Altered brain mechanisms of emotion processing in pre-manifest Huntington's disease

Gray matter alterations in Huntington's disease: A meta-analysis of VBM neuroimaging studies

Increasing neuroimaging studies have attempted to identify biomarkers of Huntington's disease (HD) progression. Here, we conducted voxel-based meta-analyses of voxel-based morphometry (VBM) studies on HD to investigate the evolution of gray matter volume (GMV) alterations and explore the effects of genetic and clinical features on GMV changes. A systematic review was performed to identify the relevant studies. Meta-analyses of whole-brain VBM studies were performed to assess the regional GMV changes in all HD mutation carriers, in presymptomatic HD (pre-HD), and in symptomatic HD (sym-HD). A quantitative comparison was performed between pre-HD and sym-HD. Meta-regression analyses were used to explore the effects of genetic and clinical features on GMV changes. Twenty-eight studies were included, comparing a total of 1811 HD mutation carriers [including 1150 pre-HD and 560 sym-HD] and 969 healthy controls (HCs). Pre-HD showed decreased GMV in the bilateral caudate nuclei, putamen, insula, anterior cingulate/paracingulate gyri, middle temporal gyri, and left dorsolateral superior frontal gyrus compared with HCs. Compared with pre-HD, GMV decrease in sym-HD extended to the bilateral median cingulate/paracingulate gyri, Rolandic operculum and middle occipital gyri, left amygdala, and superior temporal gyrus. Meta-regression analyses found that age, mean lengths of CAG repeats, and disease burden were negatively associated with GMV atrophy of the bilateral caudate and right insula in all HD mutation carriers. This meta-analysis revealed the pattern of GMV changes from pre-HD to sym-HD, prompting the understanding of HD progression. The pattern of GMV changes may be biomarkers for disease progression in HD.

Disgust as a transdiagnostic index of mental illness: A narrative review of clinical populations

Disgust is a basic emotion of rejection, providing an ancestral defensive mechanism against illness. Based on research that documents altered experiences of disgust across several psychopathological conditions, we conducted a narrative review to address the hypothesis that altered disgust may serve as a transdiagnostic index of mental illness. Our synthesis of the literature from past decades suggests that, compared to healthy populations, patients with mental disorders exhibit abnormal processing of disgust in at least one of the analyzed dimensions. We also outline evidence of alterations in brain areas relevant to disgust processing, such as the insula and the interconnected limbic network. Overall, we provide preliminary support for the hypothesis that altered disgust processing may serve as a transdiagnostic index of mental illness.

Heightened emotion processing as a compensatory mechanism in persons with Alzheimer's disease: Psychological insights from the tri-network model

Social and emotional communication is an integral tenant of life quality and well-being. Aberrations in functional connectivity can alter social emotional behavior in numerous disease states, including dementia. This paper aims to review the major network changes observed in Alzheimer's disease, with a focus on the tri-network model. The central executive network, default mode network, and principally the salience network will be discussed as they relate to both pathology and compensatory behavioral manifestations in persons with dementia. The psychological and behavioral correlates of these network changes will be reviewed with the intent of increasing understanding about the conscious experience and communication modalities utilized by persons with dementia, the understanding of which may promote meaningful communication with care providers and loved ones. This paper further seeks to reframe social emotional communication methods used by persons with dementia by marrying current knowledge of neuroscience, psychology, and person-centered care. In this way, a perspective is offered that considers the heightened emotional states experienced by persons with dementia as a potential compensatory mechanism that may hold practical value under some circumstances. The many ways in which the brain adapts to physical and psychological changes, aging, and injury are still under exploration. Emotion processing may provide clinical insight into the subjective experience of dementia in this regard. Emotions, therefore, may serve to promote social bonds, provide an avenue for non-verbal communication, and act as a construct to maintain agency in persons who ultimately lose autonomy.

Behavioral features in child and adolescent huntingtin gene-mutation carriers

INTRODUCTION

We compared neuropsychiatric symptoms between child and adolescent huntingtin gene-mutation carriers and noncarriers. Given previous evidence of atypical striatal development in carriers, we also assessed the relationship between neuropsychiatric traits and striatal development.

METHODS

Participants between 6 and 18 years old were recruited from families affected by Huntington's disease and tested for the huntingtin gene expansion. Neuropsychiatric traits were assessed using the Pediatric Behavior Scale and the Behavior Rating Inventory of Executive Function. Striatal volumes were extracted from 3T neuro-anatomical images. Multivariable linear regression models were conducted to evaluate the impact of group (i.e., gene nonexpanded [GNE] or gene expanded [GE]), age, and trajectory of striatal growth on neuropsychiatric symptoms.

RESULTS

There were no group differences in any behavioral measure with the exception of depression/anxiety score, which was higher in the GNE group compared to the GE group (estimate = 4.58, t(129) = 2.52, FDR = 0.051). The growth trajectory of striatal volume predicted depression scores (estimate = 0.429, 95% CI 0.15:0.71, p = .0029), where a negative slope of striatal volume over time was associated with lower depression/anxiety.

CONCLUSIONS

The current findings show that GE children may have lower depression/anxiety compared to their peers. Previously, we observed a unique pattern of early striatal hypertrophy and continued decrement in volume over time among GE children and adolescents. In contrast, GNE individuals largely show striatal volume growth. These findings suggest that the lower scores of depression and anxiety seen in GE children and adolescents may be associated with differential growth of the striatum.

Tit for tat: costly punishment in manifest Huntington's disease

OBJECTIVE

We aimed to investigate costly punishment in patients with HD.

BACKGROUND

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease with motor, cognitive, and psychiatric symptoms. As neuropsychiatric abnormalities often precede motor symptoms, we wanted to assess whether costly punishment is part of the neuropsychological profile of patients with HD.

METHODS

A total of 40 non demented subjects were prospectively enrolled in this study with a between-subject design comparing manifest HD patients (n=18) to healthy controls (HC; n=22). All participants performed eight rounds of a costly punishment task, in which money was shared unevenly in 5 rounds or in a fair manner in the remaining three rounds. Participants then had to decide whether they wanted to punish the trustee. Furthermore, all participants underwent neuropsychological background tasks.

RESULTS

HD patients performed worse in the neuropsychological background tests compared to HC (all p-values<0.05). Moreover, HD patients punished more often in fair (Wald x2=5.03, p=0.025) but not in unfair rounds (Wald x2=1.63, p=0.202).

