Loss in connectivity among regions of the brain reward system in alcohol dependence

Altered structural connectivity and functional brain dynamics in individuals with heavy alcohol use elucidated via network control theory

BACKGROUND

Heavy alcohol use (HAU) and its associated conditions, such as alcohol use disorder (AUD), impact millions of individuals worldwide. While our understanding of the neurobiological correlates of alcohol use has evolved substantially, we still lack models incorporating whole-brain neuroanatomical, functional, and pharmacological information under one framework.

METHODS

Here, we utilize diffusion and functional magnetic resonance imaging to investigate alterations to brain dynamics in N = 130 individuals with a high amount of current alcohol use. We compared these alcohol using individuals to N = 308 individuals with minimal use of any substances.

RESULTS

We find that individuals with HAU had less dynamic and complex brain activity, and through leveraging network control theory, had increased control energy to complete transitions between activation states. Further, using separately acquired positron emission tomography (PET) data, we deploy an in silico evaluation demonstrating that decreased D2 receptor levels, as found previously in individuals with AUD, may relate to our observed findings.

CONCLUSIONS

This work demonstrates that whole-brain, multimodal imaging information can be combined under a network control framework to identify and evaluate neurobiological correlates and mechanisms of heavy alcohol use.

Altered structural connectivity and functional brain dynamics in individuals with heavy alcohol use

Heavy alcohol use and its associated conditions, such as alcohol use disorder (AUD), impact millions of individuals worldwide. While our understanding of the neurobiological correlates of AUD has evolved substantially, we still lack models incorporating whole-brain neuroanatomical, functional, and pharmacological information under one framework. Here, we utilize diffusion and functional magnetic resonance imaging to investigate alterations to brain dynamics in N = 130 individuals with a high amount of current alcohol use. We compared these alcohol using individuals to N = 308 individuals with minimal use of any substances. We find that individuals with heavy alcohol use had less dynamic and complex brain activity, and through leveraging network control theory, had increased control energy to complete transitions between activation states. Further, using separately acquired positron emission tomography (PET) data, we deploy an in silico evaluation demonstrating that decreased D2 receptor levels, as found previously in individuals with AUD, may relate to our observed findings. This work demonstrates that whole-brain, multimodal imaging information can be combined under a network control framework to identify and evaluate neurobiological correlates and mechanisms of AUD.

Early onset adolescent binge drinking is associated with reduced white matter integrity in post-9/11 adult veterans

Adolescence represents a critical period of neural development during which binge drinking (BD) is prevalent. Though prior work has shown that white matter (WM) integrity is susceptible to damage from excessive alcohol intake in adults, the effect of early adolescent BD on WM health in adulthood remains unknown. Veterans with a history of BD onset before age 15 [n = 49; mean age = 31.8 years; early-onset adolescent binge drinkers (EBD)] and after age 15 [n = 290; mean age = 32.2 years; late-onset adolescent binge drinkers (LBD)] were studied with diffusion tensor imaging. Group differences in fractional anisotropy (FA; movement of water molecules along the WM) and mean diffusivity (MD; average movement of water molecules) were examined as indices of WM integrity using FreeSurfer and FMRIB Software Library (FSL) processing streams. Lower FA and higher MD are thought to represent degradations in WM integrity. A reference group (RG) of social drinkers with no history of BD (n = 31) was used to provide comparative normative data. We observed widespread decreased FA and increased MD in EBDs, compared to LBDs, as well as decreased FA in the pars triangularis, lateral orbitofrontal cortex, superior frontal cortex, isthmus cingulate, and genu and splenium of the corpus callosum EBDs also had lower WM integrity compared to the RG. Adults who initiated BD during early adolescence demonstrated decreased FA and increased MD throughout the frontostriatal circuits that mediate inhibitory control and thus may result in impulsive behavior and a predisposition for developing alcohol use disorder during adulthood.

