Genomic architecture of human neuroanatomical diversity

Human brain anatomy is strikingly diverse and highly inheritable: genetic factors may explain up to 80% of its variability. Prior studies have tried to detect genetic variants with a large effect on neuroanatomical diversity, but those currently identified account for <5% of the variance. Here, based on our analyses of neuroimaging and whole-genome genotyping data from 1765 subjects, we show that up to 54% of this heritability is captured by large numbers of single-nucleotide polymorphisms of small-effect spread throughout the genome, especially within genes and close regulatory regions. The genetic bases of neuroanatomical diversity appear to be relatively independent of those of body size (height), but shared with those of verbal intelligence scores. The study of this genomic architecture should help us better understand brain evolution and disease.

Resilience and corpus callosum microstructure in adolescence

BACKGROUND

Resilience is the capacity of individuals to resist mental disorders despite exposure to stress. Little is known about its neural underpinnings. The putative variation of white-matter microstructure with resilience in adolescence, a critical period for brain maturation and onset of high-prevalence mental disorders, has not been assessed by diffusion tensor imaging (DTI). Lower fractional anisotropy (FA) though, has been reported in the corpus callosum (CC), the brain's largest white-matter structure, in psychiatric and stress-related conditions. We hypothesized that higher FA in the CC would characterize stress-resilient adolescents.

METHOD

Three groups of adolescents recruited from the community were compared: resilient with low risk of mental disorder despite high exposure to lifetime stress (n = 55), at-risk of mental disorder exposed to the same level of stress (n = 68), and controls (n = 123). Personality was assessed by the NEO-Five Factor Inventory (NEO-FFI). Voxelwise statistics of DTI values in CC were obtained using tract-based spatial statistics. Regional projections were identified by probabilistic tractography.

RESULTS

Higher FA values were detected in the anterior CC of resilient compared to both non-resilient and control adolescents. FA values varied according to resilience capacity. Seed regional changes in anterior CC projected onto anterior cingulate and frontal cortex. Neuroticism and three other NEO-FFI factor scores differentiated non-resilient participants from the other two groups.

CONCLUSION

High FA was detected in resilient adolescents in an anterior CC region projecting to frontal areas subserving cognitive resources. Psychiatric risk was associated with personality characteristics. Resilience in adolescence may be related to white-matter microstructure.

Adolescent bullying, cannabis use and emerging psychotic experiences: a longitudinal general population study

BACKGROUND

Using longitudinal and prospective measures of psychotic experiences during adolescence, we assessed the risk of developing psychosis in three groups showing low, increasing and elevated psychotic experiences associated with bullying by peers and cannabis use in a UK sample of adolescents. Method Data were collected by self-report from 1098 adolescents (mean age 13.6 years; 60.9% boys) at five separate time points, equally separated by 6 months, across a 24-month period. General growth mixture modelling identified three distinct trajectories of adolescents reporting psychotic experiences: elevated, increasing and low.

RESULTS

Controlling for cannabis use, bullying by peers significantly predicted change in psychotic experiences between Time 2 and Time 5 in adolescents belonging to the increasing group. No effect was found for the elevated or low groups. Controlling for bullying, an earlier age of cannabis use and cannabis use more than twice significantly predicted change in psychotic experiences in adolescents belonging to the increasing group. Cannabis use at any age was significantly associated with subsequent change in psychotic experiences in the low group. Reverse causal associations were examined and there was no evidence for psychotic experiences at Time 1 predicting a subsequent change in cannabis use between Times 2 and 5 in any trajectory group.

CONCLUSIONS

Bullying by peers and cannabis use are associated with adolescents' reports of increasing psychotic experiences over time. Further research into the longitudinal development of psychosis in adolescence and the associated risk factors would allow for early intervention programmes to be targeted more precisely.

Maternal interpersonal affiliation is associated with adolescents' brain structure and reward processing

Considerable animal and human research has been dedicated to the effects of parenting on structural brain development, focusing on hippocampal and prefrontal areas. Conversely, although functional imaging studies suggest that the neural reward circuitry is involved in parental affection, little is known about mothers' interpersonal qualities in relation to their children's brain structure and function. Moreover, gender differences concerning the effect of maternal qualities have rarely been investigated systematically. In 63 adolescents, we assessed structural and functional magnetic resonance imaging as well as interpersonal affiliation in their mothers. This allowed us to associate maternal affiliation with gray matter density and neural responses during different phases of the well-established Monetary Incentive Delay task. Maternal affiliation was positively associated with hippocampal and orbitofrontal gray matter density. Moreover, in the feedback of reward hit as compared with reward miss, an association with caudate activation was found. Although no significant gender effects were observed in these associations, during reward feedback as compared with baseline, maternal affiliation was significantly associated with ventral striatal and caudate activation only in females. Our findings demonstrate that maternal interpersonal affiliation is related to alterations in both the brain structure and reward-related activation in healthy adolescents. Importantly, the pattern is in line with typical findings in depression and post-traumatic stress disorder, suggesting that a lack of maternal affiliation might have a role in the genesis of mental disorders.

Ethanol-induced change in cardiac and endogenous opiate function and risk for alcoholism

Susceptibility to alcoholism varies with age, gender, and familial background. Youthful nonalcoholic males with multigenerational family histories of male alcoholism seem at particular risk. Previous investigations suggest that such males are characterized by abnormal psychophysiological response, while sober and alcohol-intoxicated; additional recent studies indicate that the endogenous opiate systems are involved in mediating ethanol reinforcement and modulating intake. We first compared cardiac response to alcohol administration among young (mean = 22.8 years), nonalcoholic men and women with multigenerational, unigenerational, and negative family histories of alcohol dependence and abuse. Then, we compared the ethanol-induced cardiac response of the males in these three groups to that of currently alcohol-dependent older males and age-matched nonalcoholic male controls. Finally, we examined ethanol-induced change in plasma beta-endorphin and cortisol levels among a subset of the nonalcoholic males, divided into those with high and low levels of postethanol administration heart-rate increase. Nonalcoholic males with multigenerational family histories of male alcoholism were characterized by significantly higher [t(301) = 5.70, p < 0.0001, Cohen's d = 0.73] levels of ethanol-induced heart-rate increase than nonalcoholics from all other comparison groups. The magnitude of their increase matched that of current male alcohol-dependents. Nonalcoholic males with high levels of ethanol-induced heart-rate increase also produced significantly more plasma beta-endorphin after consuming alcohol. Peak production of beta-endorphin was highly correlated (r = 0.861, p < 0.001) with magnitude of heart-rate increase. A subset of those at risk for alcoholism may be characterized by sensitivity to ethanol-induced reward, marked by heightened ethanol-induced, heart-rate increase, mediated by ethanol stimulation of endogenous opiate production. This subset might contain those who, once alcoholic, would differentially benefit from treatment with opiate antagonists.