Smoking and the developing brain: altered white matter microstructure in attention-deficit/hyperactivity disorder and healthy controls

Adolescent substance use initiation and long-term neurobiological outcomes: insights, challenges and opportunities

The increased frequency of risk taking behavior combined with marked neuromaturation has positioned adolescence as a focal point of research into the neural causes and consequences of substance use. However, little work has provided a summary of the links between adolescent initiated substance use and longer-term brain outcomes. Here we review studies exploring the long-term effects of adolescent-initiated substance use with structural and microstructural neuroimaging. A quarter of all studies reviewed conducted repeated neuroimaging assessments. Long-term alcohol use, as well as tobacco use were consistently associated with smaller frontal cortices and altered white matter microstructure. This association was mostly observed in the ACC, insula and subcortical regions in alcohol users, and for the OFC in tobacco users. Long-term cannabis use was mostly related to altered frontal cortices and hippocampal volumes. Interestingly, cannabis users scanned more years after use initiation tended to show smaller measures of these regions, whereas those with fewer years since initiation showed larger measures. Long-term stimulant use tended to show a similar trend as cannabis in terms of years since initiation in measures of the putamen, insula and frontal cortex. Long-term opioid use was mostly associated with smaller subcortical and insular volumes. Of note, null findings were reported in all substance use categories, most often in cannabis use studies. In the context of the large variety in study designs, substance use assessment, methods, and sample characteristics, we provide recommendations on how to interpret these findings, and considerations for future studies.

Neurite Orientation Dispersion and Density Imaging (NODDI) of Brain Microstructure in Adolescent Cannabis and Nicotine Use

INTRODUCTION

Despite evidence suggesting deleterious effects of cannabis and nicotine tobacco product (NTP) use on white matter integrity, there have been limited studies examining white matter integrity among users of both cannabis and nicotine. Further, updated white matter methodology provides opportunities to investigate use patterns on neurite orientation dispersion and density (NODDI) indices and subtle tissue changes related to the intra- and extra-neurite compartment. We aimed to investigate how cannabis and NTP use among adolescents and young adults interacts to impact the white matter integrity microstructure.

MATERIALS AND METHODS

A total of 221 participants between the ages of 16 and 22 completed the Customary Drinking and Drug Use Record (CDDR) to measure substance use, and underwent a magnetic resonance imaging (MRI) session. Participants were divided into NTP-control and NTP groupings and cannabis-control and cannabis groupings (≥26 NTP/cannabis uses in past 6 months). Tract-Based Spatial Statistics (TBSS) and two-way between-subjects ANOVA investigated the effects of NTP use group, cannabis use group, and their interaction on fractional anisotropy (FA) and NODDI indices while controlling for age and biological sex.

RESULTS

NTP use was associated with decreased FA values and increased orientation dispersion in the left anterior capsule. There were no significant effects of cannabis use or the interaction of NTP and cannabis use on white matter outcomes.

DISCUSSION

NTP use was associated with altered white matter integrity in an adolescent and young adult sample. Findings suggest that NTP-associated alterations may be linked to altered fiber tract geometry and dispersed neurite structures versus myelination, as well as differential effects of NTP and cannabis use on white matter structure. Future work is needed to investigate how altered white matter is related to downstream behavioral effects from NTP use.

The interaction effects of age, APOE and common environmental risk factors on human brain structure

Mounting evidence suggests considerable diversity in brain aging trajectories, primarily arising from the complex interplay between age, genetic, and environmental risk factors, leading to distinct patterns of micro- and macro-cerebral aging. The underlying mechanisms of such effects still remain unclear. We conducted a comprehensive association analysis between cerebral structural measures and prevalent risk factors, using data from 36,969 UK Biobank subjects aged 44-81. Participants were assessed for brain volume, white matter diffusivity, Apolipoprotein E (APOE) genotypes, polygenic risk scores, lifestyles, and socioeconomic status. We examined genetic and environmental effects and their interactions with age and sex, and identified 726 signals, with education, alcohol, and smoking affecting most brain regions. Our analysis revealed negative age-APOE-ε4 and positive age-APOE-ε2 interaction effects, respectively, especially in females on the volume of amygdala, positive age-sex-APOE-ε4 interaction on the cerebellar volume, positive age-excessive-alcohol interaction effect on the mean diffusivity of the splenium of the corpus callosum, positive age-healthy-diet interaction effect on the paracentral volume, and negative APOE-ε4-moderate-alcohol interaction effects on the axial diffusivity of the superior fronto-occipital fasciculus. These findings highlight the need of considering age, sex, genetic, and environmental joint effects in elucidating normal or abnormal brain aging.

