Brain reward function in people who use cannabis: a systematic review

Rationale

Cannabis is one of the most widely used psychoactive substances globally. Cannabis use can be associated with alterations of reward processing, including affective flattening, apathy, anhedonia, and lower sensitivity to natural rewards in conjunction with higher sensitivity to cannabis-related rewards. Such alterations have been posited to be driven by changes in underlying brain reward pathways, as per prominent neuroscientific theories of addiction. Functional neuroimaging (fMRI) studies have examined brain reward function in cannabis users via the monetary incentive delay (MID) fMRI task; however, this evidence is yet to be systematically synthesised.

Objectives

We aimed to systematically integrate the evidence on brain reward function in cannabis users examined by the MID fMRI task; and in relation to metrics of cannabis exposure (e.g., dosage, frequency) and other behavioural variables.

Method

We pre-registered the review in PROSPERO and reported it using PRISMA guidelines. Literature searches were conducted in PsycINFO, PubMed, Medline, CINAHL, and Scopus.

Results

Nine studies were included, comprising 534 people with mean ages 16-to-28 years, of which 255 were people who use cannabis daily or almost daily, and 279 were controls. The fMRI literature to date led to largely non-significant group differences. A few studies reported group differences in the ventral striatum while participants anticipated rewards and losses; and in the caudate while participants received neutral outcomes. A few studies examined correlations between brain function and withdrawal, dosage, and age of onset; and reported inconsistent findings.

Conclusions

There is emerging but inconsistent evidence of altered brain reward function in cannabis users examined with the MID fMRI task. Future fMRI studies are required to confirm if the brain reward system is altered in vulnerable cannabis users who experience a Cannabis Use Disorder, as postulated by prominent neuroscientific theories of addiction.

Prediction of cognitive outcome after mild traumatic brain injury from acute measures of communication within brain networks

A considerable but ill-defined proportion of patients with mild traumatic brain injury (mTBI) experience persistent cognitive sequelae; the ability to identify such individuals early can help their neurorehabilitation. Here we tested the hypothesis that acute measures of efficient communication within brain networks are associated with patients' risk for unfavorable cognitive outcome six months after mTBI. Diffusion and T1-weighted magnetic resonance imaging, alongside cognitive measures, were obtained to map connectomes both one week and six months post injury in 113 adult patients with mTBI (71 males). For task-related brain networks, communication measures (characteristic path length, global efficiency, navigation efficiency) were moderately correlated with changes in cognition. Taking into account the covariance of age and sex, more unfavorable communication within networks were associated with worse outcomes within cognitive domains frequently impacted by mTBI (episodic and working memory, verbal fluency, inductive reasoning, and processing speed). Individuals with more unfavorable outcomes had significantly longer and less efficient pathways within networks supporting verbal fluency (all t > 2.786, p < .006), highlighting the vulnerability of language to mTBI. Participants in whom a task-related network was relatively inefficient one week post injury were up to eight times more likely to have unfavorable cognitive outcome pertaining to that task. Our findings suggest that communication measures within task-related networks identify mTBI patients who are unlikely to develop persistent cognitive deficits after mTBI. Our approach and findings can help to stratify mTBI patients according to their expected need for follow-up and/or neurorehabilitation.

Characteristics of urban neighbourhood environments and cognitive age in mid-age and older adults

In this cross-sectional study, we examined the extent to which features of the neighbourhood natural, built, and socio-economic environments were related to cognitive age in adults (N = 3418, Mage = 61 years) in Australia. Machine learning estimated an individual's cognitive age from assessments of processing speed, verbal memory, premorbid intelligence. A 'cognitive age gap' was calculated by subtracting chronological age from predicted cognitive age and was used as a marker of cognitive age. Greater parkland availability and higher neighbourhood socio-economic status were associated with a lower cognitive age gap score in confounder- and mediator-adjusted regression models. Cross-sectional design is a limitation. Living in affluent neighbourhoods with access to parks maybe beneficial for cognitive health, although selection mechanisms may contribute to the findings.

Selective perforant-pathway atrophy in Huntington disease: MRI analysis of hippocampal subfields

INTRODUCTION

While individuals with Huntington disease (HD) show memory impairment that indicates hippocampal dysfunction, the available literature does not consistently identify structural evidence for involvement of the whole hippocampus but rather suggests that hippocampal atrophy may be confined to certain hippocampal subregions.

METHODS

We processed T1-weighted MRI from IMAGE-HD study using FreeSurfer 7.0 and compared the volumes of the hippocampal subfields among 36 early motor symptomatic (symp-HD), 40 pre-symptomatic (pre-HD), and 36 healthy control individuals across three timepoints over 36 months.

RESULTS

Mixed-model analyses revealed significantly lower subfield volumes in symp-HD, compared with pre-HD and control groups, in the subicular regions of the perforant-pathway: presubiculum, subiculum, dentate gyrus, tail, and right molecular layer. These adjoining subfields aggregated into a single principal component, which demonstrated an accelerated rate of atrophy in the symp-HD. Volumes between pre-HD and controls did not show any significant difference. In the combined HD groups, CAG repeat length and disease burden score were associated with presubiculum, molecular layer, tail, and perforant-pathway subfield volumes. Hippocampal left tail and perforant-pathway subfields were associated with motor onset in the pre-HD group.

CONCLUSIONS

Hippocampal subfields atrophy in early symptomatic HD affects key regions of the perforant-pathway, which may implicate the distinctive memory impairment at this stage of illness. Their volumetric associations with genetic and clinical markers suggest the selective susceptibility of these subfields to mutant Huntingtin and disease progression.

