizable to the population of adolescent users, these youth may be higher functioning than those in treatment programs. In general, heavy users of alcohol and/or marijuana are also more likely to have other comorbid disorders, making it difficult to disentangle unique effects attributable to the substance distinct from mood, anxiety, or attentional features, unless specific efforts are made by researchers to consider such differences in analyses. While multiple studies reviewed have reported neuroanatomical and neuropsychological differences in alcohol and marijuana using teens, even after one month of abstinence, another limitation across these studies is the high rate of comorbid substance use. Many alcohol-using populations have moderate to high levels of marijuana use; similarly, many marijuana-using teens have significant exposure to heavy drinking. Therefore, much of the existing literature cannot report confidently if cognitive decrements are primarily related to alcohol, marijuana, or to use of both substances. Until this point, studying users of mainly alcohol or mainly marijuana may have limited sample size in a population that is already difficult to recruit and study; so many users studied also have use of other substances. Additionally, the existing literature predominately compares alcohol users to nonusers or marijuana users to nonusers. Existing investigations have not compared alcohol users and marijuana users directly to each other.This review inspired three investigations to address specific areas previously unexplored in the extant literature and/or limitations in the existing research. The first study aimed to make a contribution to the literature on the affective vulnerability processes governing alcohol misuse among adolescents by investigating the rate and pattern of changes in emotional reactivity and distress tolerance during the initial days to weeks of abstinence from alcohol in heavy drinking youth. Adult research has demonstrated improvements in mood with sustained abstinence that contribute to decreased emotional reactivity and improved distress tolerance, but this possibility had not yet been explored in adolescent populations. Many researchers have examined relapse phenomena via self-report outside of a relapse risk context, either using retrospective report of previous relapse events or in the context of longitudinal studies that utilize prospective reports , yet without proximity to the additive impact of stress. This study introduced an objective stressor to examine affective response, cognitive performance, and distress tolerance in heavy episodic drinking and non-drinking adolescents and to assess potential group differences and determine whether affective reactivity, performance, and distress tolerance improve over a four-week period following cessation of substance use in the heavy drinking youth. The utilization of the PASAT-C task created an opportunity to test a negative reinforcement model by employing a behavioral measure that provides measurable responses in close proximity to a stressor. The second study hoped to fill a void in the existing literature by examining neuropsychological functioning during early abstinence in adolescents with histories of heavy episodic drinking as compared to well-matched controls.