CONCLUSIONS

Our results demonstrate increased costly punishment during fair conditions in HD patients. Whether this behaviour is due to a lack of recognition of social norms, an impairment in top-down inhibition, or an effect of anti-dopaminergic medication remains unclear.

Cognitive and Affective Empathy in Huntington's Disease

BACKGROUND

Empathy is a multidimensional construct and a key component of social cognition. In Huntington's disease (HD), little is known regarding the phenomenology and the neural correlates of cognitive and affective empathy, and regarding how empathic deficits interact with other behavioral and cognitive manifestations.

OBJECTIVE

To explore the cognitive and affective empathy disturbances and related behavioral and neural correlates in HD.

METHODS

Clinical and sociodemographic data were obtained from 36 healthy controls (HC) and 54 gene-mutation carriers (17 premanifest and 37 early-manifest HD). The Test of Cognitive and Affective Empathy (TECA) was used to characterize cognitive (CE) and affective empathy (AE), and to explore their associations with grey matter volume (GMV) and cortical thickness (Cth).

RESULTS

Compared to HC, premanifest participants performed significantly worse in perspective taking (CE) and empathic distress (AE). In symptomatic participants, scores were significantly lower in almost all the TECA subscales. Several empathy subscales were associated with the severity of apathy, irritability, and cognitive deficits. CE was associated with GMV in thalamic, temporal, and occipital regions, and with Cth in parietal and temporal areas. AE was associated with GMV in the basal ganglia, limbic, occipital, and medial orbitofrontal regions, and with Cth in parieto-occipital areas.

CONCLUSION

Cognitive and affective empathy deficits are detectable early, are more severe in symptomatic participants, and involve the disruption of several fronto-temporal, parieto-occipital, basal ganglia, and limbic regions. These deficits are associated with disease severity and contribute to several behavioral symptoms, facilitating the presentation of maladaptive patterns of social interaction.

Problems with Social Cognition and Decision-Making in Huntington's Disease: Why Is it Important?

Huntington’s disease starts slowly and progresses over a 15–20 year period. Motor changes begin subtly, often going unnoticed by patients although they are typically visible to those close to them. At this point, it is the early non-motor problems of HD that arguably cause the most functional impairment. Approximately 65% of gene carriers will experience a reduction in their occupational level, and just under half will feel unable to manage their finances independently before a clinical diagnosis is made. Understanding what drives this impairment in activities of daily living is the key to helping people with HD to live more independently for longer, especially in early disease. Early cognitive decline is likely to play a contributory factor although few studies have looked directly at this relationship. Recently, it has been shown that along with the well documented dysexecutive syndrome seen in HD, changes in social cognition and decision-making are more common than previously thought. Furthermore, some of the early neuropathological and neurochemical changes seen in HD disrupt networks known to be involved in social functioning. In this review, we explore how HD changes the way individuals interact in a social world. Specifically, we summarise the literature on both classical and social decision-making (value-based decision-making in a social context) along with studies of theory of mind, empathy, alexithymia, and emotion recognition in HD. The literature specific to HD is discussed and supported by evidence from similar neurodegenerative disorders and healthy individuals to propose future directions and potential therapeutic avenues to be explored.

Altered third-party punishment in Huntington's disease: A study using neuroeconomic games

BACKGROUND

Huntington's disease (HD) is a heritable degenerative brain disease caused by a mutation in the huntingtin gene with excessive repeats of the base triplet cytosine-adenine-guanine (CAG), which codes for the aminoacid glutamine. HD is associated with a broad spectrum of neurocognitive dysfunction, including deficits in social cognition. The appreciation of fairness rules and reciprocity has not been studied in HD. Based on theoretical considerations suggesting that brain regions known to be affected from HD are involved in economic decision-making, the present study sought to examine HD patients' performance in two neuroeconomic games.

METHODS

Twenty-nine manifest HD mutation carriers (20 males, nine females) performed an Ultimatum Game (UG) and a Dictator Game (DG) where third-party punishment of observed unfairness was required. In addition, patients were tested for neurocognition and the ability to understand other people's mental states ("theory of mind"). For comparison, a clinical control group of 30 patients with chronic schizophrenia, and 30 unaffected healthy controls matched for age and verbal intelligence took part in the study.

RESULTS

Patients with HD had some appreciation of fairness rules, as they tended to reject unfair offers in the UG similar to controls. However, unlike the other two groups, individuals with HD did not punish observed unfairness from a third-party perspective. This lack of "altruistic punishment" was associated with deficits in executive functioning including working memory, inhibitory control and cognitive flexibility, and to a lesser degree with poor "theory of mind."

CONCLUSIONS

HD seems to be associated with impairments in understanding of more complex rules of social exchange. Aside from deficits in executive functioning, this behavior could, in part, be linked to an inability to experience third-party punishment as rewarding.

The Role of the Cerebellum in Huntington's Disease: a Systematic Review

Huntington's disease (HD) is a rare neurological disorder characterized by progressive motor, cognitive, and psychiatric disturbances. Although striatum degeneration might justify most of the motor symptoms, there is an emerging evidence of involvement of extra-striatal structures, such as the cerebellum. To elucidate the cerebellar involvement and its afferences with motor, psychiatric, and cognitive symptoms in HD. A systematic search in the literature was performed in MEDLINE, LILACS, and Google Scholar databases. The research was broadened to include the screening of reference lists of review articles for additional studies. Studies available in the English language, dating from 1993 through May 2020, were included. Clinical presentation of patients with HD may not be considered as the result of an isolated primary striatal dysfunction. There is evidence that cerebellar involvement is an early event in HD and may occur independently of striatal degeneration. Also, the loss of the compensation role of the cerebellum in HD may be an explanation for the clinical onset of HD. Although more studies are needed to elucidate this association, the current literature supports that the cerebellum may integrate the natural history of neurodegeneration in HD.

EEG based emotion recognition using minimum spanning tree

Emotion is a fundamental factor that influences human cognition, motivation, decision making and social interactions. This psychological state arises spontaneously and goes with physiological changes that can be recognized by computational methods. In this study, changes in minimum spanning tree (MST) structure of brain functional connectome were used for emotion classification based on EEG data and the obtained results were employed for interpretation about the most informative frequency content of emotional states. For estimation of interaction between different brain regions, several connectivity metrics were applied and interactions were calculated in different frequency bands. Subsequently, the MST graph was extracted from the functional connectivity matrix and its features were used for emotion recognition. The results showed that the accuracy of the proposed method for separating emotions with different arousal levels was 88.28%, while for different valence levels it was 81.25%. Interestingly, the system performance for binary classification of emotions based on quadrants of arousal-valence space was also higher than 80%. The MST approach allowed us to study the change of brain complexity and dynamics in various emotional states. This capability provided us enough knowledge to claim lower-alpha and gamma bands contain the main information for discrimination of emotional states.