Exploring Contributing Factors of Solitary Drinking among Hong Kong Chinese Adolescents and Young Adults: A Descriptive Phenomenology

Adolescents and young adults mostly drink alcohol because of social activities. However, some drink outside of normative social contexts, exhibiting a behaviour pattern known as solitary drinking. Increasing evidence indicates that solitary drinking is strongly associated with problematic drinking in adolescents and young adults. However, it remains unclear why individuals initiate and maintain this drinking habit. To address this gap in the existing literature, the current study explored the factors contributing to solitary drinking in this population. Descriptive phenomenology was used. A convenience sample of 44 solitary drinkers aged between 10 and 24 were invited to undergo individual semi-structured interviews. All interviews were audio-recorded and transcribed verbatim. The data were analysed by two researchers separately using Colaizzi’s method. Using qualitative descriptions, the following factors were identified as explaining the initiation and continuation of solitary drinking among adolescents and young adults: (1) enhancement and coping drinking motives, (2) social discomfort, (3) reduced self-control, (4) automatic mental process, and (5) a desperate response to stressors. Since reduced self-control plays an important role in long-term addiction, future studies should be conducted to determine potential applications of mindfulness-based interventions to improve self-control, which may prevent the progression from solitary drinking to alcohol use disorder.

The Effects of Nicotine and Cannabis Co-Use During Late Adolescence on White Matter Fiber Tract Microstructure

OBJECTIVE

Co-use of cannabis and nicotine and tobacco products (NTPs) in adolescence/young adulthood is common and associated with worse outcomes than the use of either substance in isolation. Despite this, little is known about the unique contributions of co-use to neurostructural microstructure during this neurodevelopmentally important period. This study sought to investigate the interactive effects of nicotine and cannabis co-use on white matter fiber tract microstructure in emerging adulthood.

METHOD

A total of 111 late adolescent (16-22 years old) nicotine (NTP; n = 55, all past-year cannabis users) and non-nicotine users (non-NTP; n = 56, 61% reporting cannabis use in the past year) completed demographic and clinical interviews and a neuroimaging session comprising anatomical and diffusion-weighted imaging scans. Group connectometry analysis identified white matter tracts significantly associated with the interaction between nicotine group and past-year cannabis use according to generalized fractional anisotropy (GFA).

RESULTS

Nicotine Group × Cannabis Use interactions were observed in the right and left cingulum and left fornix tracts (false discovery rate = 0.053), where greater cannabis use was associated with increased GFA in the cingulum and left fornix, but only when co-used with nicotine.

CONCLUSIONS

This report represents the first group connectometry analysis in late adolescent/young adult cannabis and/or NTP users. Results suggest that co-use of cannabis and NTPs results in a structurally distinct white matter phenotype as compared with cannabis use only, although to what extent this may change over time with more chronic nicotine and cannabis use remains to be examined in future work.

The Effects of Nicotine and Cannabis Co-Use During Late Adolescence on White Matter Fiber Tract Microstructure

OBJECTIVE

Co-use of cannabis and nicotine and tobacco products (NTPs) in adolescence/young adulthood is common and associated with worse outcomes than the use of either substance in isolation. Despite this, little is known about the unique contributions of co-use to neurostructural microstructure during this neurodevelopmentally important period. This study sought to investigate the interactive effects of nicotine and cannabis co-use on white matter fiber tract microstructure in emerging adulthood.

METHOD

A total of 111 late adolescent (16-22 years old) nicotine (NTP; n = 55, all past-year cannabis users) and non-nicotine users (non-NTP; n = 56, 61% reporting cannabis use in the past year) completed demographic and clinical interviews and a neuroimaging session comprising anatomical and diffusion-weighted imaging scans. Group connectometry analysis identified white matter tracts significantly associated with the interaction between nicotine group and past-year cannabis use according to generalized fractional anisotropy (GFA).