Structural-functional connectivity bandwidth predicts processing speed in mild traumatic brain Injury: A multiplex network analysis

An emerging body of work has revealed alterations in structural (SC) and functional (FC) brain connectivity following mild TBI (mTBI), with mixed findings. However, these studies seldom integrate complimentary neuroimaging modalities within a unified framework. Multilayer network analysis is an emerging technique to uncover how white matter organization enables functional communication. Using our novel graph metric (SC-FC Bandwidth), we quantified the information capacity of synchronous brain regions in 53 mild TBI patients (46 females; age mean = 40.2 years (y), σ = 16.7 (y), range: 18-79 (y). Diffusion MRI and resting state fMRI were administered at the acute and chronic post-injury intervals. Moreover, participants completed a cognitive task to measure processing speed (30 Seconds and Counting Task; 30-SACT). Processing speed was significantly increased at the chronic, relative to the acute post-injury intervals (p = <0.001). Nonlinear principal components of direct (t = -1.84, p = 0.06) and indirect SC-FC Bandwidth (t = 3.86, p = <0.001) predicted processing speed with a moderate effect size (R2 = 0.43, p < 0.001), while controlling for age. A subnetwork of interhemispheric edges with increased SC-FC Bandwidth was identified at the chronic, relative to the acute mTBI post-injury interval (pFDR = 0.05). Increased interhemispheric SC-FC Bandwidth of this network corresponded with improved processing speed at the chronic post-injury interval (partial r = 0.32, p = 0.02). Our findings revealed that mild TBI results in complex reorganization of brain connectivity optimized for maximum information flow, supporting improved cognitive performance as a compensatory mechanism. Moving forward, this measurement may complement clinical assessment as an objective marker of mTBI recovery.

Individualised profiling of white matter organisation in moderate-to-severe traumatic brain injury patients

BACKGROUND AND PURPOSE

Approximately 65% of moderate-to-severe traumatic brain injury (m-sTBI) patients present with poor long-term behavioural outcomes, which can significantly impair activities of daily living. Numerous diffusion-weighted MRI studies have linked these poor outcomes to decreased white matter integrity of several commissural tracts, association fibres and projection fibres in the brain. However, most studies have focused on group-based analyses, which are unable to deal with the substantial between-patient heterogeneity in m-sTBI. As a result, there is increasing interest and need in conducting individualised neuroimaging analyses.

MATERIALS AND METHODS

Here, we generated a detailed subject-specific characterisation of microstructural organisation of white matter tracts in 5 chronic patients with m-sTBI (29 - 49y, 2 females), presented as a proof-of-concept. We developed an imaging analysis framework using fixel-based analysis and TractLearn to determine whether the values of fibre density of white matter tracts at the individual patient level deviate from the healthy control group (n = 12, 8F, M_age = 35.7y, age range 25 - 64y).

RESULTS

Our individualised analysis revealed unique white matter profiles, confirming the heterogenous nature of m-sTBI and the need of individualised profiles to properly characterise the extent of injury. Future studies incorporating clinical data, as well as utilising larger reference samples and examining the test-retest reliability of the fixel-wise metrics are warranted.

CONCLUSIONS

Individualised profiles may assist clinicians in tracking recovery and planning personalised training programs for chronic m-sTBI patients, which is necessary to achieve optimal behavioural outcomes and improved quality of life.

Molecular characterization stratifies VQ myeloma cells into two clusters with distinct risk signatures and drug responses

Multiple myeloma (MM) is a cancer of malignant plasma cells in the bone marrow and extramedullary sites. We previously characterized a VQ model for human high-risk MM. The various VQ lines display different disease phenotypes and survival rates, suggesting significant intra-model variation. Here, we use whole-exome sequencing and copy number variation (CNV) analysis coupled with RNA-Seq to stratify the VQ lines into corresponding clusters: Group A cells had monosomy chromosome (chr) 5 and overexpressed genes and pathways associated with sensitivity to bortezomib (Btz) treatment in human MM patients. By contrast, Group B VQ cells carried recurrent amplification (Amp) of chr3 and displayed high-risk MM features, including downregulation of Fam46c, upregulation of cancer growth pathways associated with functional high-risk MM, and expression of Amp1q and high-risk UAMS-70 and EMC-92 gene signatures. Consistently, in sharp contrast to Group A VQ cells that showed short-term response to Btz, Group B VQ cells were de novo resistant to Btz in vivo. Our study highlights Group B VQ lines as highly representative of the human MM subset with ultrahigh risk.

Do neighbourhood traffic-related air pollution and socio-economic status moderate the associations of the neighbourhood physical environment with cognitive function? Findings from the AusDiab study

Characteristics of the neighbourhood environment, including the built and natural environment, area-level socio-economic status (SES) and air pollution, have been linked to cognitive health. However, most studies have focused on single neighbourhood characteristics and have not considered the extent to which the effects of environmental factors may interact. We examined the associations of measures of the neighbourhood built and natural environment, area-level SES and traffic-related air pollution (TRAP) with two cognitive function domains (memory and processing speed), and the extent to which area-level SES and TRAP moderated the associations. We used cross-sectional data from the AusDiab3 study, an Australian cohort study of adults (mean age: 61 years) in 2011-12 (N = 4141) for which geocoded residential addresses were available. Spatial data were used to create composite indices of built environment complexity (population density, intersection density, non-commercial land use mix, commercial land use) and natural environment (parkland and blue spaces). Area-level SES was obtained from national census indices and TRAP was based on estimates of annual average levels of nitrogen dioxide (NO2). Confounder-adjusted generalised additive mixed models were used to estimate the independent associations of the environmental measures with cognitive function and the moderating effects of area-level SES and TRAP. The positive associations between built environment complexity and memory were stronger in those living in areas with higher SES and lower NO2 concentrations. A positive association between the natural environment and memory was found only in those living in areas with lower NO2 concentrations and average or below-average SES. Built environment complexity and the natural environment were positively related to processing speed. Complex urban environments and access to nature may benefit cognitive health in ageing populations. For higher-order cognitive abilities, such as memory, these positive effects may be stronger in areas with lower levels of TRAP.

Exploring personalized structural connectomics for moderate to severe traumatic brain injury

Graph theoretical analysis of the structural connectome has been employed successfully to characterize brain network alterations in patients with traumatic brain injury (TBI). However, heterogeneity in neuropathology is a well-known issue in the TBI population, such that group comparisons of patients against controls are confounded by within-group variability. Recently, novel single-subject profiling approaches have been developed to capture inter-patient heterogeneity. We present a personalized connectomics approach that examines structural brain alterations in five chronic patients with moderate to severe TBI who underwent anatomical and diffusion magnetic resonance imaging. We generated individualized profiles of lesion characteristics and network measures (including personalized graph metric GraphMe plots, and nodal and edge-based brain network alterations) and compared them against healthy reference cases (N = 12) to assess brain damage qualitatively and quantitatively at the individual level. Our findings revealed alterations of brain networks with high variability between patients. With validation and comparison to stratified, normative healthy control comparison cohorts, this approach could be used by clinicians to formulate a neuroscience-guided integrative rehabilitation program for TBI patients, and for designing personalized rehabilitation protocols based on their unique lesion load and connectome.