Age-related alteration of emotional regulation in the BACHD rat model of Huntington disease

Huntington's disease (HD) is a genetic neurodegenerative disorder, caused by an expanded CAG repeat in the gene encoding the huntingtin protein. At the premanifest phase, before motor symptoms occur, psychiatric and emotional disorders are observed with high prevalence in HD patients. Agitation, anxiety and irritability are often described but also depression and/or apathy, associated with a lack of emotional control. The aim of the present study was to better circumscribe and understand the emotional symptoms and assess their evolution according to the progression of the disease using a transgenic HD model, BACHD rats, at the age of 4, 12 and 18 months. To achieve this goal, we confronted animals to two types of tests: first, tests assessing anxiety like the light/dark box and the conflict test, which are situations that did not involve an obvious threat and tests assessing the reactivity to a present threat using confrontation with an unknown conspecific (social behavior test) or with an aversive stimulus (fear conditioning test). In all animals, results show an age-dependent anxiety-like behavior, particularly marked in situation requiring passive responses (light/dark box and fear conditioning tests). BACHD rats exhibited a more profound alteration than WT animals in these tests from an early stage of the disease whereas, in tasks requiring some kind of motivation (for food or for social contacts), only old BACHD rats showed high anxiety-like behavior compared to WT, may be partly due to the other symptoms' occurrence at this stage: locomotor difficulties and/or apathy.

New Perspectives on Emotional Processing in People with Symptomatic Huntington's Disease: Impaired Emotion Regulation and Recognition of Emotional Body Language†

OBJECTIVE

Emotion regulation and emotional body language (EBL) recognition represent two fundamental components of emotional processing that have recently seen a considerable surge in research interest, in part due to the role they play in optimizing mental health. This appears to be particularly true for clinical conditions that can profoundly affect emotional functioning. Among these is Huntington's disease (HD), a neurodegenerative disorder that is associated with several psychological difficulties and cognitive impairments, including well-established deficits in facial emotion recognition. However, although the theoretical case for impairments is strong, the current evidence in HD on other components such as emotion regulation and EBL recognition is sparse.

METHOD

In this study, it was hypothesized that emotion regulation and recognition of EBL are impaired in people with symptomatic HD, and that these impairments significantly and positively correlate with each other. A between-subjects design was adopted to compare 13 people with symptomatic HD with 12 non-affected controls matched for age and education.

RESULTS

The results showed that emotion regulation and EBL recognition were significantly impaired in individuals with HD. Moreover, a significant positive correlation was observed between facial and EBL recognition impairments, whereas EBL performance was negatively related to the disease stage. However, emotion regulation and recognition performances were not significantly correlated.

CONCLUSIONS

This investigation represents the first evidence of a deficit of emotion regulation and EBL recognition in individuals with HD. The clinical implications of these findings are explored, and indications for future research are proposed.

Huntington's disease: Brain imaging in Huntington's disease

Huntington's disease (HD) gene-carriers show prominent neuronal loss by end-stage disease, and the use of magnetic resonance imaging (MRI) has been increasingly used to quantify brain changes during earlier stages of the disease. MRI offers an in vivo method of measuring structural and functional brain change. The images collected via MRI are processed to measure different anatomical features, such as brain volume, macro- and microstructural changes within white matter and functional brain activity. Structural imaging has demonstrated significant volume loss across multiple white and gray matter regions in HD, particularly within subcortical structures. There also appears to be increasing disorganization of white matter tracts and between-region connectivity with increasing disease progression. Finally, functional changes are thought to represent changes in brain activity underlying compensatory mechanisms in HD. This chapter will provide an overview of the principles of MRI and practicalities associated with using MRI in HD studies, and summarize findings from MRI studies investigating brain structure and function in HD.

Progressive microstructural changes of the occipital cortex in Huntington's disease

In this study we longitudinally investigated the rate of microstructural alterations in the occipital cortex in different stages of Huntington's disease (HD) by applying an automated atlas-based approach to diffusion MRI data. Twenty-two premanifest (preHD), 10 early manifest HD (early HD) and 24 healthy control subjects completed baseline and two year follow-up scans. The preHD group was stratified based on the predicted years to disease onset into a far (preHD-A) and near (preHD-B) to disease onset group. Clinical and behavioral measures were collected per assessment time point. An automated atlas-based DTI analysis approach was used to obtain the mean, axial and radial diffusivities of the occipital cortex. We found that the longitudinal rate of diffusivity change in the superior occipital gyrus (SOG), middle occipital gyrus (MOG), and inferior occipital gyrus (IOG) was significantly higher in early HD compared to both preHD and controls (all p's ≤ 0.005), which can be interpreted as an increased rate of microstructural degeneration. Furthermore, the change rate in the diffusivity of the MOG could significantly discriminate between preHD-B compared to preHD-A and the other groups (all p's ≤ 0.04). Finally, we found an inverse correlation between the Stroop Word Reading task and diffusivities in the SOG and MOG (all p's ≤ 0.01). These findings suggest that measures obtained from the occipital cortex can serve as sensitive longitudinal biomarkers for disease progression in preHD-B and early HD. These could in turn be used to assess potential effects of proposed disease modifying therapies.

Disease-Modification in Huntington's Disease: Moving Away from a Single-Target Approach

To date, no candidate intervention has demonstrated a disease-modifying effect in Huntington's disease, despite promising results in preclinical studies. In this commentary we discuss disease-modifying therapies that have been trialled in Huntington's disease and speculate that these failures may be attributed, in part, to the assumption that a single drug selectively targeting one aspect of disease pathology will be universally effective, regardless of disease stage or "subtype". We therefore propose an alternative approach for effective disease-modification that uses 1) a combination approach rather than monotherapy, and 2) targets the disease process early on - before it is clinically manifest. Finally, we will consider whether this change in approach that we propose will be relevant in the future given the recent shift to targeting more proximal disease processes-e.g., huntingtin gene expression; a timely question given Roche's recent decision to take on the clinical development of a promising new drug candidate in Huntington's disease, IONIS-HTTRx.