RESULTS

Nicotine Group × Cannabis Use interactions were observed in the right and left cingulum and left fornix tracts (false discovery rate = 0.053), where greater cannabis use was associated with increased GFA in the cingulum and left fornix, but only when co-used with nicotine.

CONCLUSIONS

This report represents the first group connectometry analysis in late adolescent/young adult cannabis and/or NTP users. Results suggest that co-use of cannabis and NTPs results in a structurally distinct white matter phenotype as compared with cannabis use only, although to what extent this may change over time with more chronic nicotine and cannabis use remains to be examined in future work.

White matter microstructure differences in individuals with dependence on cocaine, methamphetamine, and nicotine: Findings from the ENIGMA-Addiction working group

BACKGROUND

Nicotine and illicit stimulants are very addictive substances. Although associations between grey matter and dependence on stimulants have been frequently reported, white matter correlates have received less attention.

METHODS

Eleven international sites ascribed to the ENIGMA-Addiction consortium contributed data from individuals with dependence on cocaine (n = 147), methamphetamine (n = 132) and nicotine (n = 189), as well as non-dependent controls (n = 333). We compared the fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD) of 20 bilateral tracts. Also, we compared the performance of various machine learning algorithms in deriving brain-based classifications on stimulant dependence.

RESULTS

The cocaine and methamphetamine groups had lower regional FA and higher RD in several association, commissural, and projection white matter tracts. The methamphetamine dependent group additionally showed lower regional AD. The nicotine group had lower FA and higher RD limited to the anterior limb of the internal capsule. The best performing machine learning algorithm was the support vector machine (SVM). The SVM successfully classified individuals with dependence on cocaine (AUC = 0.70, p < 0.001) and methamphetamine (AUC = 0.71, p < 0.001) relative to non-dependent controls. Classifications related to nicotine dependence proved modest (AUC = 0.62, p = 0.014).

CONCLUSIONS

Stimulant dependence was related to FA disturbances within tracts consistent with a role in addiction. The multivariate pattern of white matter differences proved sufficient to identify individuals with stimulant dependence, particularly for cocaine and methamphetamine.

Support vector machine based classification of smokers and nonsmokers using diffusion tensor imaging

Despite significant progress in treatments for smoking cessation, smoking continues to be a significant public health concern, especially in young adulthood. Thus, developing a predictive model that can classify and characterize the brain-based biomarkers predicting smoking status would be imperative to improving treatment development. In this study, we applied a support vector machine-based classification method to discriminate 70 young male smokers and 70 matched nonsmokers using their diffusion tensor imaging (DTI) data. The classification procedure achieved an average accuracy of 88.6% and an average area under the curve of 0.95. The most discriminative features that contributed to the classification were primarily located in the sagittal stratum (SS), external capsule (EC), superior longitudinal fasciculus (SLF), anterior corona radiata (ACR) and inferior front-occipital fasciculus (IFOF). The following regression analysis showed a significant negatively correlation between the average RD values of the left ACR (r = -0.247, p = 0.039) and FTND. The average MD values in the right EC (r = -0.254, p = 0.034) and RD values in the right IFOF (r = -0.240, p = 0.046) were inversely associated with pack-years. Our findings indicate that the discriminative white matter (WM) features as brain biomarkers provide great predictive power for smoking status and suggest that machine learning techniques can reveal underlying smoking-related neurobiology.

The Influence of Cannabis and Nicotine Co-use on Neuromaturation: A Systematic Review of Adolescent and Young Adult Studies