Structural-Functional Connectivity Bandwidth of the Human Brain

BACKGROUND

The human brain is a complex network that seamlessly manifests behaviour and cognition. This network comprises neurons that directly, or indirectly mediate communication between brain regions. Here, we show how multilayer/multiplex network analysis provides a suitable framework to uncover the throughput of structural connectivity (SC) to mediate information transfer-giving rise to functional connectivity (FC).

METHOD

We implemented a novel method to reconcile SC and FC using diffusion and resting-state functional MRI connectivity data from 484 subjects (272 females, 212 males; age = 29.15 ± 3.47) from the Human Connectome Project. First, we counted the number of direct and indirect structural paths that mediate FC. FC nodes with indirect SC paths were then weighted according to their least restrictive SC path. We refer to this as SC-FC Bandwidth. We then mapped paths with the highest SC-FC Bandwidth across 7 canonical resting-state networks.

FINDINGS

We found that most pairs of FC nodes were connected by SC paths of length two and three (SC paths of length >5 were virtually non-existent). Direct SC-FC connections accounted for only 10% of all SC-FC connections. The majority of FC nodes without a direct SC path were mediated by a proportion of two (44%) or three SC path lengths (39%). Only a small proportion of FC nodes were mediated by SC path lengths of four (5%). We found high-bandwidth direct SC-FC connections show dense intra- and sparse inter-network connectivity, with a bilateral, anteroposterior distribution. High bandwidth SC-FC triangles have a right superomedial distribution within the somatomotor network. High-bandwidth SC-FC quads have a superoposterior distribution within the default mode network.

CONCLUSION

Our method allows the measurement of indirect SC-FC using undirected, weighted graphs derived from multimodal MRI data in order to map the location and throughput of SC to mediate FC. An extension of this work may be to explore how SC-FC Bandwidth changes over time, relates to cognition/behavior, and if this measure reflects a marker of neurological injury or psychiatric disorders.

Mechanisms of Resistance and Implications for Treatment Strategies in Chronic Myeloid Leukaemia

Simple Summary

Chronic myeloid leukaemia (CML) is a type of blood cancer that is currently well-managed with drugs that target cancer-causing proteins. However, a significant proportion of CML patients do not respond to those drug treatments or relapse when they stop those drugs because the cancer cells in those patients stop relying on that protein and instead develop a new way to survive. Therefore, new treatment strategies may be necessary for those patients. In this review, we discuss those additional survival pathways and outline combination treatment strategies to increase responses and clinical outcomes, improving the lives of CML patients.

Abstract

Tyrosine kinase inhibitors (TKIs) have revolutionised the management of chronic myeloid leukaemia (CML), with the disease now having a five-year survival rate over 80%. The primary focus in the treatment of CML has been on improving the specificity and potency of TKIs to inhibit the activation of the BCR::ABL1 kinase and/or overcoming resistance driven by mutations in the BCR::ABL1 oncogene. However, this approach may be limited in a significant proportion of patients who develop TKI resistance despite the effective inhibition of BCR::ABL1. These patients may require novel therapeutic strategies that target both BCR::ABL1-dependent and BCR::ABL1-independent mechanisms of resistance. The combination treatment strategies that target alternative survival signalling, which may contribute towards BCR::ABL1-independent resistance, could be a successful strategy for eradicating residual leukaemic cells and consequently increasing the response rate in CML patients.

Investigating longitudinal changes to frontal cortico-striatal tracts in Huntington's disease: the IMAGE-HD study

The striatum is the principal site of disease pathology in Huntington's disease and contains neural connections to numerous cortical brain regions. Studies examining abnormalities to neural connections find that white matter integrity is compromised in HD; however, further regional, and longitudinal investigation is required. This paper is the first longitudinal investigation into region-based white-matter integrity changes in Huntington's Disease. The aim of this study was to better understand how disease progression impacts white matter tracts connecting the striatum to the prefrontal and motor cortical regions in HD. We used existing neuroimaging data from IMAGE-HD, comprised of 25 pre-symptomatic, 27 symptomatic, and 25 healthy controls at three separate time points (baseline, 18-months, 30-months). Fractional anisotropy, axial diffusivity and radial diffusivity were derived as measures of white matter microstructure. The anatomical regions of interest were identified using the Desikan-Killiany brain atlas. A Group by Time repeated measures ANCOVA was conducted for each tract of interest and for each measure. We found significantly lower fractional anisotropy and significantly higher radial diffusivity in the symptomatic group, compared to both the pre-symptomatic group and controls (the latter two groups did not differ from each other), in the rostral middle frontal and superior frontal tracts; as well as significantly higher axial diffusivity in the rostral middle tracts only. We did not find a Group by Time interaction for any of the white matter integrity measures. These findings demonstrate that whilst the microstructure of white matter tracts, extending from the striatum to these regions of interest, are compromised during the symptomatic stages of Huntington's disease, 36-month follow-up did not show progressive changes in these measures. Additionally, no correlations were found between clinical measures and tractography changes, indicating further investigations into the relationship between tractography changes and clinical symptoms in Huntington's disease are required.

A Gut Instinct on Leukaemia: A New Mechanistic Hypothesis for Microbiota-Immune Crosstalk in Disease Progression and Relapse

Despite significant advances in the treatment of Chronic Myeloid and Acute Lymphoblastic Leukaemia (CML and ALL, respectively), disease progression and relapse remain a major problem. Growing evidence indicates the loss of immune surveillance of residual leukaemic cells as one of the main contributors to disease recurrence and relapse. More recently, there was an appreciation for how the host’s gut microbiota predisposes to relapse given its potent immunomodulatory capacity. This is especially compelling in haematological malignancies where changes in the gut microbiota have been identified after treatment, persisting in some patients for years after the completion of treatment. In this hypothesis-generating review, we discuss the interaction between the gut microbiota and treatment responses, and its capacity to influence the risk of relapse in both CML and ALL We hypothesize that the gut microbiota contributes to the creation of an immunosuppressive microenvironment, which promotes tumour progression and relapse.