Anomalies in global network connectivity associated with early recovery from alcohol dependence: A network transcranial magnetic stimulation and electroencephalography study

Although previous research in alcohol dependent populations identified alterations within local structures of the addiction ‘reward’ circuitry, there is limited research into global features of this network, especially in early recovery. Transcranial magnetic stimulation (TMS) is capable of non‐invasively perturbing the brain network while electroencephalography (EEG) measures the network response. The current study is the first to apply a TMS inhibitory paradigm while utilising network science (graph theory) to quantify network anomalies associated with alcohol dependence. Eleven individuals with alcohol‐dependence (ALD) in early recovery and 16 healthy controls (HC) were administered 75 single pulses and 75 paired‐pulses (inhibitory paradigm) to both the left and right prefrontal cortex (PFC). For each participant, Pearson cross‐correlation was applied to the EEG data and correlation matrices constructed. Global network measures (mean degree, clustering coefficient, local efficiency and global efficiency) were extracted for comparison between groups. Following administration of the inhibitory paired‐pulse TMS to the left PFC, the ALD group exhibited altered mean degree, clustering coefficient, local efficiency and global efficiency compared to HC. Decreases in local efficiency increased the prediction of being in the ALD group, while all network metrics (following paired‐pulse left TMS) were able to adequately discriminate between the groups. In the ALD group, reduced mean degree and global clustering was associated with increased severity of past alcohol use. Our study provides preliminary evidence of altered network topology in patients with alcohol dependence in early recovery. Network anomalies were predictive of high alcohol use and correlated with clinical features of alcohol dependence. Further research using this novel brain mapping technique may identify useful network biomarkers of alcohol dependence and recovery.

A coordinate-based meta-analysis of white matter alterations in patients with alcohol use disorder

INTRODUCTION

Besides the commonly described gray matter (GM) deficits, there is growing evidence of significant white matter (WM) alterations in patients with alcohol use disorder (AUD). WM changes can be assessed using volumetric and diffusive magnetic resonance imaging methods, such as voxel-based morphometry (VBM) and diffusion tensor imaging (DTI). The aim of the present meta-analysis is to investigate the spatial convergence of the reported findings on WM alterations in AUD.

METHODS

Systematic literature search on PubMed and further databases revealed 18 studies eligible for inclusion, entailing a total of 462 AUD patients and 416 healthy controls (up to January 18, 2021). All studies that had used either VBM or DTI whole-brain analyzing methods and reported results as peak-coordinates in standard reference space were considered for inclusion. We excluded studies using approaches non-concordant with recent guidelines for neuroimaging meta-analyses and studies investigating patient groups with Korsakoff syndrome or other comorbid substance use disorders (except tobacco).

RESULTS

Anatomical likelihood estimation (ALE) revealed four significant clusters of convergent macro- and microstructural WM alterations in AUD patients that were assigned to the genu and body of the corpus callosum, anterior and posterior cingulum, fornix, and the right posterior limb of the internal capsule.

DISCUSSION

The changes in WM could to some extent explain the deteriorations in motor, cognitive, affective, and perceptual functions seen in AUD. Future studies are needed to clarify how WM alterations vary over the course of the disorder and to what extent they are reversible with prolonged abstinence.

Alcohol use in emerging adults associated with lower rich-club connectivity and greater connectome network disorganization

BACKGROUND

Emerging adulthood is a critical neurodevelopmental stage, with alcohol use during this period consistently associated with brain abnormalities and damage in anatomical structure and white matter integrity. However, it is less clear how alcohol use is associated with the brain's structural organization (i.e., white matter connections between anatomical regions). Recent connectome research has focused on rich-club regions, a collection of highly-interconnected hubs that are critical in brain communication and global network organization and disproportionately vulnerable to insults.

METHODS

For the first time, we examined alcohol use associations with structural rich-club and connectome organization in emerging adults (N = 66).