Accumulating evidence suggests that the use of cannabis and nicotine and tobacco-related products (NTPs) during the adolescent years has harmful effects on the developing brain. Yet, few studies have focused on the developing brain as it relates to the co-administration of cannabis and NTPs, despite the high prevalence rates of co-use in adolescence. This review aims to synthesize the existing literature on neurocognitive, structural neuroimaging, and functional neuroimaging outcomes associated with cannabis and NTP co-use. A systematic search of peer-reviewed articles resulted in a pool of 1107 articles. Inclusion criteria were 1) data-based study; 2) age range of 13 to 35 years or, for preclinical studies, nonadult subjects; 3) cannabis and NTP group jointly considered; and 4) neurocognitive, structural neuroimaging, or functional neuroimaging as an outcome measure. Twelve studies met inclusion criteria. Consistent with the literature, cannabis and nicotine were found to have independent effects on cognition. The available research on the co-use of cannabis and NTPs demonstrates a potential nicotine-related masking effect on cognitive deficits associated with cannabis use, yet there is little research on co-use and associations with neuroimaging indices. In neuroimaging studies, there is preliminary evidence for hippocampal volume differences in co-users and a lack of evidence for co-use differences related to nucleus accumbens activity during reward processing. Notably, no structural neuroimaging studies were found to examine the combined effects of nicotine and cannabis in adolescent-only populations. Further research, including longitudinal studies, is warranted to investigate the influence of cannabis and NTP co-use on maturation.

The effects of nicotine and cannabis co-use during adolescence and young adulthood on white matter cerebral blood flow estimates

RATIONALE

Co-use of cannabis and nicotine is common among adolescents/young adults and is associated with poorer psychological and physical outcomes, compared with single substance use. Little is known about the impact of co-use on the developing brain.

OBJECTIVES

Preliminary investigation of the effects of nicotine on white matter (WM) cerebral blood flow (CBF) in adolescents/young adults and its potential moderation by cannabis use.

METHODS

Adolescent/young adult (16-22 years old) nicotine and tobacco product users (NTP; N = 37) and non-nicotine users (non-NTP; N = 26) underwent a neuroimaging session comprised of anatomical, optimized pseudo-continuous arterial spin labeling, and diffusion tensor imaging scans. Groups were compared on whole-brain WM CBF estimates and their relation to past-year cannabis use. Follow-up analyses assessed correlations between identified CBF clusters and corresponding fractional anisotropy (FA) values.

RESULTS

Group by cannabis effects were observed in five clusters (voxel-wise alpha < 0.001, cluster-wise alpha < 0.05; ≥ 11 contiguous voxels): non-NTP exhibited positive correlations between CBF and cannabis use in all clusters, whereas no significant relationships were observed for NTP. Greater CBF extracted from one cluster (including portions of right superior longitudinal fasciculus) was associated with reduced FA for non-NTP group only.

CONCLUSIONS

This is the first investigation of WM health as indexed by CBF, and its association with FA, in adolescents/young adults with nicotine and/or cannabis use. Results suggest that cannabis use by itself may be related to increased CBF in WM fiber tracts demonstrating poorer structural intergrity, yet the occurrence of even infrequent NTP use (greater than once per month) appears to diminish this relationship.

The associations of comorbid substance use disorders and psychiatric conditions with adolescent brain structure and function: A review

Adolescence is a period of rapid neural and behavioral development that often precipitates substance use, substance use disorders (SUDs), and other psychopathology. While externalizing disorders have been closely linked to SUD epidemiologically, the comorbidity of internalizing disorders and SUD is less well understood. Neuroimaging studies can be used to measure structural and functional developments in the brain that mediate the relationship between psychopathology and SUD in adolescence. Externalizing disorders and SUD are both associated with structural and functional changes in the basal ganglia and prefrontal cortex in adolescence. The neural mechanisms underlying internalizing disorders and SUD are less clear, but evidence points to involvement of the amygdala and prefrontal cortex. We also highlight independent contributions of SUD, which may vary in certain ways by the substances assessed. A deeper understanding of the neural basis of the relationship between psychopathology and SUD will allow for more informed interventions in this critical developmental stage.

Adolescent Substance Use and the Brain: Behavioral, Cognitive and Neuroimaging Correlates

Adolescence is an important ontogenetic period that is characterized by behaviors such as enhanced novelty-seeking, impulsivity, and reward preference, which can give rise to an increased risk for substance use. While substance use rates in adolescence are generally on a decline, the current rates combined with emerging trends, such as increases in e-cigarette use, remain a significant public health concern. In this review, we focus on the neurobiological divergences associated with adolescent substance use, derived from a cross-sectional, retrospective, and longitudinal studies, and highlight how the use of these substances during adolescence may relate to behavioral and neuroimaging-based outcomes. Identifying and understanding the associations between adolescent substance use and changes in cognition, mental health, and future substance use risk may assist our understanding of the consequences of drug exposure during this critical window.