Longitudinal mapping of cortical surface changes in Huntington's Disease

This paper investigated cortical folding in Huntington's disease to understand how disease progression impacts the surface of the cortex. Cortical morphometry changes in eight gyral based regions of interest (i.e. the left and right hemispheres of the lateral occipital, precentral, superior frontal and rostral middle gyri) were examined. We used existing neuroimaging data from IMAGE-HD, comprising 26 pre-symptomatic, 26 symptomatic and 24 healthy control individuals at three separate time points (baseline, 18-month, 30-month). Local gyrification index and cortical thickness were derived as the measures of cortical morphometry using FreeSurfer 6.0's longitudinal pipeline. The gyral based regions of interest were identified using the Desikan-Killiany Atlas. A Group by Time repeated measures ANCOVA was conducted for each region of interest. We found significantly lower LGI at a group level in the right hemisphere lateral occipital region and both hemispheres of the precentral region; as well as significantly reduced cortical thickness at a group level in both hemispheres of the lateral occipital and precentral regions and the right hemisphere of the superior frontal region. We also found a Group by Time interaction for Local gyrification index in the right hemisphere lateral occipital region. This change was largely driven by a significant decrease in the symptomatic group between baseline and 18-months. Additionally, lower local gyrification index and cortical thickness were associated with higher disease burden score. These findings demonstrate that significant longitudinal decline in right hemisphere local gyrification index is evident during manifest disease in lateral occipital cortex and that these changes are more profound in individuals with greater disease burden score.

ENIGMA-Sleep: Challenges, opportunities, and the road map

Neuroimaging and genetics studies have advanced our understanding of the neurobiology of sleep and its disorders. However, individual studies usually have limitations to identifying consistent and reproducible effects, including modest sample sizes, heterogeneous clinical characteristics and varied methodologies. These issues call for a large-scale multi-centre effort in sleep research, in order to increase the number of samples, and harmonize the methods of data collection, preprocessing and analysis using pre-registered well-established protocols. The Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA) consortium provides a powerful collaborative framework for combining datasets across individual sites. Recently, we have launched the ENIGMA-Sleep working group with the collaboration of several institutes from 15 countries to perform large-scale worldwide neuroimaging and genetics studies for better understanding the neurobiology of impaired sleep quality in population-based healthy individuals, the neural consequences of sleep deprivation, pathophysiology of sleep disorders, as well as neural correlates of sleep disturbances across various neuropsychiatric disorders. In this introductory review, we describe the details of our currently available datasets and our ongoing projects in the ENIGMA-Sleep group, and discuss both the potential challenges and opportunities of a collaborative initiative in sleep medicine.

Individual differences in attentional lapses are associated with fiber-specific white matter microstructure in healthy adults

Attentional lapses interfere with goal-directed behaviors, which may result in harmless (e.g., not hearing instructions) or severe (e.g., fatal car accident) consequences. Task-related functional MRI (fMRI) studies have shown a link between attentional lapses and activity in the frontoparietal network. Activity in this network is likely to be mediated by the organization of the white matter fiber pathways that connect the regions implicated in the network, such as the superior longitudinal fasciculus I (SLF-I). In the present study, we investigate the relationship between susceptibility to attentional lapses and relevant white matter pathways in 36 healthy adults (23 females, M_age  = 31.56 years). Participants underwent a diffusion MRI (dMRI) scan and completed the global-local task to measure attentional lapses, similar to previous fMRI studies. Applying the fixel-based analysis framework for fiber-specific analysis of dMRI data, we investigated the association between attentional lapses and variability in microstructural fiber density (FD) and macrostructural (morphological) fiber-bundle cross section (FC) in the SLF-I. Our results revealed a significant negative association between higher total number of attentional lapses and lower FD in the left SLF-I. This finding indicates that the variation in the microstructure of a key frontoparietal white matter tract is associated with attentional lapses and may provide a trait-like biomarker in the general population. However, SLF-I microstructure alone does not explain propensity for attentional lapses, as other factors such as sleep deprivation or underlying psychological conditions (e.g., sleep disorders) may also lead to higher susceptibility in both healthy people and those with neurological disorders.

Navigating the link between processing speed and network communication in the human brain

Processing speed on cognitive tasks relies upon efficient communication between widespread regions of the brain. Recently, novel methods of quantifying network communication like 'navigation efficiency' have emerged, which aim to be more biologically plausible compared to traditional shortest path length-based measures. However, it is still unclear whether there is a direct link between these communication measures and processing speed. We tested this relationship in forty-five healthy adults (27 females), where processing speed was defined as decision-making time and measured using drift rate from the hierarchical drift diffusion model. Communication measures were calculated from a graph theoretical analysis of the whole-brain structural connectome and of a task-relevant fronto-parietal structural subnetwork, using the large-scale Desikan-Killiany atlas. We found that faster processing speed on trials that require greater cognitive control are correlated with higher navigation efficiency (of both the whole-brain and the task-relevant subnetwork). In contrast, faster processing speed on trials that require more automatic processing are correlated with shorter path length within the task-relevant subnetwork. Our findings reveal that differences in the way communication is modelled between shortest path length and navigation may be sensitive to processing of automatic and controlled responses, respectively. Further, our findings suggest that there is a relationship between the speed of cognitive processing and the structural constraints of the human brain network.

Longitudinal fixel-based analysis reveals restoration of white matter alterations following balance training in young brain-injured patients

BACKGROUND AND OBJECTIVES

Traumatic brain injury (TBI) is one of the leading causes of death and disability in children and adolescents. Young TBI patients suffer from gross motor deficits, such as postural control deficits, which can severely compromise their daily life activities. However, little attention has been devoted to uncovering the underlying white matter changes in response to training in TBI. In this study, we used longitudinal fixel-based analysis (FBA), an advanced diffusion imaging analysis technique, to investigate the effect of a balance training program on white matter fibre density and morphology in a group of young TBI patients.

METHODS

Young patients with moderate-to-severe TBI (N = 17, 10 females, mean age = 13 ± 3 years) and age-matched controls (N = 17) underwent a home-based balance training program. Diffusion MRI scans together with gross motor assessments, including the gross motor items of the Bruininks-Oseretsky Test of Motor Proficiency, the Activities-Specific Balance Confidence (ABC) Scale, and the Sensory Organization Test (SOT) were administered before and at completion of 8-weeks of training. We used FBA to compare microstructural differences in fibre density (FD), macrostructural (morphological) changes in fibre cross-section (FC), and the combined FD and FC (FDC) metric across the whole brain. We then performed a longitudinal analysis to test whether training restores the white matter in the regions found to be damaged before treatment.

