Of the 19 papers finalized in our qualitative synthesis, eleven gray matter (n = 4,040), five white matter (n = 319) and three examined both gray and white matter (n = 3,608), where surface area, thickness, and/or volume differences were studied. Assessment of risk of bias for every study using the CASP tool is summarized in Table 1.
Gray Matter:
Of the 14 studies (eleven only gray matter and three gray and white matter) six studies were ROI-based and eight examined the whole brain (Baranger et al., 2020; Brumback et al., 2016; Cheetham et al., 2014; Hatoum et al., 2021; Infante, Courtney, Castro, Squeglia, & Jacobus, 2018; Jacobus et al., 2016; O’Brien & Hill, 2017; Rane et al., 2022; Robert et al., 2020; Seo et al., 2019; Squeglia et al., 2017; Urošević et al., 2015; Wade et al., 2019; Whelan et al., 2014) (Tables 2.1, 2.2, and 4). A total of 8,546 participants were included in the review. Almost all studies used T1W imaging, with the exception of Whelan et al. (imaging technique unknown) and Robert et al. (voxel-based and tensor-based morphometry) (Robert et al., 2020; Whelan et al., 2014). Sex ratio was roughly divided in half, with the biggest difference present in the Brumback et al. study (154 males: 111 females; 58%:42%) (Brumback et al., 2016). The shortest follow-up duration was up to two years (Urošević et al., 2015; Whelan et al., 2014), and the longest was up to 13 years (Brumback et al., 2016; Wade et al., 2019). Mean baseline age ranged between 12.7 to 16.5 (Cheetham et al., 2014; Urošević et al., 2015). The following brain regions were mostly implicated in predicting future problematic alcohol use: occipital lobe, frontal lobe, cerebellum, and temporal cortex, anterior cingulate cortex, dorsolateral prefrontal cortex, superior frontal gyrus, precentral gyrus, superior parietal lobe, and supramarginal gyrus. In addition, changes in left nucleus accumbens, prefrontal and subcortical regions, and right dorsolateral prefrontal cortex and insula were implicated in alcohol initiation in adolescents.
Whelan et al. utilized machine learning and created models of adolescent binge drinking via extracted data from the IMAGEN project (Whelan et al., 2014). They found that right middle and precentral gyri (Brodmann area 6) and bilateral superior frontal gyrus (Brodmann area 9) are the regions with the strongest prediction of future episodes of problematic drinking (Whelan et al., 2014). It is notable to mention that structural factors that predicted future problematic alcohol use were gray matter volume, total parenchymal volume, as well as gray: white matter ratio.
Rane et al. identified an association between several gray matter areas, particularly in the occipital lobe, and future problematic drinking (Rane et al., 2022). Features from the frontal lobe, cerebellum, and temporal cortex were also of utility in predicting problematic drinking. In the occipital lobe, participants with problematic drinking predictions had lower grey matter thickness in the right-cuneus, lateral occipital, and pericalcarine cortices, and higher curvature index in left-cuneus and left-pericalcarine cortex. In the frontal lobe, the left-frontal pole and right-precentral gyrus were relevant clusters for future prediction analyses (including from age 14 to 22). In the temporal lobe, the left inferior temporal gyrus and increased left temporal pole volume were relevant. Finally, increased right cerebellum cortex volume was relevant in prediction analyses. Other relevant features included increased right inferior parietal cortex volume, increased right parahippocampal gyrus area, lower left rostral middle frontal gyrus standard deviation of thickness, and lower integrated rectified mean curvature of the right bank of the superior temporal sulcus (Rane et al., 2022). A full list of structures is available in Table 4.
Cheetham et al. discovered that smaller left paralimbic anterior cingulate cortex volumes predicted problematic drinking (Cheetham et al., 2014). Interestingly, they did not discover such predictive properties in the amygdala, hippocampus, and the orbitofrontal cortex. Urosevic et al. showed that participants with smaller left nucleus accumbens at baseline had a higher likelihood of initiating alcohol and drug use during follow-up (Urošević et al., 2015). Moreover, similar to the Cheetham et al. study, this study did not identify the amygdala and orbitofrontal cortex as predictors of problematic drinking either. However, the more recent O’Brien and Hill’s study found that orbitofrontal cortex to amygdala volume ratio is a significant predictor of alcohol and drug use disorders (O’Brien & Hill, 2017). This study also showed that prefrontal and subcortical morphology correlates with adolescents’ age of onset of substance use with and without a family history of substance use disorders.
Brumback et al. showed that dorsolateral prefrontal cortex surface area predicts binge drinking frequency, and that smaller brain surface area is inversely associated with more binge drinking (Brumback et al., 2016).
Jacobus et al. demonstrated that group by time interaction effects predicted cortical thickness in 18 regions in both left and right hemispheres (Jacobus et al., 2016). At baseline, in the left hemisphere, the group that later engaged in problematic drinking over time showed significantly thicker cortices in frontal and parietal areas, such as the left superior frontal gyrus, precentral gyrus, superior parietal lobe, and supramarginal gyrus. The more recent Infante et al. study from the same team showed that significant group differences exist in frontal, parietal and temporal lobes before and after alcohol initiation (Infante et al., 2018). Bilateral medial orbitofrontal cortex and right insula showed surface area reduction in all groups (control, alcohol, and alcohol + cannabis groups). Moreover, the group that initiated problematic drinking had more surface area decreases in the same regions compared to the other groups.
