Sex differences in neural correlates of common psychopathological symptoms in early adolescence

BACKGROUND

Sex-related differences in psychopathology are known phenomena, with externalizing and internalizing symptoms typically more common in boys and girls, respectively. However, the neural correlates of these sex-by-psychopathology interactions are underinvestigated, particularly in adolescence.

METHODS

Participants were 14 years of age and part of the IMAGEN study, a large (N = 1526) community-based sample. To test for sex-by-psychopathology interactions in structural grey matter volume (GMV), we used whole-brain, voxel-wise neuroimaging analyses based on robust non-parametric methods. Psychopathological symptom data were derived from the Strengths and Difficulties Questionnaire (SDQ).

RESULTS

We found a sex-by-hyperactivity/inattention interaction in four brain clusters: right temporoparietal-opercular region (p < 0.01, Cohen's d = -0.24), bilateral anterior and mid-cingulum (p < 0.05, Cohen's d = -0.18), right cerebellum and fusiform (p < 0.05, Cohen's d = -0.20) and left frontal superior and middle gyri (p < 0.05, Cohen's d = -0.26). Higher symptoms of hyperactivity/inattention were associated with lower GMV in all four brain clusters in boys, and with higher GMV in the temporoparietal-opercular and cerebellar-fusiform clusters in girls.

CONCLUSIONS

Using a large, sex-balanced and community-based sample, our study lends support to the idea that externalizing symptoms of hyperactivity/inattention may be associated with different neural structures in male and female adolescents. The brain regions we report have been associated with a myriad of important cognitive functions, in particular, attention, cognitive and motor control, and timing, that are potentially relevant to understand the behavioural manifestations of hyperactive and inattentive symptoms. This study highlights the importance of considering sex in our efforts to uncover mechanisms underlying psychopathology during adolescence.

Nighttime lights, urban features, household poverty, depression, and obesity

Nighttime Light Emission (NLE) is associated with diminished mental and physical health. The present study examines how NLE and associated urban features (e.g., air pollution, low green space) impact mental and physical wellbeing. We included 200,393 UK Biobank Cohort participants with complete data. The study was carried out in two steps. In Step1, we assessed the relationship between NLE, deprivation, pollution, green space, household poverty and mental and physical symptoms. In Step2, we examined the role of NLE on environment-symptom networks. We stratified participants into high and low NLE and used gaussian graphical model to identify nodes which bridged urban features and mental and physical health problems. We then compared the global strength of these networks in high vs low NLE. We found that higher NLE associated with higher air pollution, less green space, higher economic and neighborhood deprivation, higher household poverty and higher depressed mood, higher tiredness/lethargy and obesity (Rtraining_mean = 0.2624, P training_mean < .001; Rtest_mean = 0.2619, P test_mean < .001). We also found that the interaction between environmental risk factors and mental, physical problems (overall network connectivity) was higher in the high NLE network than in the low NLE network (t = 0.7896, P < .001). In areas with high NLE, economic deprivation, household poverty and waist circumference acted as bridge factors between the key urban features and mental health symptoms. In conclusion, NLE, urban features, household poverty and mental and physical symptoms are all interrelated. In areas with high NLE, urban features associate with mental and physical health problems at a greater magnitude than in areas with low NLE.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12144-022-02754-3.

Global urbanicity is associated with brain and behaviour in young people

Urbanicity is a growing environmental challenge for mental health. Here, we investigate correlations of urbanicity with brain structure and function, neuropsychology and mental illness symptoms in young people from China and Europe (total n = 3,867). We developed a remote-sensing satellite measure (UrbanSat) to quantify population density at any point on Earth. UrbanSat estimates of urbanicity were correlated with brain volume, cortical surface area and brain network connectivity in the medial prefrontal cortex and cerebellum. UrbanSat was also associated with perspective-taking and depression symptoms, and this was mediated by neural variables. Urbanicity effects were greatest when urban exposure occurred in childhood for the cerebellum, and from childhood to adolescence for the prefrontal cortex. As UrbanSat can be generalized to different geographies, it may enable assessments of correlations of urbanicity with mental illness and resilience globally.

Do ADHD-impulsivity and BMI have shared polygenic and neural correlates?