RESULTS

Whole-brain fixel-based analysis revealed lower FD and FC in TBI patients compared to the control group across several commissural tracts, association fibres and projection fibres, with FD reductions of up to 50%. Following training, TBI patients showed a significant interaction effect between Group and Time for the SOT test, as well as significant increases in macrostructural white matter (i.e., FC & FDC) in left sensorimotor tracts. The amount of change in FC and FDC over time was, however, not associated with behavioural changes.

DISCUSSION

Our fixel-based findings identified both microstructural and macrostructural abnormalities in young TBI patients. The longitudinal results provide a deeper understanding of the neurobiological mechanisms underlying balance training, which will allow clinicians to make more effective treatment decisions in everyday clinical practice with brain-injured patients.

Patterns of brain function associated with cannabis cue-reactivity in regular cannabis users: a systematic review of fMRI studies

RATIONALE

Regular cannabis use (i.e. ≥ monthly) is highly prevalent, with past year use being reported by ~ 200 million people globally.High reactivity to cannabis cues is a key feature of regular cannabis use and has been ascribed to greater cannabis exposure and craving, but the underlying neurobiology is yet to be systematically integrated.

OBJECTIVES

We aim to systematically summarise the findings from fMRI studies which examined brain function in cannabis users while exposed to cannabis vs neutral stimuli during a cue-reactivity fMRI task.

METHODS

A systematic search of PsycINFO, PubMed and Scopus databases was pre-registered in PROSPERO (CRD42020171750) and conducted following PRISMA guidelines. Eighteen studies met inclusion/exclusion criteria. Samples comprised 918 participants (340 female) aged 16-38 years. Of these, 603 were regular cannabis users, and 315 were controls.

RESULTS

The literature consistently reported greater brain activity in cannabis users while exposed to cannabis vs neutral stimuli in three key brain areas: the striatum, the prefrontal (anterior cingulate, middle frontal) and the parietal cortex (posterior cingulate/precuneus) and additional brain regions (hippocampus, amygdala, thalamus, occipital cortex). Preliminary correlations emerged between cannabis craving and the function of partially overlapping regions (amygdala, striatum, orbitofrontal cortex ).

CONCLUSIONS

Exposure to cannabis-cues may elicit greater brain function and thus trigger cravings in regular cannabis users and thus trigger cannabis craving. Standardised and longitudinal assessments of cannabis use and related problems are required to profile with greater precision the neurobiology of cannabis cue-reactivity, and its role in predicting  cravings and relapse.

Neural responses to food cues in middle to older aged adults: a scoping review of fMRI studies

AIM

Understanding neural responses through functional magnetic resonance imaging (fMRI) to food and food cues in middle-older adults may lead to better treatment options to address the growing issue of malnutrition. This scoping review aimed to determine the extent, range and nature of research using fMRI, related to reward-based regions, in response to food cues in middle to older aged adults (50 years and over).

METHODS

The following databases were systematically searched in July 2019: CINAHL, CENTRAL, Embase, Dissertations and Theses, Ovid Medline, PsycINFO, PsycEXTRA, Scopus and Web of Science. Studies were eligible for inclusion if participants had a mean or median age ≥50 years, utilised and reported outcomes of either a food cue task-related fMRI methodology or resting-state fMRI. Data from included studies were charted, and synthesised narratively.

RESULTS

Twenty-two studies were included. Eighteen studies utilised a task-related design to measure neural activation, two studies measured resting state neural connectivity only and an additional two studies measured both. The fMRI scanning paradigms, food cue tools and procedure of presentation varied markedly. Four studies compared the neural responses to food between younger and older adults, providing no consensus on neural age-related changes to food cues; two studies utilised longitudinal scans.

CONCLUSION

This review identified significant extent, range and nature in the approaches used to assess neuronal activity in response to food cues in adults aged 50 years and over. Future studies are needed to understand the age-related appetite changes whilst considering personal preferences for food cues.

Modelling the Anatomical Distribution of Neurological Events in COVID-19 Patients: A Systematic Review

Background

Neuropathology caused by the coronavirus disease 2019 (COVID-19) has been reported across several studies. The characterisation of the spatial distribution of these pathology remains critical to assess long and short-term neurological sequelae of COVID-19. To this end, Mathematical models can be used to characterise the location and aetiologies underlying COVID-19-related neuropathology.

Method

We performed a systematic review of the literature to quantify the locations of small neurological events identified with magnetic resonance imaging (MRI) among COVID-19 patients. Neurological events were localised into the Desikan-Killiany grey and white matter atlases. A mathematical network diffusion model was then used to test whether the spatial distribution of neurological events could be explained via a linear spread through the structural connectome of the brain.

Findings

We identified 35 articles consisting of 123 patients that assessed the spatial distribution of small neurological events among COVID-19 patients. Of these, 91 patients had grey matter changes, 95 patients had white matter changes and 72 patients had confirmed cerebral microbleeds. White matter events were observed within 14 of 42 white matter bundles from the IIT atlas. The highest proportions (26%) of events were observed within the bilateral corticospinal tracts. The splenium and middle of the corpus callosum were affected in 14% and 9% of the cases respectively. Grey matter events were spatially distributed in the 41 brain regions within the Desikan-Killiany atlas. The highest proportions (∼10%) of the events were observed in areas including the bilateral superior temporal, precentral, and lateral occipital cortices. Sub-cortical events were most frequently identified in the Pallidum. The application of a mathematical network diffusion model suggested that the spatial pattern of the small neurological events in COVID-19 can be modelled with a linear diffusion of spread from epicentres in the bilateral cerebellum and basal ganglia (Pearson's r =0.41, p <0.001, corrected).

Interpretation

To our knowledge, this is the first study to systematically characterise the spatial distribution of small neurological events in COVID-19 patients and test whether the spatial distribution of these events can be explained by a linear diffusion spread model. The location of neurological events is consistent with commonly identified neurological symptoms including alterations in conscious state among COVID-19 patients that require brain imaging. Given the prevalence and severity of these manifestations, clinicians should carefully monitor neurological symptoms within COVID-19 patients and their potential long-term sequelae .