RESULTS

Greater lifetime drinks and current monthly drinks were significantly associated with lower rich-club organization (r_s =-0.38, ps < 0.003) and lower rich-club connectivity (r_s <-0.34, ps < 0.007). Additionally, rich-club connectivity was significantly more negatively correlated with alcohol use than connectivity among non-rich-club regions (ps < 0.035). Examining overall structural organization, greater lifetime drinks and current monthly drinks were significantly associated with lower network density (i.e., lower network resilience; r_s <-0.36, ps = 0.004). Additionally, greater lifetime drinks and current monthly drinks were significantly associated with higher network segregation (i.e., network's tendency to divide into subnetworks; r_s >0.33, ps<0.008). Alcohol use was not significantly associated with network integration (i.e., network's efficiency in combining information across the brain; ps > 0.064).

CONCLUSIONS

Results provide novel evidence that alcohol use is associated with decreased rich-club connectivity and structural network disorganization. Given that both are critical in global brain communication, these results highlight the importance of examining alcohol use and brain relationships in emerging adulthood.

The gray matter structural connectome and its relationship to alcohol relapse: Reconnecting for recovery

Gray matter (GM) atrophy associated with alcohol use disorders (AUD) affects predominantly the frontal lobes. Less is known how frontal lobe GM loss affects GM loss in other regions and how it influences drinking behavior or relapse after treatment. The profile similarity index (PSI) combined with graph analysis allows to assess how GM loss in one region affects GM loss in regions connected to it, ie, GM connectivity. The PSI was used to describe the pattern of GM connectivity in 21 light drinkers (LDs) and in 54 individuals with AUD (ALC) early in abstinence. Effects of abstinence and relapse were determined in a subgroup of 36 participants after 3 months. Compared with LD, GM losses within the extended brain reward system (eBRS) at 1-month abstinence were similar between abstainers (ABST) and relapsers (REL), but REL had also GM losses outside the eBRS. Lower GM connectivities in ventro-striatal/hypothalamic and dorsolateral prefrontal regions and thalami were present in both ABST and REL. Between-networks connectivity loss of the eBRS in ABST was confined to prefrontal regions. About 3 months later, the GM volume and connectivity losses had resolved in ABST, and insula connectivity was increased compared with LD. GM losses and GM connectivity losses in REL were unchanged. Overall, prolonged abstinence was associated with a normalization of within-eBRS connectivity and a reconnection of eBRS structures with other networks. The re-formation of structural connectivities within and across networks appears critical for cognitive-behavioral functioning related to the capacity to maintain abstinence after outpatient treatment.

Microstructural damage of white-matter tracts connecting large-scale networks is related to impaired executive profile in alcohol use disorder

Alcohol Use Disorders (AUD) is associated with negative consequences on global functioning, likely reflecting chronic changes in brain morphology and connectivity. Previous attempts to characterize cognitive impairment in AUD addressed patients' performance in single domains, without considering their cognitive profile as a whole. While altered cognitive performance likely reflects abnormal white-matter microstructural properties, to date no study has directly addressed the relationship between a proxy of patients' cognitive profile and microstructural damage. To fill this gap we aimed to characterize the microstructural damage pattern, and its relationship with cognitive profile, in treatment-seeking AUD patients. Twenty-two AUD patients and 18 healthy controls underwent a multimodal MRI protocol including diffusion tensor imaging (DTI), alongside a comprehensive neurocognitive assessment. We used a principal component analysis (PCA) to identify superordinate components maximally explaining variability in cognitive performance, and whole-brain voxelwise analyses to unveil the neural correlates of AUD patients' cognitive impairment in terms of different white-matter microstructural features, i.e. fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD). PCA revealed a basic executive component, significantly impaired in AUD patients, associated with tasks tapping visuo-motor processing speed, attention and working-memory. Within a widespread pattern of white-matter damage in patients, we found diverse types of relationship linking WM microstructure and executive performance: (i) in the whole sample, we observed a linear relationship involving MD/RD metrics within both 'superficial' white-matter systems mediating connectivity within large-scale brain networks, and deeper systems modulating their reciprocal connections; (ii) in AUD patients vs. controls, a performance-by-group interaction highlighted a MD/AD pattern involving two frontal white-matter systems, including the genu of corpus callosum and cingulum bundle, mediating structural connectivity among central executive, salience and default mode networks. Alterations of prefrontal white-matter pathways are suggestive of abnormal structural connectivity in AUD, whereby a defective interplay among large-scale networks underpins patients' executive dysfunction. These findings highlight different directions for future basic and translational research aiming to tailor novel rehabilitation strategies and assess their functional outcomes.