Nicotine Effects on White Matter Microstructure in Young Adults

OBJECTIVE

Nicotine use is widely prevalent among youth, and is associated with white matter microstructural changes as measured by diffusion tensor imaging (DTI). In adults, nicotine use is generally associated with lower fractional anisotropy (FA), but in adolescents/young adults (≤30 years), microstructure appears healthier, indicated by higher FA. This cross-sectional study examined associations between nicotine use and white matter microstructure using fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in young adults.

METHODS

Fifty-three participants (18 nicotine users [10 female]/35 controls [17 female]) ages 18-25 underwent MRI scan, neuropsychological battery, toxicology screening, and drug use interview. Nicotine group associations with FA and MD were examined in various white matter tracts. In significant tracts, AD and RD were measured. Exploratory correlations were conducted between significant tracts and verbal memory and sustained attention/working memory performance.

RESULTS

Nicotine users exhibited significantly lower FA than controls in the left anterior thalamic radiation, left inferior longitudinal fasciculus, left superior longitudinal fasciculus-temporal, and left uncinate fasciculus. In these tracts, AD and RD did not differ, nor did MD differ in any tract. White matter quality was positively correlated with sustained attention/working memory performance.

CONCLUSIONS

Cigarette smoking may disrupt white matter microstructure. These results are consistent with adult studies, but inconsistent with adolescent/young adult studies, likely due to methodological and sample age differences. Further studies should examine longitudinal effects of nicotine use on white matter microstructure in a larger sample.

Patterns of white matter microstructure in individuals at ultra-high-risk for psychosis: associations to level of functioning and clinical symptoms

BACKGROUND

Individuals at ultra-high-risk (UHR) for psychosis present with emerging symptoms and decline in functioning. Previous univariate analyses have indicated widespread white matter (WM) aberrations in multiple brain regions in UHR individuals and patients with schizophrenia. Using multivariate statistics, we investigated whole brain WM microstructure and associations between WM, clinical symptoms, and level of functioning in UHR individuals.

METHODS

Forty-five UHR individuals and 45 matched healthy controls (HCs) underwent magnetic resonance diffusion tensor imaging (DTI) at 3 Tesla. UHR individuals were assessed with the Comprehensive Assessment of At-Risk Mental States, Scale for the Assessment of Negative Symptoms, and Social and Occupational Functioning Assessment Scale. Partial least-squares correlation analysis (PLSC) was used as statistical method.

RESULTS

PLSC group comparisons revealed one significant latent variable (LV) accounting for 52% of the cross-block covariance. This LV indicated a pattern of lower fractional anisotropy (FA), axial diffusivity (AD), and mode of anisotropy (MO) concomitant with higher radial diffusivity (RD) in widespread brain regions in UHR individuals compared with HCs. Within UHR individuals, PLSC revealed five significant LVs associated with symptoms and level of functioning. The first LV accounted for 31% of the cross-block covariance and indicated a pattern where higher symptom score and lower level of functioning correlated to lower FA, AD, MO, and higher RD.

CONCLUSIONS

UHR individuals demonstrate complex brain patterns of WM abnormalities. Despite the subtle psychopathology of UHR individuals, aberrations in WM appear associated with positive and negative symptoms as well as level of functioning.

Use of Electronic Nicotine Delivery Systems Among Adolescents: Status of the Evidence and Public Health Recommendations

Although the prevalence of tobacco smoking has been declining in recent years, the use of electronic nicotine delivery systems (ENDS) such as of electronic cigarettes, vaporizers, and hookahs has been steadily rising, especially among adolescents. ENDS are not only advertised to children, but their sale via the Internet has made them easily accessible to youth. In general, children perceive ENDS as safe, or at least safer than smoking traditional combustible tobacco products; however, exposure to nicotine may have deleterious effects on the developing brain. Concern also persists that ENDS may be a "starter" drug that may lead to further tobacco, drug, and/or alcohol use. In contrast to this precautionary stance that is associated with calls for legislative oversight of ENDS marketing and sales, harm reductionists claim that the risks posed by ENDS are minor in comparison with those of combustible tobacco products and that ENDS may be used as a means of nicotine replacement for smoking cessation, despite no concrete evidence to support this assertion. Many medical and health-related organizations have produced position statements concerning ENDS use, including among adolescents. This article summarizes the advantages and disadvantages of using ENDS espoused in these position statements, especially as they relate to use among adolescents. [Pediatr Ann. 2017;46(2):e69-e77.].