Rate of torque development and striatal shape in individuals with prodromal Huntington's disease

The aim of the present study was to quantify explosive joint torque or the ability to develop joint torque rapidly, typically measured as the rate of torque development, in individuals with prodromal Huntington’s disease and healthy controls and its associations with measures of disease burden and striatal pathology. Twenty prodromal Huntington’s disease and 19 healthy control individuals volunteered for this study. Plantar flexor isometric rate of torque development values were evaluated using isokinetic dynamometry. Pathological changes in striatal shape were evaluated using magnetic resonance imaging. Disease burden was evaluated using the disease burden score and cytosine-adenine-guanine age product score. No statistical differences in the rate of torque development were observed between individuals with prodromal Huntington’s disease and healthy controls. However, significant associations were observed between the rate of torque development values and measures of disease burden (r = −0.42 to −0.69) and striatal pathology (r = 0.71–0.60) in individuals with prodromal Huntington’s disease. We found significant associations between lower rate of torque development values and greater striatal shape deflation and disease burden and striatal pathology in individuals with prodromal Huntington’s disease. While no significant differences in the rate of torque development were found between prodromal Huntington’s disease and healthy controls, the noted associations suggest that differences may emerge as the disease advances, which should be investigated longitudinally in future studies.

Dual tasking impairments are associated with striatal pathology in Huntington's disease

BACKGROUND

Recent findings suggest that individuals with Huntington's disease (HD) have an impaired capacity to execute cognitive and motor tasks simultaneously, or dual task, which gradually worsens as the disease advances. The onset and neuropathological changes mediating impairments in dual tasking in individuals with HD are unclear. The reliability of dual tasking assessments for individuals with HD is also unclear.

OBJECTIVES

To evaluate differences in dual tasking performance between individuals with HD (presymptomatic and prodromal) and matched controls, to investigate associations between striatal volume and dual tasking performance, and to determine the reliability of dual tasking assessments.

METHODS

Twenty individuals with HD (10 presymptomatic and 10 prodromal) and 20 healthy controls were recruited for the study. Individuals undertook four single and dual task assessments, comprising motor (postural stability or force steadiness) and cognitive (simple or complex mental arithmetic) components, with single and dual tasks performed three times each. Participants also undertook a magnetic resonance imaging assessment.

RESULTS

Compared to healthy controls, individuals with presymptomatic and prodromal HD displayed significant deficits in dual tasking, particularly cognitive task performance when concurrently undertaking motor tasks (P < 0.05). The observed deficits in dual tasking were associated with reduced volume in caudate and putamen structures (P < 0.05),however, not with clinical measures of disease burden. An analysis of the reliability of dual tasking assessments revealed moderate to high test-retest reliability [ICC: 0.61-0.99] for individuals with presymptomatic and prodromal HD and healthy controls.

CONCLUSIONS

Individuals with presymptomatic and prodromal HD have significant deficits in dual tasking that are associated with striatal degeneration. Findings also indicate that dual tasking assessments are reliable in individuals presymptomatic and prodromal HD and healthy controls.

The effects of multidisciplinary rehabilitation on neuroimaging, biological, cognitive and motor outcomes in individuals with premanifest Huntington's disease

BACKGROUND

Huntington's disease (HD) is a chronic, progressive neurodegenerative condition for which there are currently no proven disease-modifying therapies. Lifestyle factors have been shown to impact on the age of disease onset and progression of disease features. We therefore investigated the effects of a nine-month multidisciplinary rehabilitation intervention on neuroimaging, biological and clinical disease outcomes in individuals with premanifest HD.

METHODS

31 individuals with premanifest HD participated in the study. Eighteen participants underwent a nine-month multidisciplinary rehabilitation intervention comprising aerobic and resistance exercise, computerised cognitive training, dual-task training and sleep hygiene and nutritional guidance. The remaining 13 participants were allocated to a standard care control group. Neuroimaging, biological, cognitive, motor and cardiorespiratory fitness data was collected.

RESULTS

Participants displayed good adherence (87%) and compliance (85%) to the intervention. Maintenance of the shape of the right putamen was observed in the intervention group when compared to the control group. The intervention group displayed significant improvements in verbal learning and memory, attention, cognitive flexibility and processing speed following the intervention when compared to the control group. Performance on the mini-social cognition and emotional assessment (mini-SEA) was maintained in the intervention group, but decreased in the control group. No changes were observed in serum neurofilament light protein levels, postural stability outcomes or cardiorespiratory fitness.

CONCLUSION

This study adds to the accumulating body of literature to suggest that multidisciplinary rehabilitation is of clinical benefit for individuals with HD. Large randomised controlled trials are necessary to determine the extent to which benefits occur across the spectrum of the disease.

Brain compensation during response inhibition in premanifest Huntington's disease

Premanifest Huntington's disease (pre-HD) individuals typically show increased task-related functional magnetic resonance imaging (fMRI), suggested to reflect compensatory strategies. Despite the evidence, no study has attempted to understand the compensatory process in light of 'formal' models of compensation. We used a quantitative model of compensation - the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH), to characterise compensation in pre-HD using fMRI. Pre-HD individuals (n = 15) and controls (n = 15) performed a modified stop-signal task that incremented in four levels of stop difficulty. Our results did not support the critical assumption of the CRUNCH model - controls did not show increased fMRI activity with increased level of stop difficulty; however, controls showed decreased fMRI activity with increased stop difficulty in right inferior frontal gyrus and right caudate nucleus. Relative to controls, pre-HD individuals showed increased fMRI activity in right inferior frontal gyrus and in right caudate nucleus at higher levels of stop difficulty, which is the opposite effect to that predicted by the model. Our findings suggest a compensatory process of the response inhibition network in pre-HD; however, the pattern of fMRI activity was not in the manner expected by CRUNCH.

International Mind, Activities and Urban Places (iMAP) study: methods of a cohort study on environmental and lifestyle influences on brain and cognitive health

INTRODUCTION

Numerous studies have found associations between characteristics of urban environments and risk factors for dementia and cognitive decline, such as physical inactivity and obesity. However, the contribution of urban environments to brain and cognitive health has been seldom examined directly. This cohort study investigates the extent to which and how a wide range of characteristics of urban environments influence brain and cognitive health via lifestyle behaviours in mid-aged and older adults in three cities across three continents.