Role of Patient Sex in Early Recovery from Alcohol-Related Cognitive Impairment: Women Penalized

BACKGROUND

The objective was to explore the role of patient sex in cognitive recovery and to identify predictive factors for non-recovery in alcohol use disorder (AUD).

METHODS

All patients with AUD admitted to a residential addictions treatment center were systematically assessed at admission and after 6 weeks of abstinence in a controlled environment. The inclusion criteria were that patients were admitted for AUD with baseline alcohol-related cognitive impairment (baseline total Montreal Cognitive Assessment (MoCA) score < 26) and reassessed at 6 weeks (n = 395). A logistic regression model was built to determine the influence of sex on recovery status (MoCA < or ≥ 26) taking into account the interaction effect of sex with alcohol consumption on cognitive function.

RESULTS

The mean age was 50.10 years (SD = 9.79), and 27.41% were women. At baseline, the mean MoCA scores were 21.36 (SD = 3.04). Participants who did not achieve recovery (59.3% of women vs 53.8% of men) had lower total MoCA scores at baseline. The 2 factors that was significantly and independently associated with non-recovery and with a non-zero coefficient was being a woman and initial MoCA score (respective adjusted odds ratios (AOR) = 1.5 and 0.96, p-values < 0.05).

CONCLUSIONS

These results could influence the time required in a controlled environment to maintain abstinence and the duration of in-care for women.

Repetitive transcranial magnetic stimulation: Re-wiring the alcoholic human brain

Alcohol use disorders (AUDs) are one of the leading causes of mortality and morbidity worldwide. In spite of significant advances in understanding the neural underpinnings of AUDs, therapeutic options remain limited. Recent studies have highlighted the potential of repetitive transcranial magnetic stimulation (rTMS) as an innovative, safe, and cost-effective treatment for AUDs. Here, we summarize the fundamental principles of rTMS and its putative mechanisms of action via neurocircuitries related to alcohol addiction. We will also discuss advantages and limitations of rTMS, and argue that Hebbian plasticity and connectivity changes, as well as state-dependency, play a role in shaping some of the long-term effects of rTMS. Visual imaging studies will be linked to recent clinical pilot studies describing the effect of rTMS on alcohol craving and intake, pinpointing new advances, and highlighting conceptual gaps to be filled by future controlled studies.

White matter microstructural correlates of relapse in alcohol dependence

Identification of neural correlates of relapse to alcohol after treatment is clinically important as it may inform better substance abuse treatment. Few studies have specifically analyzed the white matter microstructure in treatment seekers as it might relate to relapse risk versus long-term abstinence. Using 4 Tesla diffusion tensor imaging, we compared two groups of one-month-abstinent treatment-seekers, who were classified based on their drinking status between six and nine months after treatment initiation. We hypothesized that subsequent relapsers had greater white matter microstructural deficits in specific brain regions than long-term abstainers. At one month of abstinence, 37 future relapsers versus 25 future abstainers had lower fractional anisotropy (a measure of axonal organization and membrane integrity) in the corpus callosum and right stria terminalis/fornix, higher diffusivity in the genu of the corpus callosum, left and right stria terminalis/fornix, and lower diffusivity in left anterior corona radiata. These differences existed despite similar lifetime and recent drinking and smoking histories in the groups. Longer smoking duration in relapsers was associated with lower fractional anisotropy in right stria terminalis/fornix. The study identified specific microstructural biomarkers of alcohol relapse risk in adults, contributing to the definition of a neurobiological relapse risk profile in alcohol use disorder.