Functional Magnetic Resonance Imaging in Huntington's Disease

Huntington's disease is an inherited neurodegenerative condition characterized by motor dysfunction, cognitive impairment and neuropsychiatric disturbance. The effects of the underlying pathology on brain morphology are relatively well understood. Numerous structural Magnetic Resonance Imaging (MRI) studies have demonstrated macrostructural change with widespread striatal and cortical atrophy and microstructural white matter loss in premanifest and manifest HD gene carriers. However, disease effects on brain function are less well characterized. Functional MRI provides an opportunity to examine differences in brain activity either in response to a particular task or in the brain at rest. There is increasing evidence that HD gene carriers exhibit altered activation patterns and functional connectivity between brain regions in response to the neurodegenerative process. Here we review the growing literature in this area and critically evaluate the utility of this imaging modality.

Functional MRI signal fluctuations highlight altered resting brain activity in Huntington's disease

The fractional Amplitude of Low Frequency Fluctuations (fALFF) and the degree of local synchronization (Regional Homogeneity - ReHo) of resting-state BOLD signal have been suggested to map spontaneous neuronal activity and local functional connectivity, respectively. We compared voxelwise, independent of atrophy, the fALFF and ReHo patterns of 11 presymptomatic (ps-HD) and 28 symptomatic (sHD) Huntington's disease mutation carriers, with those of 40 normal volunteers, and tested their possible correlations with the motor and cognitive subscores of the Unified Huntington's Disease Rating Scale. In sHD patients, fALFF was mainly reduced bilaterally in parietal lobes (right precuneus being already affected in psHD), and in superior frontal gyri, and increased bilaterally in cerebellar lobules VI, VIII and IX, as well as in the right inferior temporal gyrus. In sHD, and to a lesser extent in psHD, ReHo was bilaterally reduced in putamina, cerebellar lobules III to VI, and superior medial frontal gyri, and increased in both psHD and sHD in fronto-basal cortices, and in the right temporal lobe. fALFF correlated inversely with cognitive scores in lobule IX of the cerebellum (mainly with total Stroop score, p < 0.0001), and in the medial portions of both thalami. These results are consistent with a reduced neuronal activity in the cortical components of the executive networks, known to be affected in Huntington's Disease, and with reduced local functional integration in subcortical and cerebellar components of the sensori-motor network. Cerebellar clusters of significant correlation of fALFF with executive function scores may be related to compensatory mechanisms.

Diminished facial EMG responses to disgusting scenes and happy and fearful faces in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder associated with impaired facial emotion recognition and altered subjective experience of emotion. These impairments likely result from the effects of the disease on underlying neurobiological mechanisms. Studies using self-report to examine emotional experiences have been ambiguous regarding whether experiences are diminished or exaggerated, possibly due to cognitive impairment and lack of insight in HD. To infer affective states more objectively and overcome the limitations of self-report, we used facial EMG to measure muscle responses to emotionally-evocative scenes. Further, we examined muscle responses to emotionally-expressive faces, because facial mimicry is thought to facilitate emotion recognition and social affiliation. Twenty-three HD participants (late pre-manifest and early symptomatic) were compared to twenty-five healthy controls in a scene condition and a face condition. EMG activity was measured from facial muscles associated with expressing particular emotions: 1) corrugator supercilii for anger, 2) frontalis for fear, 3) levator labii for disgust, and 4) both zygomaticus major and orbicularis oculi for happiness. Compared to controls, HD participants showed diminished responses to disgusting scenes, and to happy and fearful faces. Our findings provide evidence for a loss of disgust experience in HD. Further, consistent with the alleged affiliative function of facial mimicry, diminished mimicry responses may be relevant to social-emotional changes in HD. Our findings help understand the neural mechanisms underlying emotion processing impairments in HD.

The Alteration of Emotion Regulation Precedes the Deficits in Interval Timing in the BACHD Rat Model for Huntington Disease

Huntington disease (HD) is an autosomal dominantly inherited, progressive neurodegenerative disorder which is accompanied by executive dysfunctions and emotional alteration. The aim of the present study was to assess the impact of emotion/stress on on-going highly demanding cognitive tasks, i.e., temporal processing, as a function of age in BACHD rats (a “full length” model of HD). Middle-aged (4–6 months) and old (10–12 months) rats were first trained on a 2 vs. 8-s temporal discrimination task, and then exposed to a series of bisection tests under normal and stressful (10 mild unpredictable foot-shocks) conditions. The animals were then trained on a peak interval task, in which reinforced fixed-interval (FI) 30-s trials were randomly intermixed with non-reinforced probe trials. After training, the effect of stress upon time perception was again assessed. Sensitivity to foot-shocks was also assessed independently. The results show effects of both age and genotype, with largely greater effects in old BACHD animals. The older BACHD animals had impaired learning in both tasks, but reached equivalent levels of performance as WT animals at the end of training in the temporal discrimination task, while remaining impaired in the peak interval task. Whereas sensitivity to foot-shock did not differ between BACHD and WT rats, delivery of foot-shocks during the test sessions had a disruptive impact on temporal behavior in WT animals, an effect which increased with age. In contrast, BACHD rats, independent of age, did not show any significant disruption under stress. In conclusion, BACHD rats showed a disruption in temporal learning in late symptomatic animals. Age-related modification in stress-induced impairment of temporal control of behavior was also observed, an effect which was greatly reduced in BACHD animals, thus confirming previous results suggesting reduced emotional reactivity in HD animals. The results suggest a staggered onset in cognitive and emotional alterations in HD, with emotional alteration being the earliest, possibly related to different time courses of degeneration in cortico-striatal and amygdala circuits.