There is an extensive body of literature linking ADHD to overweight and obesity. Research indicates that impulsivity features of ADHD account for a degree of this overlap. The neural and polygenic correlates of this association have not been thoroughly examined. In participants of the IMAGEN study, we found that impulsivity symptoms and body mass index (BMI) were associated (r = 0.10, n = 874, p = 0.014 FWE corrected), as were their respective polygenic risk scores (PRS) (r = 0.17, n = 874, p = 6.5 × 10-6 FWE corrected). We then examined whether the phenotypes of impulsivity and BMI, and the PRS scores of ADHD and BMI, shared common associations with whole-brain grey matter and the Monetary Incentive Delay fMRI task, which associates with reward-related impulsivity. A sparse partial least squared analysis (sPLS) revealed a shared neural substrate that associated with both the phenotypes and PRS scores. In a last step, we conducted a bias corrected bootstrapped mediation analysis with the neural substrate score from the sPLS as the mediator. The ADHD PRS associated with impulsivity symptoms (b = 0.006, 90% CIs = 0.001, 0.019) and BMI (b = 0.009, 90% CIs = 0.001, 0.025) via the neuroimaging substrate. The BMI PRS associated with BMI (b = 0.014, 95% CIs = 0.003, 0.033) and impulsivity symptoms (b = 0.009, 90% CIs = 0.001, 0.025) via the neuroimaging substrate. A common neural substrate may (in part) underpin shared genetic liability for ADHD and BMI and the manifestation of their (observable) phenotypic association.

Cannabis-Associated Psychotic-like Experiences Are Mediated by Developmental Changes in the Parahippocampal Gyrus

OBJECTIVE

Cannabis consumption during adolescence has been reported as a risk factor for psychotic-like experiences (PLEs) and schizophrenia. However, brain developmental processes associated with cannabis-related PLEs are still poorly described.

METHOD

A total of 706 adolescents from the general population who were recruited by the IMAGEN consortium had structural magnetic resonance imaging scans at both 14 and 19 years of age. We used deformation-based morphometry to map voxelwise brain changes between the two time points, using the pairwise algorithm in SPM12b. We used an a priori region-of-interest approach focusing on the hippocampus/parahippocampus to perform voxelwise linear regressions. Lifetime cannabis consumption was assessed using the European School Survey Project on Alcohol and other Drugs (ESPAD), and PLEs were assessed with the Comprehensive Assessment Psychotic-like experiences (CAPE) tool. We first tested whether hippocampus/parahippocampus development was associated with PLEs. Then we formulated and tested an a priori simple mediation model in which uncus development mediates the association between lifetime cannabis consumption and PLEs.

RESULTS

We found that PLEs were associated with reduced expansion within a specific region of the right hippocampus/parahippocampus formation, the uncus (p = .002 at the cluster level, p = .018 at the peak level). The partial simple mediation model revealed a significant total effect from lifetime cannabis consumption to PLEs (b = 0.069, 95% CI = 0.04-0.1, p =2 × 10^-16), as well as a small yet significant, indirect effect of right uncus development (0.004; 95% CI = 0.0004-0.01, p = .026).

CONCLUSION

We show here that the uncus development is involved in the cerebral basis of PLEs in a population-based sample of healthy adolescents.

Neurobehavioural characterisation and stratification of reinforcement-related behaviour

Reinforcement-related cognitive processes, such as reward processing, inhibitory control and social-emotional regulation are critical components of externalising and internalising behaviours. It is unclear to what extent the deficit in each of these processes contributes to individual behavioural symptoms, how their neural substrates give rise to distinct behavioural outcomes and whether neural activation profiles across different reinforcement-related processes might differentiate individual behaviours. We created a statistical framework that enabled us to directly compare functional brain activation during reward anticipation, motor inhibition and viewing emotional faces in the European IMAGEN cohort of 2,000 14-year-old adolescents. We observe significant correlations and modulation of reward anticipation and motor inhibition networks in hyperactivity, impulsivity, inattentive behaviour and conduct symptoms, and we describe neural signatures across cognitive tasks that differentiate these behaviours. We thus characterise shared and distinct functional brain activation patterns underling different externalising symptoms and identify neural stratification markers, while accounting for clinically observed comorbidity.

Association of Gray Matter and Personality Development With Increased Drunkenness Frequency During Adolescence

IMPORTANCE

Alcohol abuse correlates with gray matter development in adolescents, but the directionality of this association remains unknown.