Alcohol use effects on adolescent brain development revealed by simultaneously removing confounding factors, identifying morphometric patterns, and classifying individuals

Group analysis of brain magnetic resonance imaging (MRI) metrics frequently employs generalized additive models (GAM) to remove contributions of confounding factors before identifying cohort specific characteristics. For example, the National Consortium on Alcohol and NeuroDevelopment in Adolescence (NCANDA) used such an approach to identify effects of alcohol misuse on the developing brain. Here, we hypothesized that considering confounding factors before group analysis removes information relevant for distinguishing adolescents with drinking history from those without. To test this hypothesis, we introduce a machine-learning model that identifies cohort-specific, neuromorphometric patterns by simultaneously training a GAM and generic classifier on macrostructural MRI and microstructural diffusion tensor imaging (DTI) metrics and compare it to more traditional group analysis and machine-learning approaches. Using a baseline NCANDA MR dataset (N = 705), the proposed machine learning approach identified a pattern of eight brain regions unique to adolescents who misuse alcohol. Classifying high-drinking adolescents was more accurate with that pattern than using regions identified with alternative approaches. The findings of the joint model approach thus were (1) impartial to confounding factors; (2) relevant to drinking behaviors; and (3) in concurrence with the alcohol literature.

Regional cerebral blood flow in opiate dependence relates to substance use and neuropsychological performance

Neuroimaging of opiate-dependent individuals indicates both altered brain structure and function. Magnetic resonance-based arterial spin labeling has been used to measure noninvasively cerebral blood flow (i.e. perfusion) in alcohol, tobacco and stimulant dependence; only one arterial spin labeling paper in opiate-dependent individuals demonstrated frontal and parietal perfusion deficits. Additional research on regional brain perfusion in opiate dependence and its relationship to cognition and self-regulation (impulsivity, risk taking and decision making) may inform treatment approaches for opiate-dependent individuals. Continuous arterial spin labeling magnetic resonance imaging at 4 T and neuropsychological measures assessed absolute brain perfusion levels, cognition and self-regulation in 18 cigarette smoking opiate-dependent individuals (sODI) stable on buprenorphine maintenance therapy. The sODI were compared with 20 abstinent smoking alcohol-dependent individuals (a substance-dependent control group), 35 smoking controls and 29 nonsmoking controls. sODI had lower perfusion in several cortical and subcortical regions including regions within the brain reward/executive oversight system compared with smoking alcohol-dependent individuals and nonsmoking controls. Perfusion was increased in anterior cingulate cortex and globus pallidus of sODI. Compared with all other groups, sODI had greater age-related declines in perfusion in most brain reward/executive oversight system and some other regions. In sODI, lower regional perfusion related to greater substance use, higher impulsivity and weaker visuospatial skills. Overall, sODI showed cortical and subcortical hypoperfusion and hyperperfusion. Relating to neuropsychological performance and substance use quantities, the frontal perfusion alterations are clinically relevant and constitute potential targets for pharmacological and cognitive-based therapeutic interventions to improve treatment outcome in opiate dependence.

A majority rule approach for region-of-interest-guided streamline fiber tractography