Whole-Brain Connectivity in a Large Study of Huntington's Disease Gene Mutation Carriers and Healthy Controls

Huntington's disease (HD) is an inherited brain disorder characterized by progressive motor, cognitive, and behavioral dysfunctions. It is caused by abnormally large trinucleotide cytosine-adenine-guanine (CAG) repeat expansions on exon 1 of the Huntingtin gene. CAG repeat length (CAG-RL) inversely correlates with an earlier age of onset. Region-based studies have shown that HD gene mutation carrier (HDgmc) individuals (CAG-RL ≥36) present functional connectivity alterations in subcortical (SC) and default mode networks. In this analysis, we expand on previous HD studies by investigating associations between CAG-RL and connectivity in the whole brain, as well as between CAG-dependent connectivity and motor and cognitive performances. We used group-independent component analysis on resting-state functional magnetic resonance imaging scans of 261 individuals (183 HDgmc and 78 healthy controls) from the PREDICT-HD study, to obtain whole-brain resting state networks (RSNs). Regression analysis was applied within and between RSNs connectivity (functional network connectivity [FNC]) to identify CAG-RL associations. Connectivity within the putamen RSN is negatively correlated with CAG-RL. The FNC between putamen and insula decreases with increasing CAG-RL, and also shows significant associations with motor and cognitive measures. The FNC between calcarine and middle frontal gyri increased with CAG-RL. In contrast, FNC in other visual (VIS) networks declined with increasing CAG-RL. In addition to observed effects in SC areas known to be related to HD, our study identifies a strong presence of alterations in VIS regions less commonly observed in previous reports and provides a step forward in understanding FNC dysfunction in HDgmc.

Stimulating neural plasticity with real-time fMRI neurofeedback in Huntington's disease: A proof of concept study

Novel methods that stimulate neuroplasticity are increasingly being studied to treat neurological and psychiatric conditions. We sought to determine whether real-time fMRI neurofeedback training is feasible in Huntington's disease (HD), and assess any factors that contribute to its effectiveness. In this proof-of-concept study, we used this technique to train 10 patients with HD to volitionally regulate the activity of their supplementary motor area (SMA). We collected detailed behavioral and neuroimaging data before and after training to examine changes of brain function and structure, and cognitive and motor performance. We found that patients overall learned to increase activity of the target region during training with variable effects on cognitive and motor behavior. Improved cognitive and motor performance after training predicted increases in pre-SMA grey matter volume, fMRI activity in the left putamen, and increased SMA-left putamen functional connectivity. Although we did not directly target the putamen and corticostriatal connectivity during neurofeedback training, our results suggest that training the SMA can lead to regulation of associated networks with beneficial effects in behavior. We conclude that neurofeedback training can induce plasticity in patients with Huntington's disease despite the presence of neurodegeneration, and the effects of training a single region may engage other regions and circuits implicated in disease pathology.

Early Detection of Apathetic Phenotypes in Huntington's Disease Knock-in Mice Using Open Source Tools

Apathy is one of the most prevalent and progressive psychiatric symptoms in Huntington's disease (HD) patients. However, preclinical work in HD mouse models tends to focus on molecular and motor, rather than affective, phenotypes. Measuring behavior in mice often produces noisy data and requires large cohorts to detect phenotypic rescue with appropriate power. The operant equipment necessary for measuring affective phenotypes is typically expensive, proprietary to commercial entities, and bulky which can render adequately sized mouse cohorts as cost-prohibitive. Thus, we describe here a home-built, open-source alternative to commercial hardware that is reliable, scalable, and reproducible. Using off-the-shelf hardware, we adapted and built several of the rodent operant buckets (ROBucket) to test Htt^Q111/+ mice for attention deficits in fixed ratio (FR) and progressive ratio (PR) tasks. We find that, despite normal performance in reward attainment in the FR task, Htt^Q111/+ mice exhibit reduced PR performance at 9-11 months of age, suggesting motivational deficits. We replicated this in two independent cohorts, demonstrating the reliability and utility of both the apathetic phenotype, and these ROBuckets, for preclinical HD studies.

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.

Social neuroscience: undoing the schism between neurology and psychiatry

Multiple disorders once jointly conceived as "nervous diseases" became segregated by the distinct institutional traditions forged in neurology and psychiatry. As a result, each field specialized in the study and treatment of a subset of such conditions. Here we propose new avenues for interdisciplinary interaction through a triangulation of both fields with social neuroscience. To this end, we review evidence from five relevant domains (facial emotion recognition, empathy, theory of mind, moral cognition, and social context assessment), highlighting their common disturbances across neurological and psychiatric conditions and discussing their multiple pathophysiological mechanisms. Our proposal is anchored in multidimensional evidence, including behavioral, neurocognitive, and genetic findings. From a clinical perspective, this work paves the way for dimensional and transdiagnostic approaches, new pharmacological treatments, and educational innovations rooted in a combined neuropsychiatric training. Research-wise, it fosters new models of the social brain and a novel platform to explore the interplay of cognitive and social functions. Finally, we identify new challenges for this synergistic framework.

Through your eyes or mine? The neural correlates of mental state recognition in Huntington's disease

Huntington's disease (HD) can impair social cognition. This study investigated whether patients with HD exhibit neural differences to healthy controls when they are considering mental and physical states relating to the static expressions of human eyes. Thirty-two patients with HD and 28 age-matched controls were scanned with fMRI during two versions of the Reading the Mind in the Eyes Task: The standard version requiring mental state judgments, and a comparison version requiring judgments about age. HD was associated with behavioral deficits on only the mental state eyes task. Contrasting the two versions of the eyes task (mental state > age judgment) revealed hypoactivation within left middle frontal gyrus and supramarginal gyrus in HD. Subgroup analyses comparing premanifest HD patients to age-matched controls revealed reduced activity in right supramarginal gyrus and increased activity in anterior cingulate during mental state recognition in these patients, while manifest HD was associated with hypoactivity in left insula and left supramarginal gyrus. When controlling for the effects of healthy aging, manifest patients exhibited declining activation within areas including right temporal pole. Our findings provide compelling evidence for a selective impairment of internal emotional status when patients with HD appraise facial features in order to make social judgements. Differential activity in temporal and anterior cingulate cortices may suggest that poor emotion regulation and emotional egocentricity underlie impaired mental state recognition in premanifest patients, while more extensive mental state recognition impairments in manifest disease reflect dysfunction in neural substrates underlying executive functions, and the experience and interpretation of emotion.

Neuroimaging in Dementia

Although the diagnosis of dementia still is primarily based on clinical criteria, neuroimaging is playing an increasingly important role. This is in large part due to advances in techniques that can assist with discriminating between different syndromes. Magnetic resonance imaging remains at the core of differential diagnosis, with specific patterns of cortical and subcortical changes having diagnostic significance. Recent developments in molecular PET imaging techniques have opened the door for not only antemortem but early, even preclinical, diagnosis of underlying pathology. This is vital, as treatment trials are underway for pharmacological agents with specific molecular targets, and numerous failed trials suggest that earlier treatment is needed. This article provides an overview of classic neuroimaging findings as well as new and cutting-edge research techniques that assist with clinical diagnosis of a range of dementia syndromes, with an emphasis on studies using pathologically proven cases.