OBJECTIVE

To investigate the directionality of the association between gray matter development and increase in frequency of drunkenness among adolescents.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study analyzed participants of IMAGEN, a multicenter brain imaging study of healthy adolescents in 8 European sites in Germany (Mannheim, Dresden, Berlin, and Hamburg), the United Kingdom (London and Nottingham), Ireland (Dublin), and France (Paris). Data from the second follow-up used in the present study were acquired from January 1, 2013, to December 31, 2016, and these data were analyzed from January 1, 2016, to March 31, 2018. Analyses were controlled for sex, site, socioeconomic status, family history of alcohol dependency, puberty score, negative life events, personality, cognition, and polygenic risk scores. Personality and frequency of drunkenness were assessed at age 14 years (baseline), 16 years (first follow-up), and 19 years (second follow-up). Structural brain imaging scans were acquired at baseline and second follow-up time points.

MAIN OUTCOMES AND MEASURES

Increases in drunkenness frequency were measured by latent growth modeling, a voxelwise hierarchical linear model was used to observe gray matter volume, and tensor-based morphometry was used for gray matter development. The hypotheses were formulated before the data analyses.

RESULTS

A total of 726 adolescents (mean [SD] age at baseline, 14.4 [0.38] years; 418 [58%] female) were included. The increase in drunkenness frequency was associated with accelerated gray matter atrophy in the left posterior temporal cortex (peak: t1,710 = -5.8; familywise error (FWE)-corrected P = 7.2 × 10-5; cluster: 6297 voxels; P = 2.7 × 10-5), right posterior temporal cortex (cluster: 2070 voxels; FWE-corrected P = .01), and left prefrontal cortex (peak: t1,710 = -5.2; FWE-corrected P = 2 × 10-3; cluster: 10 624 voxels; P = 1.9 × 10-7). According to causal bayesian network analyses, 73% of the networks showed directionality from gray matter development to drunkenness increase as confirmed by accelerated gray matter atrophy in late bingers compared with sober controls (n = 20 vs 60; β = 1.25; 95% CI, -2.15 to -0.46; t1,70 = 0.3; P = .004), the association of drunkenness increase with gray matter volume at age 14 years (β = 0.23; 95% CI, 0.01-0.46; t1,584 = 2; P = .04), the association between gray matter atrophy and alcohol drinking units (β = -0.0033; 95% CI, -6 × 10-3 to -5 × 10-4; t1,509 = -2.4; P = .02) and drunkenness frequency at age 23 years (β = -0.16; 95% CI, -0.28 to -0.03; t1,533 = -2.5; P = .01), and the linear exposure-response curve stratified by gray matter atrophy and not by increase in frequency of drunkenness.

CONCLUSIONS AND RELEVANCE

This study found that gray matter development and impulsivity were associated with increased frequency of drunkenness by sex. These results suggest that neurotoxicity-related gray matter atrophy should be interpreted with caution.

Identification of neurobehavioural symptom groups based on shared brain mechanisms

Most psychopathological disorders develop in adolescence. The biological basis for this development is poorly understood. To enhance diagnostic characterization and develop improved targeted interventions, it is critical to identify behavioural symptom groups that share neural substrates. We ran analyses to find relationships between behavioural symptoms and neuroimaging measures of brain structure and function in adolescence. We found two symptom groups, consisting of anxiety/depression and executive dysfunction symptoms, respectively, that correlated with distinct sets of brain regions and inter-regional connections, measured by structural and functional neuroimaging modalities. We found that the neural correlates of these symptom groups were present before behavioural symptoms had developed. These neural correlates showed case-control differences in corresponding psychiatric disorders, depression and attention deficit hyperactivity disorder in independent clinical samples. By characterizing behavioural symptom groups based on shared neural mechanisms, our results provide a framework for developing a classification system for psychiatric illness that is based on quantitative neurobehavioural measures.

Multi-Site Meta-Analysis of Morphometry

Genome-wide association studies (GWAS) link full genome data to a handful of traits. However, in neuroimaging studies, there is an almost unlimited number of traits that can be extracted for full image-wide big data analyses. Large populations are needed to achieve the necessary power to detect statistically significant effects, emphasizing the need to pool data across multiple studies. Neuroimaging consortia, e.g., ENIGMA and CHARGE, are now analyzing MRI data from over 30,000 individuals. Distributed processing protocols extract harmonized features at each site, and pool together only the cohort statistics using meta analysis to avoid data sharing. To date, such MRI projects have focused on single measures such as hippocampal volume, yet voxelwise analyses (e.g., tensor-based morphometry; TBM) may help better localize statistical effects. This can lead to $10^{13}$1013 tests for GWAS and become underpowered. We developed an analytical framework for multi-site TBM by performing multi-channel registration to cohort-specific templates. Our results highlight the reliability of the method and the added power over alternative options while preserving single site specificity and opening the doors for well-powered image-wide genome-wide discoveries.