Squeglia et al. identified a total of 34 predictors of alcohol consumption (Squeglia et al., 2017). Of these, 15 predictors were pertinent to structural brain regions. In a decreasing order of importance, decreased cortical thickness in each of the following areas significantly predicted which participants, from 12 to 14 years of age, would initiate moderate to heavy alcohol use by 18: left supramarginal, left transverse temporal, right pars orbitalis, right superior parietal, right precuneus, right temporal pole, right frontal pole, and left superior parietal cortex. Moreover, the study identified several areas with decreased cortical thickness that, although not individually a significant predictor, would each contribute significantly to the predictive model when allowed to interact with other neuroanatomical variables. These regions were, in a decreasing order of importance, the following: right rostral middle frontal, left lingual, left lateral occipital, left rostral anterior cingulate, right middle temporal, left banks superior temporal sulcus, and right superior frontal.
A study conducted by Wade et al., which primarily studied alcohol and cannabis co-consumption, demonstrated significance in the left lateral orbitofrontal cortex (Wade et al., 2019). However, when examining the alcohol-only cohort, the researchers discovered no significance in the lateral orbitofrontal cortex volume as a predictor of future adolescent problematic drinking (Wade et al., 2019). This was also the case when analyzing results at both the surface area and cortical thickness levels.
Robert et al. showed that accelerated gray matter atrophy rates in the temporal cortices (left and right posterior) and left prefrontal cortex were associated with increased alcohol intoxication (i.e. drunkenness) frequency (Robert et al., 2020). The study suggested a directionality as determined by gray matter atrophy in late binge drinkers compared with non-drinking controls. Seo et al.’s study on the other hand, was the only study that showed no significant differences in gray matter volume between 19-year-old heavy and light drinkers in 24 different brain regions assessed at 14 years of age (Seo et al., 2019).
Results by Baranger et al.’s study highlighted that smaller right dorsolateral prefrontal cortex and insula gray matter volumes predict adolescent alcohol initiation and its future usage during adulthood (Baranger et al., 2020). Moreover, volume reduction in dorsolateral prefrontal cortex served as a predictor of problematic drinking initiation in adolescents who were alcohol naïve at baseline (Baranger et al., 2020).
Finally, Hatoum and colleagues used mixed effects models to determine whether there is an association between polygenic risk scores for both problematic alcohol (PAU-PRS) and drinks per week (DPW-PRS), and changes in cortical gray matter in substance naïve adolescents of European ancestry and those of African ancestry (Hatoum et al., 2021). They found a correlation with PAU-PRS scores and decreased left frontal pole gray matter volume and greater right supramarginal gyrus cortical thickness in the European Ancestry, but no significant association was observed in any of the brain regions for individuals of African ancestry (Hatoum et al., 2021).
White Matter:
Of the eight studies (five only white matter and three white and gray matter) four studies were ROI-based and four examined the whole brain (Chung & Clark, 2014; Hatoum et al., 2021; Jacobus et al., 2013; Jones & Nagel, 2019; Morales, Jones, Harman, Patching-Bunch, & Nagel, 2020; Rane et al., 2022; Squeglia, Rinker, et al., 2014; Wade et al., 2019) (Tables 3.1, 3.2, and 4). A total of 818 participants were included in the review. A total of three structural imaging techniques were used in the studies combined: DTI, T1W, and DWI. Three studies had <40% female participants (Chung & Clark, 2014; Jacobus et al., 2013; Squeglia, Rinker, et al., 2014). The shortest follow-up duration was up to one year (Chung & Clark, 2014), and the longest was up to 13 years (Wade et al., 2019). Mean baseline age ranged from 13.5 to 17.5 (Jacobus et al., 2013; Jones & Nagel, 2019; Wade et al., 2019). The following brain areas and measures were implicated in predicting future problematic alcohol use: corpus callosum, left insula, midbrain, internal capsule, posterior, fornix, and superior corona radiata, left ventral diencephalon, left inferior and middle temporal gyrus, left caudate, brainstem, frontal cortices, fronto-striatal fractional anisotropy values, medial orbital gyrus, prefrontal cortex, and ventral pallidum.
Rane et al. found several white matter tracts to be of predictive value in future problematic drinking. These include parts of the corpus callosum (e.g., anterior corpus callosum and splenium), internal capsule, and posterior corona radiata, with all these tracts, as well as the brain stem, being found to have lower-than-average intensities (Rane et al., 2022).
In Jacobus et al.’s study, poorer white matter integrity was identified as a potential predictor of problematic alcohol and cannabis use among adolescents (Jacobus et al., 2013). More specifically, the limbic and projection-fiber pathways in the fornix and superior corona radiata predicted risky behaviors.