Hand-drawn gray matter regions of interest (ROI) are often used to guide the estimation of white matter tractography, obtained from diffusion-weighted magnetic resonance imaging (DWI), in healthy and in patient populations. However, such ROIs are vulnerable to rater bias of the individual segmenting the ROIs, scan variability, and individual differences in neuroanatomy. In this report, a "majority rule" approach is introduced for ROI segmentation used to guide streamline tractography in white matter structures. DWI of one healthy participant was acquired in ten separate sessions using a 3 T scanner over the course of a month. Four raters identified ROIs within the left hemisphere [Cerebral Peduncle (CPED); Internal Capsule (IC); Hand Portion of the Motor Cortex, or Hand Bump, (HB)] using a group-established standard operating procedure for ROI definition to guide the estimation of streamline tracts within the corticospinal tract (CST). Each rater traced the ROIs twice for each scan session. The overlap of each rater's two ROIs was used to define a representative ROI for each rater. These ROIs were combined to create a "majority rules" ROI, in which the rule requires that each voxel is selected by at least three of four raters. Reproducibility for ROIs and CST segmentations were analyzed with the Dice Similarity Coefficient (DSC). Intra-rater reliability for each ROI was high (DSCs ≥ 0.83). Inter-rater reliability was moderate to adequate (DSC range 0.54-0.75; lowest for IC). Using intersected majority rules ROIs, the resulting CST showed improved overlap (DSC = 0.82) in the estimated streamline tracks for the ten sessions. Despite high intra-rater reliability, there was lower inter-rater reliability consistent with the expectation of rater bias. Employing the majority rules method improved reliability in the overlap of the CST.

Effects of abstinence and chronic cigarette smoking on white matter microstructure in alcohol dependence: Diffusion tensor imaging at 4T

BACKGROUND

We previously reported widespread microstructural deficits of brain white matter in alcohol-dependent individuals (ALC) compared to light drinkers in a small 1.5T diffusion tensor imaging study employing tract-based spatial statistics. Using a larger dataset acquired at 4T, the present study is an extension that investigated the effects of alcohol consumption, abstinence from alcohol, and comorbid cigarette smoking on white matter microstructure.

METHODS

Tract-based spatial statistics were performed on 20 1-week-abstinent ALC, 52 1-month-abstinent ALC, and 30 controls. Regional measures of fractional anisotropy (FA) and mean diffusivity (MD) in the significant clusters were compared by Analysis of Covariance. The metrics were correlated with substance use history and behavioral measures.

RESULTS

1-week-abstinent ALC showed lower FA than controls in the corpus callosum, right cingulum, external capsule, and hippocampus. At 1 month of abstinence, only the FA in the body of the corpus callosum of ALC remained significantly different from controls. Some regional FA deficits correlated with more severe measures of drinking and smoking histories but only weakly with mood and impulsivity measures.

CONCLUSION

White matter microstructure is abnormal during early abstinence in alcohol dependent treatment seekers and recovers into the normal range within about four weeks. The compromised white matter was related to substance use severity, mood, and impulsivity. Our findings suggest that ALC may benefit from interventions that facilitate normalization of DTI metrics to maintain abstinence, via smoking cessation, cognitive-based therapy, and perhaps pharmacology to support remyelination.

Alterations of resting state functional network connectivity in the brain of nicotine and alcohol users

Alcohol and nicotine intake result in neurological alterations at the circuit level. Resting state functional connectivity has shown great potential in identifying these alterations. However, current studies focus on specific seeds and leave out many brain regions where effects might exist. The present study uses a data driven technique for brain segmentation covering the whole brain. Functional magnetic-resonance-imaging (fMRI) data were collected from 188 subjects:51 non-substance consumption controls (CTR), 36 smoking-and-drinking subjects (SAD), 28 drinkers (DRN), and 73 smokers (SMK). Data were processed using group independent component analysis to derive resting state networks (RSN). The resting state functional network connectivity (rsFNC) was then calculated through correlation between time courses. One-way ANOVA tests were used to detect rsFNC differences among the four groups. A total of 50 ANOVA tests were significant after multi-comparison correction. Results delineate a general pattern of hypo-connectivity in the substance consumers. Precuneus, postcentral gyrus, insula and visual cortex were the main brain areas with rsFNC reduction suggesting reduced interoceptive awareness in drinkers. In addition, connectivity reduction between postcentral and one RSN covering right fusiform and lingual gyri showed significant association with severity of hazardous drinking. In smokers, connectivity changes agreed with the idea of a shift towards endogenous information processing, represented by the DMN. Hypo-connectivity between thalamus and putamen was observed in smokers. In contrast, the angular gyrus showed hyper-connectivity with the precuneus linked to smoking and significantly correlated with nicotine dependence severity. In spite of the presence of common effects, our results suggest that particular effects of alcohol and nicotine can be separated and identified. Results also suggest that concurrent use of both substances affects brain connectivity in a complex manner, requiring careful consideration of interaction effects.