White matter microstructure is associated with hyperactive/inattentive symptomatology and polygenic risk for attention-deficit/hyperactivity disorder in a population-based sample of adolescents

Few studies have investigated the link between putative biomarkers of attention-deficit/hyperactivity disorder (ADHD) symptomatology and genetic risk for ADHD. To address this, we investigate the degree to which ADHD symptomatology is associated with white matter microstructure and cerebral cortical thickness in a large population-based sample of adolescents. Critically, we then test the extent to which multimodal correlates of ADHD symptomatology are related to ADHD polygenic risk score (PRS). Neuroimaging, genetic, and behavioral data were obtained from the IMAGEN study. A dimensional ADHD composite score was derived from multi-informant ratings of ADHD symptomatology. Using tract-based spatial statistics, whole brain voxel-wise regressions between fractional anisotropy (FA) and ADHD composite score were calculated. Local cortical thickness was regressed on ADHD composite score. ADHD PRS was based on a very recent genome-wide association study, and calculated using PRSice. ADHD composite score was negatively associated with FA in several white matter pathways, including bilateral superior and inferior longitudinal fasciculi (p < 0.05, corrected). ADHD composite score was negatively associated with orbitofrontal cortical thickness (p < 0.05, corrected). The ADHD composite score was correlated with ADHD PRS (p < 0.001). FA correlates of ADHD symptomatology were significantly associated with ADHD PRS, whereas cortical thickness correlates of ADHD symptomatology were unrelated to ADHD PRS. Variation in hyperactive/inattentive symptomatology was associated with white matter microstructure, which, in turn, was related to ADHD PRS. Results suggest that genetic risk for ADHD symptomatology may be tied to biological processes affecting white matter microstructure.

Neural Correlates of Failed Inhibitory Control as an Early Marker of Disordered Eating in Adolescents

BACKGROUND

Binge eating and other forms of disordered eating behavior (DEB) are associated with failed inhibitory control. This study investigated the neural correlates of failed inhibitory control as a potential biomarker for DEB.

METHODS

The study used prospective longitudinal data from the European IMAGEN study adolescent cohort. Participants completed baseline assessments (questionnaires and a brain scan [functional magnetic resonance imaging]) at 14 years of age and a follow-up assessment (questionnaires) at 16 years of age. Self-reported binge eating and/or purging were used to indicate presence of DEB. Neural correlates of failed inhibition were assessed using the stop signal task. Participants were categorized as healthy control subjects (reported no DEB at both time points), maintainers (reported DEB at both time points), recoverers (reported DEB at baseline only), and developers (reported DEB at follow-up only). Forty-three individuals per group with complete scanning data were matched on gender, age, puberty, and intelligence (N = 172).

RESULTS

At baseline, despite similar task performance, incorrectly responding to stop signals (failed inhibitory control) was associated with greater recruitment of the medial prefrontal cortex and anterior cingulate cortex in the developers compared with healthy control subjects and recoverers.

CONCLUSIONS

Greater recruitment of the medial prefrontal and anterior cingulate regions during failed inhibition accords with abnormal evaluation of errors contributing to DEB development. As this precedes symptom onset and is evident despite normal task performance, neural responses during failed inhibition may be a useful biomarker of vulnerability for DEB. This study highlights the potential value of prospective neuroimaging studies for identifying markers of illness before the emergence of behavior changes.

Allele-Specific Methylation of SPDEF: A Novel Moderator of Psychosocial Stress and Substance Abuse

OBJECTIVE

Psychosocial stress is a key risk factor for substance abuse among adolescents. Recently, epigenetic processes such as DNA methylation have emerged as potential mechanisms that could mediate this relationship. The authors conducted a genome-wide methylation analysis to investigate whether differentially methylated regions are associated with psychosocial stress in an adolescent population.

METHODS

A methylome-wide analysis of differentially methylated regions was used to examine a sample of 1,287 14-year-old adolescents (50.7% of them female) from the European IMAGEN study. The Illumina 450k array was used to assess DNA methylation, pyrosequencing was used for technical replication, and linear regression analyses were used to identify associations with psychosocial stress and substance use (alcohol and tobacco). Findings were replicated by pyrosequencing a test sample of 413 participants from the IMAGEN study.

RESULTS

Hypermethylation in the sterile alpha motif/pointed domain containing the ETS transcription factor (SPDEF) gene locus was associated with a greater number of stressful life events in an allele-dependent way. Among individuals with the minor G-allele, SPDEF methylation moderated the association between psychosocial stress and substance abuse. SPDEF methylation interacted with lifetime stress in gray matter volume in the right cuneus, which in turn was associated with the frequency of alcohol and tobacco use. SPDEF was involved in the regulation of trans-genes linked to substance use.