The influence of comorbid oppositional defiant disorder on white matter microstructure in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) are highly comorbid disorders. ADHD has been associated with altered white matter (WM) microstructure, though the literature is inconsistent, which may be due to differences in the in- or exclusion of participants with comorbid ODD. WM abnormalities in ODD are still poorly understood, and it is unclear whether comorbid ODD in ADHD may have confounded the current ADHD literature. Diffusion Tensor Imaging (DTI) was used to compare fractional anisotropy (FA) and mean diffusivity (MD) between ADHD patients with (n = 42) and without (n = 117) comorbid ODD. All participants were between 8-25 years and groups did not differ in mean age or gender. Follow-up analyses were conducted to examine the role of antisocial behaviour (conduct problems) on FA and MD values in both groups. Comorbid ODD in ADHD was associated with lower FA in left frontotemporal WM, which appeared independent of ADHD symptoms. FA was negatively associated with antisocial behaviour in ADHD + ODD, but not in ADHD-only. Comorbid ODD is associated with WM abnormalities in individuals with ADHD, which appears to be independent of ADHD symptoms. Altered WM microstructure in comorbid ODD may play a role in inconsistencies in the current DTI literature in ADHD. Altered development of these tracts may contribute to social-emotional and cognitive problems in children with oppositional and antisocial behaviour.

Larger corpus callosum and reduced orbitofrontal cortex homotopic connectivity in codeine cough syrup-dependent male adolescents and young adults

OBJECTIVES

To characterize interhemispheric functional and anatomical connectivity and their relationships with impulsive behaviour in codeine-containing cough syrup (CCS)-dependent male adolescents and young adults.

METHODS

We compared volumes of corpus callosum (CC) and its five subregion and voxel-mirrored homotopic functional connectivity (VMHC) in 33 CCS-dependent male adolescents and young adults and 38 healthy controls, group-matched for age, education and smoking status. Barratt impulsiveness scale (BIS.11) was used to assess participant impulsive behaviour. Abnormal CC subregions and VMHC revealed by group comparison were extracted and correlated with impulsive behaviour and duration of CCS use.

RESULTS

We found selective increased mid-posterior CC volume in CCS-dependent male adolescents and young adults and detected decreased homotopic interhemispheric functional connectivity of medial orbitofrontal cortex (OFC). Moreover, impairment of VMHC was associated with the impulsive behaviour and correlated with the duration of CCS abuse in CCS-dependent male adolescents and young adults.

CONCLUSIONS

These findings reveal CC abnormalities and disruption of interhemispheric homotopic connectivity in CCS-dependent male adolescents and young adults, which provide a novel insight into the impact of interhemispheric disconnectivity on impulsive behaviour in substance addiction pathophysiology.

KEY POINTS

• CCS-dependent individuals (patients) had selective increased volumes of mid-posterior corpus callosum • Patients had attenuated interhemispheric homotopic FC (VMHC) of bilateral orbitofrontal cortex • Impairment of VMHC correlated with impulsive behaviour in patients • Impairment of VMHC correlated with the CCS duration in patients.

Circuitry of self-control and its role in reducing addiction

We discuss the idea that addictions can be treated by changing the mechanisms involved in self-control with or without regard to intention. The core clinical symptoms of addiction include an enhanced incentive for drug taking (craving), impaired self-control (impulsivity and compulsivity), negative mood, and increased stress re-activity. Symptoms related to impaired self-control involve reduced activity in control networks including anterior cingulate (ACC), adjacent prefrontal cortex (mPFC), and striatum. Behavioral training such as mindfulness meditation can increase the function of control networks and may be a promising approach for the treatment of addiction, even among those without intention to quit.