METHODS AND ANALYSIS

Participants aged 50-79 years and living in preselected areas stratified by walkability, air pollution and socioeconomic status are being recruited in Melbourne (Australia), Barcelona (Spain) and Hong Kong (China) (n=1800 total; 600 per site). Two assessments taken 24 months apart will capture changes in brain and cognitive health. Cognitive function is gauged with a battery of eight standardised tests. Brain health is assessed using MRI scans in a subset of participants. Information on participants' visited locations is collected via an interactive web-based mapping application and smartphone geolocation data. Environmental characteristics of visited locations, including the built and natural environments and their by-products (e.g., air pollution), are assessed using geographical information systems, online environmental audits and self-reports. Data on travel and lifestyle behaviours (e.g., physical and social activities) and participants' characteristics (e.g., sociodemographics) are collected using objective and/or self-report measures.

ETHICS AND DISSEMINATION

The study has been approved by the Human Research Ethics Committee of the Australian Catholic University, the Institutional Review Board of the University of Hong Kong and the Parc de Salut Mar Clinical Research Ethics Committee of the Government of Catalonia. Results will be communicated through standard scientific channels. Methods will be made freely available via a study-dedicated website.

TRIAL REGISTRATION NUMBER

ACTRN12619000817145.

Oxytocin selectively modulates brain processing of disgust in Huntington's disease gene carriers

People with Huntington's disease (HD) exhibit altered processing of emotional information, especially disgust and other negative emotions. These impairments are likely due to the effects of the disease on underlying brain networks. We examined whether oxytocin, when given intranasally, would normalise aberrant brain reactivity to emotional faces in participants with the gene-expansion for HD. In a double-blind placebo-controlled cross-over design, we measured brain activity, using functional magnetic resonance imaging, whilst nine medication-free HD carriers, and ten control participants viewed emotional (disgust, fear, angry, sad, surprise, happy) and neutral faces, following acute intranasal oxytocin (24IU) and placebo. Subjective mood changes were assessed before and after the neuroimaging on each visit. Permutation-based non-parametric statistical testing for the whole brain, showed significant group×drug interactions (p's<0.05, TFCE corrected) in areas of the left frontal pole, superior frontal, and middle frontal gyri cortically, and left putamen and thalamus sub-cortically. Parameter estimates extracted from the middle frontal gyrus and putamen showed that, under placebo, the HD group had lower brain activity to disgust stimuli, compared with controls. After intranasal oxytocin, the pattern of activation to disgust stimuli was normalised in the HD group to similar levels as controls; eight of the nine HD carriers showed increased response in the middle frontal gyrus, and seven of the nine HD carriers showed increased response in the putamen. The observed effects of oxytocin occurred in the absence of changes in subjective mood or state anxiety. These findings provide early evidence for a physiological role of oxytocin in the neuropathology of HD. Our findings are the first reported oxytocin effects in a neurodegenerative disease. Further research should examine the therapeutic benefits of oxytocin in alleviating emotional and social cognition deficits in HD and related disorders.

Emotion processing in persons who respond vicariously towards others in pain: Disinhibited left-lateralized neural activity for threatening expressions

We investigated emotional processing in vicarious pain (VP) responders. VP responders report an explicit sensory and emotional feeling of pain when they witness another in pain, which is greater in magnitude than the empathic processing of pain in the general population. In Study 1, 31 participants completed a chimeric faces task, judging whether emotional chimera in the left, or right, visual field was more intense. VP responders took longer to judge emotionality than non-responders, and fixated more on the angry hemiface in the right visual field, whereas non-responder controls had no lateralized fixation bias. In Study 2, blood-oxygen level-dependent signals were recorded during an emotional face matching task. VP intensity was correlated with increased insula activity and reduced middle frontal gyrus activity for angry faces, and with reduced activity in the inferior and middle frontal gyri for sad faces. Together, these findings suggest that VP responders are more reactive to negative emotional expressions. Specifically, emotional judgements involved altered left-hemisphere activity in VP responders, and reduced engagement of regions involved in emotion regulation.

Multimodal imaging biomarkers in premanifest and early Huntington's disease: 30-month IMAGE-HD data

BACKGROUND

The discovery of potential disease-modifying therapies in a neurodegenerative condition like Huntington's disease depends on the availability of sensitive biomarkers that reflect decline across disease stages and that are functionally and clinically relevant.

AIMS

To quantify macrostructural and microstructural changes in participants with premanifest and symptomatic Huntington's disease over 30 months, and to establish their functional and clinical relevance.

METHOD

Multimodal magnetic resonance imaging study measuring changes in macrostructural (volume) and microstructural (diffusivity) measures in 40 patients with premanifest Huntington's disease, 36 patients with symptomatic Huntington's disease and 36 healthy control participants over three testing sessions spanning 30 months.

RESULTS

Relative to controls, there was greater longitudinal atrophy in participants with symptomatic Huntington's disease in whole brain, grey matter, caudate and putamen, as well as increased caudate fractional anisotropy; caudate volume loss was the only measure to differ between premanifest Huntington's disease and control groups. Changes in caudate volume and fractional anisotropy correlated with each other and neurocognitive decline; caudate volume loss also correlated with clinical and disease severity.

CONCLUSIONS

Caudate neurodegeneration, especially atrophy, may be the most suitable candidate surrogate biomarker for consideration in the development of upcoming clinical trials.

Iron accumulation in the basal ganglia in Huntington's disease: cross-sectional data from the IMAGE-HD study

OBJECTIVES

To measure iron accumulation in the basal ganglia in Huntington's disease (HD) using quantitative susceptibility mapping (QSM), and to ascertain its relevance in terms of clinical and disease severity.

METHODS

In this cross-sectional investigation, T2* weighted imaging was undertaken on 31 premanifest HD, 32 symptomatic HD and 30 control participants as part of the observational IMAGE-HD study. Group differences in iron accumulation were ascertained with QSM. Associations between susceptibility values and disease severity were also investigated.

RESULTS

Compared with controls, both premanifest and symptomatic HD groups showed significantly greater iron content in pallidum, putamen and caudate. Additionally, iron accumulation in both putamen and caudate was significantly associated with disease severity.

CONCLUSIONS

These findings provide the first evidence that QSM is sensitive to iron deposition in subcortical target areas across premanifest and symptomatic stages of HD. Such findings could open up new avenues for biomarker development and therapeutic intervention.