CONCLUSIONS

Taken together, the study findings describe a novel epigenetic mechanism that helps explain how psychosocial stress exposure influences adolescent substance abuse.

Behavioral and Health Correlates of Resting-State Metastability in the Human Connectome Project

Metastability is currently considered a fundamental property of the functional configuration of brain networks. The present study sought to generate a normative reference framework for the metastability of the major resting-state networks (RSNs) (resting-state metastability dataset) and discover their association with demographic, behavioral, physical and cognitive features (non-imaging dataset) from 818 participants of the Human Connectome Project. Using sparse canonical correlation analysis, we found that the metastability and non-imaging datasets showed significant but modest interdependency. Notable associations between the metastability variate and the non-imaging features were observed for higher-order cognitive ability and indicators of physical well-being. The intra-class correlation coefficient between the sibling pairs in the sample was very low which argues against a significant familial influence on RSN metastability.

Multivariate Associations Among Behavioral, Clinical, and Multimodal Imaging Phenotypes in Patients With Psychosis

IMPORTANCE

Alterations in multiple neuroimaging phenotypes have been reported in psychotic disorders. However, neuroimaging measures can be influenced by factors that are not directly related to psychosis and may confound the interpretation of case-control differences. Therefore, a detailed characterization of the contribution of these factors to neuroimaging phenotypes in psychosis is warranted.

OBJECTIVE

To quantify the association between neuroimaging measures and behavioral, health, and demographic variables in psychosis using an integrated multivariate approach.

DESIGN, SETTING, AND PARTICIPANTS

This imaging study was conducted at a university research hospital from June 26, 2014, to March 9, 2017. High-resolution multimodal magnetic resonance imaging data were obtained from 100 patients with schizophrenia, 40 patients with bipolar disorder, and 50 healthy volunteers; computed were cortical thickness, subcortical volumes, white matter fractional anisotropy, task-related brain activation (during working memory and emotional recognition), and resting-state functional connectivity. Ascertained in all participants were nonimaging measures pertaining to clinical features, cognition, substance use, psychological trauma, physical activity, and body mass index. The association between imaging and nonimaging measures was modeled using sparse canonical correlation analysis with robust reliability testing.

MAIN OUTCOMES AND MEASURES

Multivariate patterns of the association between nonimaging and neuroimaging measures in patients with psychosis and healthy volunteers.

RESULTS

The analyses were performed in 92 patients with schizophrenia (23 female [25.0%]; mean [SD] age, 27.0 [7.6] years), 37 patients with bipolar disorder (12 female [32.4%]; mean [SD] age, 27.5 [8.1] years), and 48 healthy volunteers (20 female [41.7%]; mean [SD] age, 29.8 [8.5] years). The imaging and nonimaging data sets showed significant covariation (r = 0.63, P < .001), which was independent of diagnosis. Among the nonimaging variables examined, age (r = -0.53), IQ (r = 0.36), and body mass index (r = -0.25) were associated with multiple imaging phenotypes; cannabis use (r = 0.23) and other substance use (r = 0.33) were associated with subcortical volumes, and alcohol use was associated with white matter integrity (r = -0.15). Within the multivariate models, positive symptoms retained associations with the global neuroimaging (r = -0.13), the cortical thickness (r = -0.22), and the task-related activation variates (r = -0.18); negative symptoms were mostly associated with measures of subcortical volume (r = 0.23), and depression/anxiety was associated with measures of white matter integrity (r = 0.12).

CONCLUSIONS AND RELEVANCE

Multivariate analyses provide a more accurate characterization of the association between brain alterations and psychosis because they enable the modeling of other key factors that influence neuroimaging phenotypes.

Does Bowel Preparation for Colonoscopy Affect Cognitive Function?