Neuroimaging in alcohol-use disorders: clinical implications and future directions

Advances in clinical research have led to significant alterations in diagnostic criteria for alcohol-use disorders (AUD). Neuroimaging techniques are now being called upon to shed light on the validity and clinical utility of diagnostic criteria. For example, craving has recently been added to the diagnostic criteria of AUD based mainly on neurobiological research. In addition to understanding the nuances of the craving process, neuroimaging techniques are helping determine the biological factors that contribute to the onset and maintenance of the disorder and offer insight into the mechanisms underlying treatment. The purpose of this review is to provide a clinically relevant summary of the neuroimaging research that has impacted our understanding of the etiology, treatment and recovery in AUD.

Affected connectivity organization of the reward system structure in obesity

With the prevalence of obesity rapidly increasing worldwide, understanding the processes leading to excessive eating behavior becomes increasingly important. Considering the widely recognized crucial role of reward processes in food intake, we examined the white matter wiring and integrity of the anatomical reward network in obesity. Anatomical wiring of the reward network was reconstructed derived from diffusion weighted imaging in 31 obese participants and 32 normal-weight participants. Network wiring was compared in terms of the white matter volume as well as in terms of white matter microstructure, revealing lower number of streamlines and lower fiber integrity within the reward network in obese subjects. Specifically, the orbitofrontal cortex and striatum nuclei including accumbens, caudate and putamen showed lower strength and network clustering in the obesity group as compared to healthy controls. Our results provide evidence for obesity-related disruptions of global and local anatomical connectivity of the reward circuitry in regions that are key in the reinforcing mechanisms of eating-behavior processes.

The Network Modification (NeMo) Tool: elucidating the effect of white matter integrity changes on cortical and subcortical structural connectivity

Accurate prediction of brain dysfunction caused by disease or injury requires the quantification of resultant neural connectivity changes compared with the normal state. There are many methods with which to assess anatomical changes in structural or diffusion magnetic resonance imaging, but most overlook the topology of white matter (WM) connections that make up the healthy brain network. Here, a new neuroimaging software pipeline called the Network Modification (NeMo) Tool is presented that associates alterations in WM integrity with expected changes in neural connectivity between gray matter regions. The NeMo Tool uses a large reference set of healthy tractograms to assess implied network changes arising from a particular pattern of WM alteration on a region- and network-wise level. In this way, WM integrity changes can be extrapolated to the cortices and deep brain nuclei, enabling assessment of functional and cognitive alterations. Unlike current techniques that assess network dysfunction, the NeMo tool does not require tractography in pathological brains for which the algorithms may be unreliable or diffusion data are unavailable. The versatility of the NeMo Tool is demonstrated by applying it to data from patients with Alzheimer's disease, fronto-temporal dementia, normal pressure hydrocephalus, and mild traumatic brain injury. This tool fills a gap in the quantitative neuroimaging field by enabling an investigation of morphological and functional implications of changes in structural WM integrity.

Networks of anatomical covariance

Functional imaging or diffusion-weighted imaging techniques are widely used to understand brain connectivity at the systems level and its relation to normal neurodevelopment, cognition or brain disorders. It is also possible to extract information about brain connectivity from the covariance of morphological metrics derived from anatomical MRI. These covariance patterns may arise from genetic influences on normal development and aging, from mutual trophic reinforcement as well as from experience-related plasticity. This review describes the basic methodological strategies, the biological basis of the observed covariance as well as applications in normal brain and brain disease before a final review of future prospects for the technique.