Dual tasking and working memory in alcoholism: relation to frontocerebellar circuitry

Characterization of South African adolescents with alcohol use disorders but without psychiatric or polysubstance comorbidity

BACKGROUND

Individuals who begin drinking during early adolescence and exhibit externalizing pathology and disinhibitory/dysregulatory tendencies are more vulnerable to developing alcohol use disorders (AUDs) in adulthood. Previous research has focused on in-treatment populations with substantial comorbid psychopathology and polysubstance use. Here, we characterize a unique sample of treatment-naïve adolescents without such comorbidity to help identify vulnerable youth who may benefit from early intervention.

METHODS

We compared externalizing propensity, disinhibitory characteristics, and school performance in adolescents with AUDs (but without comorbid psychopathology or other substance use; n = 70) to those of demographically matched controls (n = 70). Within the AUD group, we compared measures of substance use and the disinhibitory syndrome between boys and girls with differing severity of externalizing propensity.

RESULTS

Adolescents with AUDs demonstrated more externalizing propensity and disinhibitory personality traits (impulsivity, novelty seeking, and excitement seeking), poorer self-monitoring and response inhibition, more bullying and sexual risk-taking behavior, poorer first-language performance, and greater use of alcohol, cannabis, and nicotine (p < 0.05). Within the AUD group, participants with higher externalizing propensity began drinking earlier, more frequently, and for a longer duration than those with lower externalizing symptoms (p < 0.05). Disinhibitory features (personality, cognition, and behavior) were, however, not stronger in those with higher externalizing propensity.

CONCLUSIONS

We suggest that the constructs of externalizing propensity and disinhibitory syndrome are useful in characterizing treatment-naïve adolescents with AUDs but without comorbid psychopathology or polysubstance use. These results support the importance of these constructs in understanding adolescent AUDs, even when the frank externalizing diagnoses of childhood (oppositional defiant disorder and conduct disorder) are excluded.

Adolescent binge drinking linked to abnormal spatial working memory brain activation: differential gender effects

BACKGROUND

Binge drinking is prevalent during adolescence, and its effect on neurocognitive development is of concern. In adult and adolescent populations, heavy substance use has been associated with decrements in cognitive functioning, particularly on tasks of spatial working memory (SWM). Characterizing the gender-specific influences of heavy episodic drinking on SWM may help elucidate the early functional consequences of drinking on adolescent brain functioning.

METHODS

Forty binge drinkers (13 females, 27 males) and 55 controls (24 females, 31 males), aged 16 to 19 years, completed neuropsychological testing, substance use interviews, and an SWM task during functional magnetic resonance imaging.

RESULTS

Significant binge drinking status × gender interactions were found (p < 0.05) in 8 brain regions spanning bilateral frontal, anterior cingulate, temporal, and cerebellar cortices. In all regions, female binge drinkers showed less SWM activation than female controls, while male bingers exhibited greater SWM response than male controls. For female binge drinkers, less activation was associated with poorer sustained attention and working memory performances (p < 0.025). For male binge drinkers, greater activation was linked to better spatial performance (p < 0.025).

CONCLUSION

Binge drinking during adolescence is associated with gender-specific differences in frontal, temporal, and cerebellar brain activation during an SWM task, which in turn relate to cognitive performance. Activation correlates with neuropsychological performance, strengthening the argument that blood oxygen level-dependent activation is affected by alcohol use and is an important indicator of behavioral functioning. Females may be more vulnerable to the neurotoxic effects of heavy alcohol use during adolescence, while males may be more resilient to the deleterious effects of binge drinking. Future longitudinal research will examine the significance of SWM brain activation as an early neurocognitive marker of alcohol impact to the brain on future behaviors, such as driving safety, academic performance, and neuropsychological performance.

Disruption of functional connectivity of the default-mode network in alcoholism

The default mode network (DMN) comprises brain structures maximally active at rest. Disturbance of network nodes or their connections occurs with some neuropsychiatric conditions and may underlie associated dysfunction. DMN connectivity has not been examined in alcoholism, which is marked by compromised DMN nodes and impaired spatial working memory. To test whether performance would be related to DMN integrity, we examined DMN functional connectivity using functional magnetic resonance imaging (fMRI) data and graph theory analysis. We assumed that disruption of short paths between network nodes would attenuate processing efficiency. Alcoholics and controls were scanned at rest and during a spatial working memory task. At rest, the spontaneous slow fluctuations of fMRI signals in the posterior cingulate and cerebellar regions in alcoholics were less synchronized than in controls, indicative of compromised functional connectivity. Graph theory analysis indicated that during rest, alcoholics had significantly lower efficiency indices than controls between the posterior cingulate seed and multiple cerebellar sites. Greater efficiency in several connections correlated with longer sobriety in alcoholics. During the task, on which alcoholics performed on par with controls, connectivity between the left posterior cingulate seed and left cerebellar regions was more robust in alcoholics than controls and suggests compensatory networking to achieve normal performance.

Contributions of studies on alcohol use disorders to understanding cerebellar function

Neuropathological, neuropsychological, and neuroimaging studies of human alcoholism provide evidence for degradation of frontal, pontine, thalamic, and cerebellar brain sites and disturbed associated functions. Current studies using neuroimaging combined with examination of executive functions, traditionally considered the sole purview of the frontal lobes, have identified a role for the cerebellum serving as a compensatory processing adjunct to enable normal performance on challenging tasks tapping executive functions. This overview proposes that disruption of an executive frontocerebellar network is a major contributor to characteristic behaviors of alcoholism that, on the one hand, enable alcohol use disorders, and on the other hand, lead to compensation for dysfunctions in alcoholism traditionally considered frontally-based.

Cerebral blood flow in posterior cortical nodes of the default mode network decreases with task engagement but remains higher than in most brain regions

Functional neuroimaging studies provide converging evidence for existence of intrinsic brain networks activated during resting states and deactivated with selective cognitive demands. Whether task-related deactivation of the default mode network signifies depressed activity relative to the remaining brain or simply lower activity relative to its resting state remains controversial. We employed 3D arterial spin labeling imaging to examine regional cerebral blood flow (CBF) during rest, a spatial working memory task, and a second rest. Change in regional CBF from rest to task showed significant normalized and absolute CBF reductions in posterior cingulate, posterior-inferior precuneus, and medial frontal lobes . A Statistical Parametric Mapping connectivity analysis, with an a priori seed in the posterior cingulate cortex, produced deactivation connectivity patterns consistent with the classic "default mode network" and activation connectivity anatomically consistent with engagement in visuospatial tasks. The large task-related CBF decrease in posterior-inferior precuneus relative to its anterior and middle portions adds evidence for the precuneus' heterogeneity. The posterior cingulate and posterior-inferior precuneus were also regions of the highest CBF at rest and during task performance. The difference in regional CBF between intrinsic (resting) and evoked (task) activity levels may represent functional readiness or reserve vulnerable to diminution by conditions affecting perfusion.