Colonoscopy is a common procedure used in the diagnosis and treatment of a range of bowel disorders. Prior preparation involving potent laxatives is a necessary stage to ensure adequate visualization of the bowel wall. It is known that the sedatives given to most patients during the colonoscopy cause a temporary impairment in cognitive function; however, the potential for bowel preparation to affect cognitive function has not previously been investigated. To assess the effect of bowel preparation for colonoscopy on cognitive function. This was a prospective, nonrandomized controlled study of cognitive function in patients who had bowel preparation for colonoscopy compared with those having gastroscopy and therefore no bowel preparation. Cognitive function was assessed using the Modified Mini Mental State Examination (MMMSE) and selected tests from the Cambridge Neuropsychological Test Automated Battery. Individual test scores and changes between initial and subsequent tests were compared between the groups. Age, gender, and weight were also compared. Forty-three colonoscopy and 25 gastroscopy patients were recruited. The 2 groups were similar for age and gender; however, patients having gastroscopy were heavier. MMMSE scores for colonoscopy and gastroscopy groups, respectively, were 28.6 and 29.5 (P = 0.24) at baseline, 28.7 and 29.8 (P = 0.32) at test 2, 28.1 and 28.5 (P = 0.76) at test 3. Motor screening scores for colonoscopy and gastroscopy groups, respectively, were 349.3 and 354.1 (P = 0.97) at baseline, 307.5 and 199.7 (P = 0.06) at test 2, 212.0 and 183.2 (P = 0.33) at test 3. Spatial working memory scores for colonoscopy and gastroscopy groups, respectively, were 14.4 and 6.7 (P = 0.29) at baseline, 9.7 and 4.3 (P = 0.27) at test 2, 10 and 4.5 (P = 0.33) at test 3. Digit Symbol Substitution Test scores for colonoscopy and gastroscopy groups, respectively, were 36.3 and 37.8 (P = 0.84) at baseline, 36.4 and 40.0 (P = 0.59) at test 2, 38.6 and 40.8 (P = 0.76) at test 3.This study did not find evidence of cognitive impairment resulting from administration of bowel preparation before colonoscopy.

Cluster size statistic and cluster mass statistic: two novel methods for identifying changes in functional connectivity between groups or conditions

Functional connectivity has become an increasingly important area of research in recent years. At a typical spatial resolution, approximately 300 million connections link each voxel in the brain with every other. This pattern of connectivity is known as the functional connectome. Connectivity is often compared between experimental groups and conditions. Standard methods used to control the type 1 error rate are likely to be insensitive when comparisons are carried out across the whole connectome, due to the huge number of statistical tests involved. To address this problem, two new cluster based methods--the cluster size statistic (CSS) and cluster mass statistic (CMS)--are introduced to control the family wise error rate across all connectivity values. These methods operate within a statistical framework similar to the cluster based methods used in conventional task based fMRI. Both methods are data driven, permutation based and require minimal statistical assumptions. Here, the performance of each procedure is evaluated in a receiver operator characteristic (ROC) analysis, utilising a simulated dataset. The relative sensitivity of each method is also tested on real data: BOLD (blood oxygen level dependent) fMRI scans were carried out on twelve subjects under normal conditions and during the hypercapnic state (induced through the inhalation of 6% CO2 in 21% O2 and 73%N2). Both CSS and CMS detected significant changes in connectivity between normal and hypercapnic states. A family wise error correction carried out at the individual connection level exhibited no significant changes in connectivity.

The impact of latent confounders in directed network analysis in neuroscience

In the analysis of neuroscience data, the identification of task-related causal relationships between various areas of the brain gives insights about the network of physiological pathways that are active during the task. One increasingly used approach to identify causal connectivity uses the concept of Granger causality that exploits predictability of activity in one region by past activity in other regions of the brain. Owing to the complexity of the data, selecting components for the analysis of causality as a preprocessing step has to be performed. This includes predetermined-and often arbitrary-exclusion of information. Therefore, the system is confounded by latent sources. In this paper, the effect of latent confounders is demonstrated, and paths of influence among three components are studied. While methods for analysing Granger causality are commonly based on linear vector autoregressive models, the effects of latent confounders are expected to be present also in nonlinear systems. Therefore, all analyses are also performed for a simulated nonlinear system and discussed with regard to applications in neuroscience.

A dual echo approach to motion correction for functional connectivity studies

The effect of subject head movement on functional connectivity as measured by BOLD (blood oxygen level dependent) fMRI was investigated; movement mainly introduced increases in connectivity into the dataset. The effect of movement on connectivity is an important consideration when comparing patients suffering from neurological conditions to healthy controls, since it is well known that patients affected by such conditions are prone to move more in the scanner than healthy subjects. A method of motion correction utilising a dual echo EPI sequence is described. The first echo is acquired soon after the slice excitation (TE(1)=10 ms) when BOLD contrast is low and the MR signal is mainly sensitive to movement related effects, while the second echo is acquired at an echo time (TE(2)=30 ms) at which the MR signal is sensitive to both BOLD and movement related effects. To correct for additional signal variance introduced by subject movement, the second echo image is divided by the first echo image at each time point across the length of the scan. This procedure is easy to implement and requires no extra scan time. This method proved superior to the standard means of correction whereby realignment parameters and their first order derivatives are used as covariates of no interest in a linear regression model.