Chung and Clark’s study found that left insula white matter volume was positively correlated with binge drinking frequency (Chung & Clark, 2014). In addition, right insula white matter volume was correlated with alcohol craving/obsession; left insula white matter volume was not. Interestingly, left insula white matter volume was positively correlated with current alcohol abuse/symptom frequency at 1 year, whereas right insula white matter volume was not correlated. Overall, the study showed that left insula white matter volume indirectly predicted binge drinking frequency.
Squeglia et al.’s findings indicated pre-existing volume differences in frontal brain regions in future drinkers and brain volume reduction in subcortical and temporal regions after the initiation of drinking (Squeglia, Rinker, et al., 2014). The specific regions where adolescent problematic drinkers showed greater volume reductions than demographically matched controls over the 3-year follow-up period were the left ventral diencephalon, left inferior and middle temporal gyrus, left caudate, and brainstem. A negative correlation was present between these volumetric changes and the lifetime alcohol use as well as peak number of drinks on one occasion in the past year. This indicates a dose-dependent effect of alcohol and cannabis on cortical thinning. Baseline group differences were present in several frontal cortical volumes. Specifically, adolescents who initiated heavy drinking at 3-year follow-up exhibited smaller cortical volume in three frontal regions, as well as less cerebellar white matter volume, when compared to control adolescents who also participated in the follow-up study. Overall, these findings demonstrate heavy drinking adolescents have subtle brain abnormalities that are present prior to the onset of drinking.
More recently, Jones and Nagel’s study showed that less white matter volume was detected prior to alcohol use in adolescents that develop binge-drinking (Jones & Nagel, 2019). Additionally, the fractional anisotropy values were greater in future binge-drinking adolescents when compared to controls in white matter regions in the midbrain and internal capsule, which may represent a predisposition to engage in future drinking. On the other hand, the lower fractional anisotropy values detected previously in binge-drinking adolescents compared to controls may have been due to the neurotoxic effects of alcohol. In the early stages of adolescence, prior to the initiation of drinking, future binge drinking was associated with changes in the fronto-striatal fractional anisotropy values that surround subcortical regions, and mean diffusivity in fronto-cortical regions. However, many of these changes were shown to be transient and attenuate by late stages of adolescence.
Morales et al. showed that adolescent binge drinkers have abnormalities in white matter microstructure by providing evidence of premorbid differences in fractional anisotropy (lower medial orbital gyrus), which are also associated with the amount of time taken until the onset of binge drinking (Morales et al., 2020). Additionally, a delayed maturation of prefrontal white matter was also present, which was associated with less top-down control over striatal sensitivity to reward. Moreover, individual differences in white matter proximal to ventral pallidum were also present.
Hatoum et al. examined 36 white matter tracts and 26 subcortices of alcohol naïve adolescents of European and African ancestries and did not find any significant association between them and polygenic risk scores for both problematic alcohol (PAU-PRS) and drinks per week (DPW-PRS) (Hatoum et al., 2021).
Moderating Factors
Other factors that may moderate the relationship between neuroanatomical variables and future problematic alcohol use among adolescents include familial history, sex differences, cannabis use, and personality. Familial history is a factor that was identified in several of the examined studies as a predictor of problematic drinking. For example, O’Brien and Hill’s study indicated that familial risk status is a significant predictor of alcohol and drug use disorder (O’Brien & Hill, 2017). In addition, Jones and Nagel’s study showed that family history of alcoholism was associated with changes in the fronto-striatal fractional anisotropy values that surround cortical regions, and mean diffusivity in fronto-cortical regions (Jones & Nagel, 2019). However, the study noted that the attenuation of the changes by the late stages of adolescence indicated that familial history of alcoholism is only partially associated with the fractional anisotropy and mean diffusivity changes.
In Robert et al.’s study, accelerated gray matter atrophy rates in the temporal cortices (left and right posterior) and left prefrontal cortex were associated with an increased frequency of drunkenness in males more than females (Robert et al., 2020). In Seo et al.’s study, at age 19, female heavy drinkers had gray matter atrophy associations in cue reactivity relevant brain regions (Seo et al., 2019). Negative life events at 19, but not 14, were shown to be positively correlated with heavy drinking in both sexes.
Cannabis use is another factor that could have partially influenced the results. For example, Jacobus et al.’s study showed that at baseline, in the right hemisphere, those who only engaged in problematic drinking had thicker cortices in frontal and parietal regions such as the precentral gyrus, paracentral gyrus, rostral middle frontal gyrus, superior frontal gyrus, para triangularis, and insula cortex when compared to those who engaged in both problematic alcohol and cannabis consumption (Jacobus et al., 2016).
With regards to personality differences, Seo et al.’s study showed that agreeableness (both sexes) and conscientiousness (males only) were negatively correlated with the heavy drinking group, and hopelessness (females only) was positively correlated with the heavy drinking group (Seo et al., 2019). In addition, Cheetham et al. showed that problematic drinking was associated with higher levels of negative temperamental affectivity (Cheetham et al., 2014). However, no relationship was established between this finding and their other finding that determined the predictive role of anterior cingulate cortex in problematic drinking.