White matter development and tobacco smoking in young adults: A systematic review with recommendations for future research

BACKGROUND

Adolescence and young adulthood are critical vulnerability periods for initiation of tobacco smoking. White matter development is ongoing during this time and may be influenced by exposure to nicotine. Synthesis of findings from diffusion tensor imaging (DTI) studies of adolescent and young adult smokers may be helpful in understanding the relationship between neurodevelopment and initiation and progression of tobacco-use behaviors and in guiding further research.

METHODS

A systematic literature review was conducted to identify DTI studies comparing adolescent and young adult (mean age <30 years) smokers versus nonsmokers. A total of 5 studies meeting inclusion criteria were identified. Primary study findings are reviewed and discussed within the context of neurodevelopment and in relation to findings from adult studies. Directions for further research are also discussed.

RESULTS

All identified studies reported increases in fractional anisotropy (FA) among adolescent/young adult smokers in comparison to non-smokers. Increased FA was most frequently reported in regions of the corpus callosum (genu, body and spenium), internal capsule and superior longitudinal fasciculus.

CONCLUSIONS

Findings of increased FA among adolescent/young adult smokers are contrary to those from most adult studies and thus raise the possibility of differential effects of nicotine on white matter across the lifespan. Further research including multiple time points is needed to test this hypothesis. Other areas warranting further research include DTI studies of e-cigarette use and studies incorporating measures of pubertal stage.

Neural correlates of error monitoring in adolescents prospectively predict initiation of tobacco use

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Error-related brain activity increases during adolescence.

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Weaker response to errors predicts future initiation of tobacco use.

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Faster development of error monitoring function can be a protective factor.

Deficits in self-regulation of behavior can play an important role in the initiation of substance use and progression to regular use and dependence. One of the distinct component processes of self-regulation is error monitoring, i.e. detection of a conflict between the intended and actually executed action. Here we examined whether a neural marker of error monitoring, Error-Related Negativity (ERN), predicts future initiation of tobacco use. ERN was assessed in a prospective longitudinal sample at ages 12, 14, and 16 using a flanker task. ERN amplitude showed a significant increase with age during adolescence. Reduced ERN amplitude at ages 14 and 16, as well as slower rate of its developmental changes significantly predicted initiation of tobacco use by age 18 but not transition to regular tobacco use or initiation of marijuana and alcohol use. The present results suggest that attenuated development of the neural mechanisms of error monitoring during adolescence can increase the risk for initiation of tobacco use. The present results also suggest that the role of distinct neurocognitive component processes involved in behavioral regulation may be limited to specific stages of addiction.

Thinner Medial Temporal Cortex in Adolescents With Attention-Deficit/Hyperactivity Disorder and the Effects of Stimulants

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) has been associated with widespread changes in cortical thickness (CT). Findings have been inconsistent, however, possibly due to age differences between samples. Cortical changes have also been suggested to be reduced or to disappear with stimulant treatment. We investigated differences in CT between adolescents/young adults with and without ADHD in the largest ADHD sample to date, the NeuroIMAGE sample. Second, we investigated how such differences were related to age and stimulant treatment.

METHOD

Participants (participants with ADHD = 306; healthy controls = 184, 61% male, 8-28 years of age, mean age = 17 years) underwent structural magnetic resonance imaging. Participants and pharmacies provided detailed information regarding lifetime stimulant treatment, including cumulative intake and age of treatment initiation and cessation. Vertexwise statistics were performed in Freesurfer, modeling the main effect of diagnosis on CT and its interaction with age. Effects of stimulant treatment parameters on CT were modeled within the sample with ADHD.

RESULTS

After correction for multiple comparisons, participants with ADHD showed decreased medial temporal CT in both left (pCLUSTER = .008) and right (pCLUSTER = .038) hemispheres. These differences were present across different ages and were associated with symptoms of hyperactivity and prosocial behavior. There were no age-by-diagnosis interaction effects. None of the treatment parameters predicted CT within ADHD.

CONCLUSION

Individuals with ADHD showed thinner bilateral medial temporal cortex throughout adolescence and young adulthood compared to healthy controls. We found no association between CT and stimulant treatment. The cross-sectional design of the current study warrants cautious interpretation of the findings.