University students' notebook computer use: lessons learned using e-diaries to report musculoskeletal discomfort

The objective of this pilot study was to identify if notebook accessories (ergonomic chair, desktop monitor and notebook riser) combined with a wireless keyboard, mouse and participatory ergonomics training would have the greatest impact on reducing self-reported upper extremity musculoskeletal discomfort in university students. In addition to pre-post computing and health surveys, the Ecological Momentary Assessment was used to capture change in discomfort over time using a personal digital assistant (PDA) as the e-diary. The PDA was programmed with a survey containing 45 questions. Four groups of university students were randomised to either intervention (three external computer accessories) or to control. Participants reported less discomfort with the ergonomic chair and notebook riser based on the pre-post survey data and the e-diary/PDA ANOVA analysis. However, the PDA data, adjusted for the effect of hours per day of computer use, showed no benefit of the chair and limited benefit from the riser. Statement of Relevance:University students' use of notebook computers has increased. This study found evidence of a positive effect of an adjustable chair or notebook riser when combined with ergonomic training on reducing discomfort. Daily notebook computer use of 4 h was confirmed as a risk factor. Without some form of ergonomic intervention, these students are likely to enter the workforce with poor computing habits, which places them on the road to future injuries as technology continues to play a dominant role in their lives.

Immunomodulation does not alter histology in resected Crohn's disease

BACKGROUND

The use of immunomodulators (Azathioprine, 6-Mercaptopurine and Methotrexate) and biological agents (Infliximab and adalimumab) for the treatment of Crohn's disease (CD) has increased in the recent years with the aim of treating the inflammatory component of the disease and hoping to change the natural history of the disease. The aim of this study was to determine if the use of immunomodulators or biological agents in the 2 years prior to resection affects the histopathological characteristics of the patient's disease.

METHODS

A retrospective review was conducted over a 10-year period (1996-2005) of patients who underwent resection for CD. Clinical case notes and histology specimens were reviewed. Patients treated with Azathioprine, 6-Mercaptopurine, Methotrexate or Infliximab for more than 3 months within the 2 years preceding surgery were deemed to have been immunomodulated. The results were also analysed by Montreal phenotype.

RESULTS

A total of 165 patients were identified. 52 patients had been treated with either immunomodulator or biological agent. Of 20 histological features examined, only muscular hypertrophy approached significance (P = 0.05), Montreal A and Montreal L phenotypes were the same regardless on immunomodulators, however, there was a significant difference (P = 0.03) with regard to Montreal B in patients with stricturing disease being more likely to have received an immunomodulator.

CONCLUSIONS

In this cohort of patients requiring resection for CD, those with stricturing disease were more likely to receive immunomodulators or biologics than those without stricturing disease. However, there were no significant histological differences in the resected specimens between those who did and those who did not receive these drugs.

A database for environmental contaminants in traditional food in northern Canada

The potential health effects of environmental contaminants in traditional food on indigenous peoples in Northern Canada have been a growing concern. We have conducted an extensive literature review on contaminant levels in Northern Canada through searches of commercial, private, and government databases for the years 1986-1995, including MEDLine, Agricola, Biological Abstracts, Current Contents, Applied Science and Technology, Biosis, CABCD, Aquatic Sciences and Fisheries Abstracts, CRIS/ICAR, and the Northern Aquatic Food Chain Contaminant Database. More than 20,000 data items were identified in over 50 published articles, unpublished data, government reports, and review articles. Ranges of levels of 13 contaminants in major traditional food groups collected from four geographical regions (Yukon, MacKenzie, Keewatin, Baffin and Northern Quebec) were calculated. Exposure levels, particularly according to different dietary patterns, were estimated and discussed in relation to guideline levels.