Dissociation between decision-making under risk and decision-making under ambiguity in premanifest and manifest Huntington's disease

We investigated decision-making under ambiguity (DM-UA) and decision making under risk (DM-UR) in individuals with premanifest and manifest Huntington's disease (HD). Twenty individuals with premanifest HD and 23 individuals with manifest HD, on one hand, and 39 healthy individuals divided into two control groups, on the other, undertook a modified version of the Iowa Gambling Task (IGT), an adaptation of a DM-UA task, and a modified version of the Game of Dice Task (GDT), an adaptation of a DM-UR task. Participants also filled in a questionnaire of impulsivity and responded to cognitive tests specifically designed to assess executive functions. Compared to controls, individuals with premanifest HD were unimpaired in performing executive tests as well as in decision-making tasks, except for the Stroop task. In contrast, individuals with manifest HD were impaired in both the IGT and executive tasks, but not in the GDT. No sign of impulsivity was observed in individuals with premanifest or manifest HD. Our results suggest that the progression of HD impairs DM-UA without affecting DM-UR, and indicate that decision-making abilities are preserved during the premanifest stage of HD.

Neuroimaging as a tool to study the sources of phenotypic heterogeneity in Huntington's disease

PURPOSE OF REVIEW

Huntington's disease is a neurodegenerative disorder characterized by a triad of motor, cognitive and psychiatric disturbances. There is great variability regarding the prominence and evolution of each type of clinical sign. One possible source of phenotypic heterogeneity could be the more prominent degeneration of specific brain circuits. The scope of this review is to highlight the most recent neuroimaging studies that have analysed the relationship between brain changes and motor, cognitive and psychiatric alterations in Huntington's disease.

RECENT FINDINGS

The results from recent neuroimaging studies are heterogeneous. Although there is a great overlap between the different regions associated with each symptomatic domain, there is some degree of differentiation. For example, the motor network is associated with motor impairment, whereas the ventral striatum is especially involved in emotional deficits related with psychiatric problems.

SUMMARY

Motor, cognitive and psychiatric impairments are associated with structural and functional brain biomarkers. However, the specificity of the regions involved remains unknown, because these studies focused on specific regions and symptoms. In order to tease apart the neural substrates that underlie the phenotypic heterogeneity in Huntington's disease, multivariate approaches combining brain and behavioural measures related to all symptomatic domains should be considered in the future.

Social cognition in Huntington's disease: A meta-analysis

Neurocognitive impairment in Huntington's disease (HD) frequently includes deficits in emotion recognition, and recent studies have also provided evidence for deficits in theory of mind (ToM). There have been conflicting reports regarding the extent of emotion recognition and ToM deficits before the onset of motor symptoms in HD. In this meta-analysis, ToM and emotion recognition performances of 2226HD or pre-manifest HD and 998 healthy controls were included in the meta-analysis. Meta-regression analyses were conducted to investigate the relationship between social cognition deficits and demographic, cognitive and clinical features in HD. HD patients were significantly less accurate than controls in ToM and across all emotions in response to both facial and vocal stimuli. ToM (d=1.72) and recognition of negative emotions (d=1.20-1.33), especially anger, disgust and fear (d=1.26-1.52) were severely impaired. Pre-manifest HD was also associated with impairment in social cognition. The severity of emotion recognition impairment was significantly associated with disease burden, proximity of onset of motor symptoms and cognitive impairment. Social cognition impairments are potential biomarkers of disease onset and progression in HD.

Theory of mind and empathy in preclinical and clinical Huntington's disease

We investigated cognitive and affective Theory of Mind (ToM) and empathy in patients with premanifest and manifest Huntington's disease (HD). The relationship between ToM performance and executive skills was also examined. Sixteen preclinical and 23 clinical HD patients, and 39 healthy subjects divided into 2 control groups were given a French adaptation of the Yoni test (Shamay-Tsoory, S.G., Aharon-Peretz, J. (2007). Dissociable prefrontal networks for cognitive and affective theory of mind: a lesion study. Neuropsychologia, 45(3), 3054-67) that examines first- and second-order cognitive and affective ToM processing in separate conditions with a physical control condition. Participants were also given questionnaires of empathy and cognitive tests which mainly assessed executive functions (inhibition and mental flexibility). Clinical HD patients made significantly more errors than their controls in the first- and second-order cognitive and affective ToM conditions of the Yoni task, but exhibited no empathy deficits. However, there was no evidence that ToM impairment was related to cognitive deficits in these patients. Preclinical HD patients were unimpaired in ToM tasks and empathy measures compared with their controls. Our results are consistent with the idea that impaired affective and cognitive mentalizing emerges with the clinical manifestation of HD, but is not necessarily part of the preclinical stage. Furthermore, these impairments appear independent of executive dysfunction and empathy.

Selective vulnerability of Rich Club brain regions is an organizational principle of structural connectivity loss in Huntington's disease

Huntington's disease can be predicted many years before symptom onset, and thus makes an ideal model for studying the earliest mechanisms of neurodegeneration. Diffuse patterns of structural connectivity loss occur in the basal ganglia and cortex early in the disease. However, the organizational principles that underlie these changes are unclear. By understanding such principles we can gain insight into the link between the cellular pathology caused by mutant huntingtin and its downstream effect at the macroscopic level. The 'rich club' is a pattern of organization established in healthy human brains, where specific hub 'rich club' brain regions are more highly connected to each other than other brain regions. We hypothesized that selective loss of rich club connectivity might represent an organizing principle underlying the distributed pattern of structural connectivity loss seen in Huntington's disease. To test this hypothesis we performed diffusion tractography and graph theoretical analysis in a pseudo-longitudinal study of 50 premanifest and 38 manifest Huntington's disease participants compared with 47 healthy controls. Consistent with our hypothesis we found that structural connectivity loss selectively affected rich club brain regions in premanifest and manifest Huntington's disease participants compared with controls. We found progressive network changes across controls, premanifest Huntington's disease and manifest Huntington's disease characterized by increased network segregation in the premanifest stage and loss of network integration in manifest disease. These regional and whole brain network differences were highly correlated with cognitive and motor deficits suggesting they have pathophysiological relevance. We also observed greater reductions in the connectivity of brain regions that have higher network traffic and lower clustering of neighbouring regions. This provides a potential mechanism that results in a characteristic pattern of structural connectivity loss targeting highly connected brain regions with high network traffic and low clustering of neighbouring regions. Our findings highlight the role of the rich club as a substrate for the structural connectivity loss seen in Huntington's disease and have broader implications for understanding the connection between molecular and systems level pathology in neurodegenerative disease.

