Microstructural MRI Basis of the Cognitive Functions in Patients with Spinocerebellar Ataxia Type 2

Effective connectivity analysis of resting-state mentalizing brain networks in spinocerebellar ataxia type 2: A dynamic causal modeling study

Neuroimaging studies on healthy subjects described the causal effective connectivity of cerebellar-cerebral social mentalizing networks, revealing the presence of closed-loops. These studies estimated effective connectivity by applying Dynamic Causal Modeling on task-related fMRI data of healthy subjects performing mentalizing tasks. Thus far, few studies have applied Dynamic Causal Modeling to resting-state fMRI (rsfMRI) data to test the effective connectivity within the cerebellar-cerebral mentalizing network in the absence of experimental manipulations, and no study applied Dynamic Causal Modeling on fMRI data of patients with cerebellar disorders typically showing social cognition deficits. Thus, in this research we applied spectral Dynamic Causal Modeling, to rsfMRI data of 13 patients affected by spinocerebellar ataxia type 2 (SCA2) and of 23 matched healthy subjects. Specifically, effective connectivity was tested between acknowledged mentalizing regions of interest: bilateral cerebellar Crus II, dorsal and ventral medial prefrontal cortex, bilateral temporo-parietal junctions and precuneus. SCA2 and healthy subjects shared some similarities in cerebellar-cerebral mentalizing effective connectivity at rest, confirming the presence of closed-loops between cerebellar and cerebral mentalizing regions in both groups. However, relative to healthy subjects, SCA2 patients showed effective connectivity variations mostly in cerebellar-cerebral closed loops, namely weakened inhibitory connectivity from the cerebellum to the cerebral cortex, but stronger inhibitory connectivity from the cerebral cortex to the cerebellum. The present study demonstrated that effective connectivity changes affect a function-specific mentalizing network in SCA2 patients, allowing to deepen the direction and strength of the causal effective connectivity mechanisms driven by the cerebellar damage associated with SCA2.

Cognitive Decline and Mood Alterations in the Mouse Model of Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2) is a hereditary disorder, caused by an expansion of polyglutamine in the ataxin-2 protein. Although the mutant protein is expressed throughout all the cell and organ types, the cerebellum is primarily affected. The disease progression is mainly accompanied by a decline in motor functions. However, the disturbances in cognitive abilities and low mental state have also been reported in patients. Recent evidence suggests that the cerebellar functionality expands beyond the motor control. Thus, the cerebellum turned out to be involved into the language, verbal working, and spatial memory; executive functions such as working memory, planning, organizing, and strategy formation; and emotional processing. Here, we used the transgenic SCA2-58Q mice to evaluate their anxiety, cognitive functions, and mood alterations. The expression of the mutant ataxin-2 specifically in the cerebellar Purkinje cells (PCs) in SCA2-58Q mice allowed us to study the direct involvement of the cerebellum into the cognitive and affective control. We determined that SCA2-58Q mice exhibit anxiolytic behavior, decline in spatial memory, and a depressive-like state. Our results support the idea of cerebellar involvement in cognitive control and the handling of emotions.

White matter integrity assessment in spinocerebellar ataxia type 2 (SCA2) patients

AIM

To assess the burden of white matter (WM) damage in the cerebrum and cerebellum of spinocerebellar ataxia type 2 (SCA2) patients in an attempt to identify key regions affected by the neurodegenerative processes using diffusion tensor imaging (DTI).

MATERIALS AND METHODS

Nine SCA2 patients and 16 age-matched healthy controls were examined twice (SCA2 patients 3.6 ± 0.7 years and controls 3.3 ± 1.0 years apart) on the same 1.5 T scanner by acquiring T1-weighted and diffusion-weighted (b-value = 1,000 s/mm2) images. Using tract-based spatial statistics, DTI analysis on fractional anisotropy (FA), mean diffusivity (MD), axial (AD)/radial (RD) diffusivity was performed.

RESULTS

At baseline magnetic resonance imaging (MRI), FA was significantly decreased in SCA2 patients in the corticospinal tracts, inferior and superior cerebellar peduncles, middle cerebellar peduncles, cerebral peduncles, right superior and posterior corona radiata. RD was only significantly increased in SCA2 patients in the middle cerebellar peduncles. No significant AD and MD changes were observed. Tract-based spatial statistics (TBSS) analysis between SCA2 patients at baseline and at follow-up showed no significant changes in any of the DTI metrics.

CONCLUSIONS

DTI is a sensitive tool for following the progression of WM neurodegeneration and severity assessment in patients with SCA2. These findings add to a better understanding of the neurological underpinnings of the symptoms experienced by SCA2 patients.