Consumption of freshwater fish in Kahnawake: risks and benefits

Kahnawake is a Mohawk community located on the south shore of the Saint Lawrence River near Montreal. A comprehensive study was conducted in 1996-1997 to address the local concern regarding health risks of contaminant exposure associated with freshwater fish consumption. Forty-two participants, including most of the identified active fishermen (n=33), were interviewed. Walleye, perch, bullhead, and smallmouth bass were the species most consumed. Average daily intake of locally caught fish was 23 g/day. Nutrient and contaminant levels of locally collected fish were analyzed. Fish were good sources of protein, polyunsaturated fatty acids (particularly omega-3 fatty acids), calcium, zinc, and iron. Levels of cadmium, lead, arsenic, polychlorinated biphenyls (PCBs), and other chlorinated pesticides were at least 10 times lower than the guideline levels. Mercury levels of some predatory fish exceeded the guideline of 0.5 microgram/g. Average daily intakes of all contaminants were below the guideline levels by a factor of 10 except for mercury. Average mercury intake rate was about one-third that of the guideline level (200 micrograms/week). Contrary to residents' perception, Kahnawake fish were not particularly contaminated. In view of the nutritional as well as cultural benefits, fishing and fish consumption may be promoted.

Identification of alpha-cardiac myosin heavy chain mRNA and protein in extraocular muscle of the adult rabbit

Extraocular muscles contain both fast-twitch and multiply-innervated, tonic-contracting fibres. In rat, these fibres collectively express numerous myosin heavy chain isoforms including fast-type embryonic and neonatal, adult slow twitch type I and fast twitch type II, and a fast isoform unique to extraocular muscle. Immunocytochemical and Western blotting results are presented which suggest that, in rabbit, an additional species, the alpha-cardiac myosin heavy chain, is present. The immunoreactive species is found in all rabbit extraocular muscles and in the extraocular muscles is expressed in almost all fibres which do not contain a fast myosin heavy chain. Positive identification of this isoform as the alpha-cardiac myosin heavy chain was obtained by sequencing a cloned PCR product derived from extraocular muscle mRNA unique to the 3'-end of rabbit alpha-cardiac myosin heavy chain mRNA. This is the first unequivocal demonstration of alpha-cardiac myosin heavy chain expression in extraocular muscle.

Mucociliary function, ciliary ultrastructure, and ciliary orientation in Young's syndrome

BACKGROUND

Mucociliary clearance is impaired in patients with Young's syndrome (obstructive azoospermia with recurrent sinobronchial disease), cystic fibrosis, and primary ciliary dyskinesia. No defect of cilia or mucus has been detected in Young's syndrome.

METHODS

Ciliary function and ultrastructure, including ciliary orientation, were studied quantitatively in 20 patients with Young's syndrome and 20 normal subjects to determine the incidences of ciliary defects. Nasal ciliated epithelium was obtained from each subject and used for measurement of ciliary beat frequency and ultrastructural analyses. Ciliary orientation was determined by measuring ciliary deviation in electron micrographs; ciliary deviation is a measure of the relative orientation of cilia in relation to each other in which high values indicate ciliary disorientation.

RESULTS

Ciliary beat frequency and the incidence of microtubular defects and numbers of dynein arms did not differ between patients with Young's syndrome and control subjects. In patients with Young's syndrome basal ciliary deviation (16.0 degrees) was similar to that in control subjects (14.1 degrees), but at the ciliary tip ciliary deviation (21.9 degrees) was greater than in healthy subjects (14.5 degrees).

CONCLUSION

The relative disorientation of the distal ciliary axoneme in patients with Young's syndrome compared with normal subjects may be due to a structural defect but is more likely to be a consequence of abnormal mucus.

Liver blood flow after major hepatic resection

The factors involved in liver regeneration are poorly understood, but it has been suggested that blood flow plays a role. This paper documents the changes in liver blood flow (LBF) that occur after major hepatic resection. Eight patients, ranging in age from 37 to 76 years, underwent liver resection. Liver blood flow was measured preoperatively and on days 1, 4 and 7 postoperatively by low-dose galactose clearance. There was a significant (p less than 0.01) fall in LBF on day 1 compared with the baseline value, followed by a significant (p less than 0.01) rise from the baseline value by day 4. By day 7, LBF had returned to baseline levels and was significantly (p less than 0.01) lower than on day 4. These changes in LBF may be related to the stimulus for liver regeneration and increased functional demands during the early regenerative phase.

Dysfunction of humoral immunity in anergic surgical patients: absence of anti-tetanus IgG antibody production

The experiments described have shown that, whereas the injection of tetanus toxoid (tet) into 8 of 12 control individuals resulted in the appearance of specific anti-tet-IgG antibodies in their plasma, immunization of 14 anergic patients did not elicit an antibody response. This observation was extended to an in vitro system, where cells from four control subjects were shown to secrete anti-tet-IgG antibodies in response to polyclonal activators whereas cells from eight anergic patients did not. It is suggested that this failure of humoral immunity could account for the high risk of bacterial infections in anergy.