Reduced impact of emotion on choice behavior in presymptomatic BACHD rats, a transgenic rodent model for Huntington Disease

Executive dysfunction and psychiatric symptoms are hallmarks of Huntington disease (HD), a neurodegenerative disorder genetically characterized by expanded CAG repeats in the HTT gene. Using the BACHD rat model of HD (97 CAG-CAA repeats), the present research seeks to characterize the progressive emergence of decision-making impairments in a rat version of the Iowa Gambling Task (RGT) and the impact of emotional modulation, whether positive or negative, on choice behavior. The choice efficiency shown both by WT rats (independent of their age) and the youngest BACHD rats (2 and 8months old) evidenced that they are able to integrate outcomes of past decisions to determine expected reward values for each option. However, 18months old BACHD rats made fewer choices during the RGT session and were less efficient in choosing advantageous options than younger animals. Presenting either chocolate pellets or electrical footshocks half-way through a second RGT session reduced exploratory activity (inefficient nose-poking) and choices with a weaker effect on BACHD animals than on WT. Choice efficiency was left intact in transgenic rats. Our results bring new knowledge on executive impairments and impact of emotional state on decision-making at different stages of the disease, increasing the face-validity of the BACHD rat model.

Compensation in Preclinical Huntington's Disease: Evidence From the Track-On HD Study

BACKGROUND

Cognitive and motor task performance in premanifest Huntington's disease (HD) gene-carriers is often within normal ranges prior to clinical diagnosis, despite loss of brain volume in regions involved in these tasks. This indicates ongoing compensation, with the brain maintaining function in the presence of neuronal loss. However, thus far, compensatory processes in HD have not been modeled explicitly. Using a new model, which incorporates individual variability related to structural change and behavior, we sought to identify functional correlates of compensation in premanifest-HD gene-carriers.

METHODS

We investigated the modulatory effects of regional brain atrophy, indexed by structural measures of disease load, on the relationship between performance and brain activity (or connectivity) using task-based and resting-state functional MRI.

FINDINGS

Consistent with compensation, as atrophy increased performance-related activity increased in the right parietal cortex during a working memory task. Similarly, increased functional coupling between the right dorsolateral prefrontal cortex and a left hemisphere network in the resting-state predicted better cognitive performance as atrophy increased. Such patterns were not detectable for the left hemisphere or for motor tasks.

INTERPRETATION

Our findings provide evidence for active compensatory processes in premanifest-HD for cognitive demands and suggest a higher vulnerability of the left hemisphere to the effects of regional atrophy.

[Ophthalmic manifestations of Huntington's disease]

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin gene. The whole nervous system, including visual analyzer, is involved in the pathogenesis of the disease. Various ocular sings can be found in both preclinical and clinical stages of HD. Specific retinal damage, namely, abnormal proteins formation, photoreceptor degeneration and retinal remodeling, has been studied in animal models. Functional changes in occipital lobe activity and its atrophy as well as degeneration of visual pathways can already be present in the early stages of the disease. Oculomotor symptoms of HD include disturbed visual fixation, slower tracking eye movements and saccades, and suppressed vestibulo-ocular reflex. Visual perceptual disorders, such as visuospatial difficulties, problems of stimulus identification and motion perception, along with decreased contrast sensitivity, have also been described. The possibility of using certain ophthalmic parameters as biomarkers of HD is being discussed.

Interaction without intent: the shape of the social world in Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative condition. Patients with this movement disorder can exhibit deficits on tasks involving Theory of Mind (ToM): the ability to understand mental states such as beliefs and emotions. We investigated mental state inference in HD in response to ambiguous animations involving geometric shapes, while exploring the impact of symptoms within cognitive, emotional and motor domains. Forty patients with HD and twenty healthy controls described the events in videos showing random movements of two triangles (i.e. floating), simple interactions (e.g. following) and more complex interactions prompting the inference of mental states (e.g. one triangle encouraging the other). Relationships were explored between animation interpretation and measures of executive functioning, alexithymia and motor symptoms. Individuals with HD exhibited alexithymia and a reduced tendency to spontaneously attribute intentions to interacting triangles on the animations task. Attribution of intentions on the animations task correlated with motor symptoms and burden of pathology. Importantly, patients without motor symptoms showed similar ToM deficits despite intact executive functions. Subtle changes in ToM that are unrelated to executive dysfunction could therefore feature in basal ganglia disorders prior to motor onset.

Emotional dysfunctions in neurodegenerative diseases

Neurodegenerative diseases are characterized primarily by motor signs but are also accompanied by emotional disturbances. Because of the limited knowledge about these dysfunctions, this Review provides an overview of emotional competencies in Huntington's disease (HD), Parkinson's disease (PD), and multiple sclerosis (MS), with a focus on emotion recognition, emotion regulation, and depression. Most studies indicate facial emotion recognition deficits in HD and PD, whereas data for MS are inconsistent. On a neural level, dysfunctions of amygdala and striatum, among others, have been linked to these impairments. These dysfunctions also tap brain regions that are part of the emotion regulation network, suggesting problems in this competency, too. Research points to dysfunctional emotion regulation in MS, whereas findings for PD and HD are missing. The high prevalence of depression in all three disorders emphasizes the need for effective therapies. Research on emotional disturbances might improve treatment, thereby increasing patients' and caregivers' well-being.

The role of the amygdala during emotional processing in Huntington's disease: from pre-manifest to late stage disease

BACKGROUND

Deficits in emotional processing can be detected in the pre-manifest stage of Huntington's disease and negative emotion recognition has been identified as a predictor of clinical diagnosis. The underlying neuropathological correlates of such deficits are typically established using correlative structural MRI studies. This approach does not take into consideration the impact of disruption to the complex interactions between multiple brain circuits on emotional processing. Therefore, exploration of the neural substrates of emotional processing in pre-manifest HD using fMRI connectivity analysis may be a useful way of evaluating the way brain regions interrelate in the period prior to diagnosis.