Progressive white matter degeneration in patients with spinocerebellar ataxia type 2

PURPOSE

Spinocerebellar ataxia type 2 (SCA2) is a progressive neurodegenerative disorder characterized by cerebellar atrophy. However, studies to elucidate the longitudinal progression of the neuropathology are limited. We sought to identify brain macrostructural and microstructural alterations in patients with SCA2 using fixel-based analysis (FBA) to better understand its distribution patterns and progression.

METHODS

We enrolled 9 patients with SCA2 and 16 age- and gender-matched controls. Longitudinal clinical and imaging data were collected at baseline, and 3.5 years later. Fiber density (FD), fiber-bundle cross-section (FC), and a combination of FD and FC (FDC) were calculated. The paired t-test was used to examine longitudinal differences. The associations between fixel-based metrics and clinical variables were explored in SCA2 patients.

RESULTS

At baseline, patients with SCA2 displayed multiple white matter tracts with significantly decreased FD, FC, and FDC in the corticospinal tract, cerebellar peduncles, brainstem, corpus callosum, thalamus, striatum, and prefrontal cortex, compared to controls. Over time, many of these macrostructural and microstructural alterations progressed, manifesting lower FD, FC, and FDC in corticospinal tract, middle cerebellar peduncle, brainstem, striatum, fornix, and cingulum. No significant brain white matter alterations were found in the healthy controls over time. There was no association between the FBA-derived metrics and clinical variables in SCA2.

CONCLUSION

This study provides evidence of brain macrostructural and microstructural alterations and of progression over time in SCA2. The FBA-derived metrics may serve as potential biomarkers of SCA2 progression.

Structural and connectivity parameters reveal spared connectivity in young patients with non-progressive compared to slow-progressive cerebellar ataxia

Introduction

Within Pediatric Cerebellar Ataxias (PCAs), patients with non-progressive ataxia (NonP) surprisingly show postural motor behavior comparable to that of healthy controls, differently to slow-progressive ataxia patients (SlowP). This difference may depend on the building of compensatory strategies of the intact areas in NonP brain network.

Methods

Eleven PCAs patients were recruited: five with NonP and six with SlowP. We assessed volumetric and axonal bundles alterations with a multimodal approach to investigate whether eventual spared connectivity between basal ganglia and cerebellum explains the different postural motor behavior of NonP and SlowP patients.

Results

Cerebellar lobules were smaller in SlowP patients. NonP patients showed a lower number of streamlines in the cerebello-thalamo-cortical tracts but a generalized higher integrity of white matter tracts connecting the cortex and the basal ganglia with the cerebellum.

Discussion

This work reveals that the axonal bundles connecting the cerebellum with basal ganglia and cortex demonstrate a higher integrity in NonP patients. This evidence highlights the importance of the cerebellum-basal ganglia connectivity to explain the different postural motor behavior of NonP and SlowP patients and support the possible compensatory role of basal ganglia in patients with stable cerebellar malformation.

A chlorzoxazone-folic acid combination improves cognitive affective decline in SCA2-58Q mice

Spinocerebellar ataxia type 2 (SCA2) is a polyglutamine disorder caused by a pathological expansion of CAG repeats in ATXN2 gene. SCA2 is accompanied by cerebellar degeneration and progressive motor decline. Cerebellar Purkinje cells (PCs) seem to be primarily affected in this disorder. The majority of the ataxia research is focused on the motor decline observed in ataxic patients and animal models of the disease. However, recent evidence from patients and ataxic mice suggests that SCA2 can also share the symptoms of the cerebellar cognitive affective syndrome. We previously reported that SCA2-58Q PC-specific transgenic mice exhibit anxiolytic behavior, decline in spatial memory, and a depressive-like state. Here we studied the effect of the activation of the small conductance calcium-activated potassium channels (SK channels) by chlorzoxazone (CHZ) combined with the folic acid (FA) on the PC firing and also motor, cognitive and affective symptoms in SCA2-58Q mice. We realized that CHZ-FA combination improved motor and cognitive decline as well as ameliorated mood alterations in SCA2-58Q mice without affecting the firing rate of their cerebellar PCs. Our results support the idea of the combination therapy for both ataxia and non-motor symptoms in ataxic mice without affecting the firing frequency of PCs.

Cerebellum and Emotion in Social Behavior

Accumulating evidence suggests that the cerebellum plays a crucial role not only in the motor and cognitive domains but also in emotions and social behavior. In the present chapter, after a general introduction on the significance of the emotional components of social behavior, we describe recent efforts to understand the contributions of the cerebellum in social cognition focusing on the emotional and affective aspects. Specifically, starting from the description of the cerebello-cortical networks subtending the social-affective domains, we illustrate the most recent findings on the social cerebellum and the possible functional mechanisms by which the cerebellum modulate social-affective behavior. Finally, we discuss the possible consequences of cerebellar dysfunction in the social-affective domain, focusing on those neurological and psychopathological conditions in which emotional and social behavior difficulties have been described as being associated with cerebellar structural or functional alterations.