Characterising Upper Limb Movements in Huntington's Disease and the Impact of Restricted Visual Cues

BACKGROUND

Voluntary motor deficits are a common feature in Huntington's disease (HD), characterised by movement slowing and performance inaccuracies. This deficit may be exacerbated when visual cues are restricted.

OBJECTIVE

To characterize the upper limb motor profile in HD with various levels of difficulty, with and without visual targets.

METHODS

Nine premanifest HD (pre-HD), nine early symptomatic HD (symp-HD) and nine matched controls completed a motor task incorporating Fitts' law, a model of human movement enabling the quantification of movement timing, via the manipulation of task difficulty (i.e., target size, and distance between targets). The task required participants to make reciprocal movements under cued and blind conditions. Dwell times (time stationary between movements), speed, accuracy and variability of movements were compared between groups.

RESULTS

Symp-HD showed significantly prolonged and less consistent movement times, compared with controls and pre-HD. Furthermore, movement planning and online control were significantly impaired in symp-HD, compared with controls and pre-HD, evidenced by prolonged dwell times and deceleration times. Speed and accuracy were comparable across groups, suggesting that group differences observed in movement time, variability, dwell time and deceleration time were evident over and above simple performance measures. The presence of cues resulted in greater movement time variability in symp-HD, compared with pre-HD and controls, suggesting that the deficit in movement consistency manifested only in response to targeted movements.

CONCLUSIONS

Collectively, these findings provide evidence of a deficiency in both motor planning, particularly in relation to movement timing and online control, which became exacerbated as a function of task difficulty during symp-HD stages. These variables may provide a more sensitive measure of motor dysfunction than speed and/or accuracy alone in symp-HD.

The multi-modal Australian ScienceS Imaging and Visualization Environment (MASSIVE) high performance computing infrastructure: applications in neuroscience and neuroinformatics research

The Multi-modal Australian ScienceS Imaging and Visualization Environment (MASSIVE) is a national imaging and visualization facility established by Monash University, the Australian Synchrotron, the Commonwealth Scientific Industrial Research Organization (CSIRO), and the Victorian Partnership for Advanced Computing (VPAC), with funding from the National Computational Infrastructure and the Victorian Government. The MASSIVE facility provides hardware, software, and expertise to drive research in the biomedical sciences, particularly advanced brain imaging research using synchrotron x-ray and infrared imaging, functional and structural magnetic resonance imaging (MRI), x-ray computer tomography (CT), electron microscopy and optical microscopy. The development of MASSIVE has been based on best practice in system integration methodologies, frameworks, and architectures. The facility has: (i) integrated multiple different neuroimaging analysis software components, (ii) enabled cross-platform and cross-modality integration of neuroinformatics tools, and (iii) brought together neuroimaging databases and analysis workflows. MASSIVE is now operational as a nationally distributed and integrated facility for neuroinfomatics and brain imaging research.

Functional magnetic resonance imaging of working memory in Huntington's disease: cross-sectional data from the IMAGE-HD study

We used functional magnetic resonance imaging (fMRI) to investigate spatial working memory (WM) in an N-BACK task (0, 1, and 2-BACK) in premanifest Huntington's disease (pre-HD, n = 35), early symptomatic Huntington's disease (symp-HD, n = 23), and control (n = 32) individuals. Overall, both WM conditions (1-BACK and 2-BACK) activated a large network of regions throughout the brain, common to all groups. However, voxel-wise and time-course analyses revealed significant functional group differences, despite no significant behavioral performance differences. During 1-BACK, voxel-wise blood-oxygen-level-dependent (BOLD) signal activity was significantly reduced in a number of regions from the WM network (inferior frontal gyrus, anterior insula, caudate, putamen, and cerebellum) in pre-HD and symp-HD groups, compared with controls; however, time-course analysis of the BOLD response in the dorsolateral prefrontal cortex (DLPFC) showed increased activation in symp-HD, compared with pre-HD and controls. The pattern of reduced voxel-wise BOLD activity in pre-HD and symp-HD, relative to controls, became more pervasive during 2-BACK affecting the same structures as in 1-BACK, but also incorporated further WM regions (anterior cingulate gyrus, parietal lobe and thalamus). The DLPFC BOLD time-course for 2-BACK showed a reversed pattern to that observed in 1-BACK, with a significantly diminished signal in symp-HD, relative to pre-HD and controls. Our findings provide support for functional brain reorganisation in cortical and subcortical regions in both pre-HD and symp-HD, which are modulated by task difficulty. Moreover, the lack of a robust striatal BOLD signal in pre-HD may represent a very early signature of change observed up to 15 years prior to clinical diagnosis.

Electromagnetic tomography via source-space-ICA

We propose a technique, called source-space-ICA to provide spatiotemporal reconstruction of brain sources. First, the weight-vector-normalized minimum variance beamformer is applied to reconstruct the electrical activity of a 3D scanning grid which covers the whole brain. Second, principal component analysis is used to reduce the dimension of the reconstructed signal matrix of the source-space, then independent component analysis (ICA) is applied on the resulting matrix to identify multiple signal sources in the source-space. Third, the demixing weight vectors obtained by ICA for the identified independent components are projected back into the SS to obtain tomographic maps of the sources. Besides localization, the proposed source-space-ICA approach reconstructs the time-course of each source in a single time-series without requiring prior knowledge of location, orientation, and number of sources for a given segment of EEG/MEG. Simulated EEG was used to evaluate the source-space-ICA. The results show that the source-space-ICA approach is able to separate and localize multiple weak sources and is robust to interference from other sources as it identifies the sources based on their statistical independence.

Performance of beamformers on EEG source reconstruction

Recently a number of new beamformers have been introduced for reconstruction and localization of neural sources from EEG and MEG. However, little is known about the relative performance of these beamformers. In this study, 8 scalar beamformers were examined with respect to several parameters to determine how effective they are at reconstruction of a dipole time course from EEG. A simulated EEG signal was produced by means of forward head modelling for projection of an artificial dipole on scalp electrodes then superimposed on background signal. Both real EEG and white noise were applied as background activity. Although the eigenspace beamformer can perform slightly better than other beamformers for small dipoles, and even more so for large dipoles, it is not a contender for real-time beamforming of EEG as it cannot be completely automated. Overall, in terms of performance, robustness to variations in parameters, and ease of application, the minimum variance and Borgiotti-Kaplan beamformers were found to be the best performers.