METHODS

We investigated the impact of predicted time to disease onset on brain activation when participants were exposed to pictures of faces with angry and neutral expressions, in 20 pre-manifest HD gene carriers and 23 healthy controls. On the basis of the results of this initial study went on to look at amygdala dependent cognitive performance in 79 Huntington's disease patients from a cross-section of disease stages (pre-manifest to late disease) and 26 healthy controls, using a validated theory of mind task: "the Reading the Mind in the Eyes Test" which has been previously been shown to be amygdala dependent.

RESULTS

Psychophysiological interaction analysis identified reduced connectivity between the left amygdala and right fusiform facial area in pre-manifest HD gene carriers compared to controls when viewing angry compared to neutral faces. Change in PPI connectivity scores correlated with predicted time to disease onset (r=0.45, p<0.05). Furthermore, performance on the "Reading the Mind in the Eyes Test" correlated negatively with proximity to disease onset and became progressively worse with each stage of disease.

CONCLUSION

Abnormalities in the neural networks underlying social cognition and emotional processing can be detected prior to clinical diagnosis in Huntington's disease. Connectivity between the amygdala and other brain regions is impacted by the disease process in pre-manifest HD and may therefore be a useful way of identifying participants who are approaching a clinical diagnosis. Furthermore, the "Reading the Mind in the Eyes Test" is a surrogate measure of amygdala function that is clinically useful across the entire cross-section of disease stages in HD.

Functional connectivity modeling of consistent cortico-striatal degeneration in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by a complex neuropsychiatric phenotype. In a recent meta-analysis we identified core regions of consistent neurodegeneration in premanifest HD in the striatum and middle occipital gyrus (MOG). For early manifest HD convergent evidence of atrophy was most prominent in the striatum, motor cortex (M1) and inferior frontal junction (IFJ). The aim of the present study was to functionally characterize this topography of brain atrophy and to investigate differential connectivity patterns formed by consistent cortico-striatal atrophy regions in HD. Using areas of striatal and cortical atrophy at different disease stages as seeds, we performed task-free resting-state and task-based meta-analytic connectivity modeling (MACM). MACM utilizes the large data source of the BrainMap database and identifies significant areas of above-chance co-activation with the seed-region via the activation-likelihood-estimation approach. In order to delineate functional networks formed by cortical as well as striatal atrophy regions we computed the conjunction between the co-activation profiles of striatal and cortical seeds in the premanifest and manifest stages of HD, respectively. Functional characterization of the seeds was obtained using the behavioral meta-data of BrainMap. Cortico-striatal atrophy seeds of the premanifest stage of HD showed common co-activation with a rather cognitive network including the striatum, anterior insula, lateral prefrontal, premotor, supplementary motor and parietal regions. A similar but more pronounced co-activation pattern, additionally including the medial prefrontal cortex and thalamic nuclei was found with striatal and IFJ seeds at the manifest HD stage. The striatum and M1 were functionally connected mainly to premotor and sensorimotor areas, posterior insula, putamen and thalamus. Behavioral characterization of the seeds confirmed that experiments activating the MOG or IFJ in conjunction with the striatum were associated with cognitive functions, while the network formed by M1 and the striatum was driven by motor-related tasks. Thus, based on morphological changes in HD, we identified functionally distinct cortico-striatal networks resembling a cognitive and motor loop, which may be prone to early disruptions in different stages of the disease and underlie HD-related cognitive and motor symptom profiles. Our findings provide an important link between morphometrically defined seed-regions and corresponding functional circuits highlighting the functional and ensuing clinical relevance of structural damage in HD.

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Pre-HD atrophy seeds showed common functional co-activation with a cognitive network.

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Modeling of manifest-HD seeds delineated a segregation of a cognitive and motor loop.

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Behavioral decoding of atrophy seeds confirmed functional segregation of networks.

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Based on morphometric changes in HD distinct corticostriatal networks were identified.

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Findings depict functional and ensuing clinical relevance of structural damage in HD.

Basal ganglia-cortical structural connectivity in Huntington's disease

Huntington's disease is an incurable neurodegenerative disease caused by inheritance of an expanded cytosine-adenine-guanine (CAG) trinucleotide repeat within the Huntingtin gene. Extensive volume loss and altered diffusion metrics in the basal ganglia, cortex and white matter are seen when patients with Huntington's disease (HD) undergo structural imaging, suggesting that changes in basal ganglia-cortical structural connectivity occur. The aims of this study were to characterise altered patterns of basal ganglia-cortical structural connectivity with high anatomical precision in premanifest and early manifest HD, and to identify associations between structural connectivity and genetic or clinical markers of HD. 3-Tesla diffusion tensor magnetic resonance images were acquired from 14 early manifest HD subjects, 17 premanifest HD subjects and 18 controls. Voxel-based analyses of probabilistic tractography were used to quantify basal ganglia-cortical structural connections. Canonical variate analysis was used to demonstrate disease-associated patterns of altered connectivity and to test for associations between connectivity and genetic and clinical markers of HD; this is the first study in which such analyses have been used. Widespread changes were seen in basal ganglia-cortical structural connectivity in early manifest HD subjects; this has relevance for development of therapies targeting the striatum. Premanifest HD subjects had a pattern of connectivity more similar to that of controls, suggesting progressive change in connections over time. Associations between structural connectivity patterns and motor and cognitive markers of disease severity were present in early manifest subjects. Our data suggest the clinical phenotype in manifest HD may be at least partly a result of altered connectivity.

Mouse Models of Huntington's Disease

In this review, we explore the similarities and differences in the behavioural neurobiology found in the mouse models of Huntington's disease (HD) and the human disease state. The review is organised with a comparative focus on the functional domains of motor control, cognition and behavioural disturbance (akin to psychiatric disturbance in people) and how our knowledge of the underlying physiological changes that are manifest in the HD mouse lines correspond to those seen in the HD clinical population. The review is framed in terms of functional circuitry and neurotransmitter systems and how abnormalities in these systems impact on the behavioural readouts across the mouse lines and how these may correspond to the deficits observed in people. In addition, interpretational issues associated with the data from animal studies are discussed.

Movement disorders and psychiatry: Five new things

In this article we report recent interesting diagnostic and therapeutic advances in a diverse range of movement disorders with associated psychiatric comorbidity. Areas discussed include social cognition in Huntington disease, neuroimaging of functional movement disorders, treatment of psychosis in Parkinson disease, new advances in autoimmune disease, and management of Tourette syndrome.