Cerebellar morphometric and spectroscopic biomarkers for Machado-Joseph Disease

Machado-Joseph disease (MJD) or Spinocerebellar ataxia type 3 (SCA3) is the most common form of dominant SCA worldwide. Magnetic Resonance Imaging (MRI) and Proton Magnetic Resonance Spectroscopy (¹H-MRS) provide promising non-invasive diagnostic and follow-up tools, also serving to evaluate therapies efficacy. However, pre-clinical studies showing relationship between MRI-MRS based biomarkers and functional performance are missing, which hampers an efficient clinical translation of therapeutics. This study assessed motor behaviour, neurochemical profiles, and morphometry of the cerebellum of MJD transgenic mice and patients aiming at establishing magnetic-resonance-based biomarkers. ¹H-MRS and structural MRI measurements of MJD transgenic mice were performed with a 9.4 Tesla scanner, correlated with motor performance on rotarod and compared with data collected from human patients. We found decreased cerebellar white and grey matter and enlargement of the fourth ventricle in both MJD mice and human patients as compared to controls. N-acetylaspartate (NAA), NAA + N-acetylaspartylglutamate (NAA + NAAG), Glutamate, and Taurine, were significantly decreased in MJD mouse cerebellum regardless of age, whereas myo-Inositol (Ins) was increased at early time-points. Lower neurochemical ratios levels (NAA/Ins and NAA/total Choline), previously correlated with worse clinical status in SCAs, were also observed in MJD mice cerebella. NAA, NAA + NAAG, Glutamate, and Taurine were also positively correlated with MJD mice motor performance. Importantly, these ¹H-MRS results were largely analogous to those found for MJD in human studies and in our pilot data in human patients. We have established a magnetic resonance-based biomarker approach to monitor novel therapies in preclinical studies and human clinical trials.

Cognitive impairment and its neuroimaging correlates in spinocerebellar ataxia 2

INTRODUCTION

Cognitive impairment (CI) is reported but is poorly explored in spinocerebellar ataxia 2 (SCA2). This study was undertaken to evaluate and classify cognitive impairment in patients with SCA2 and to identify their grey matter (GM) correlates.

METHODS

We evaluated the neurocognitive profile of 35 SCA2 and 30 age-, gender- and education-matched healthy controls using tests for attention, executive functions, learning and memory, language and fluency, and visuomotor constructive ability. Patients were classified into SCA2 with and without CI based on normative data from population and healthy controls. Furthermore, patients with CI were sub-classified based on the number of impaired domains into multi-domain CI (≥3 domains; MDCI) and limited domain CI (≤2 domains; LDCI). The underlying GM changes were identified using voxel based morphometry.

RESULTS

The mean age at onset, duration of disease, and ataxia score was 28.7 ± 8.51 years, 66.7 ± 44.1 months, and 16.1 ± 4.9 points, respectively. CI was present in 71.4% of SCA2 subjects (MDCI: 42.7%; LDCI: 28.5%). Patients with CI had significant atrophy of the posterior cerebellum, sensorimotor cortex, and superior frontal gyrus (FWE p-value <0.05). Patients with MDCI had significant GM atrophy of the angular gyrus compared to LDCI (FWE p-value <0.05).

CONCLUSION

Patients with CI had significant GM involvement of the posterior cerebellum and frontal lobe, suggestive of impairment in the cerebello-fronto-cortical circuitry.

The neurobiological underpinning of the social cognition impairments in patients with spinocerebellar ataxia type 2

Clinical studies described emotional and social behaviour alterations in patients with cerebellar diseases, proposing a role of specific cerebello-cerebral circuits in social cognition. However, for a long time these difficulties were underestimated, and no studies have addressed the correlation between social cognition deficits and topography of the cerebellar damage. The present study aims to investigate the social cognition impairment and the neuroanatomical alterations in patients with spinocerebellar ataxia type 2 (SCA2) and to analyze their relationship. To this purpose a social cognition battery composed by three tests, and a MRI protocol were administered to 13 SCA2 patients and 26 healthy subjects. The pattern of gray matter (GM) atrophy was analyzed by voxel-based morphometry, and the GM volumes of each altered area were correlated with the behavioral scores to investigate anatomo-functional relationships. In addition, we investigated the relationship between social deficits and damage to the cerebellar peduncles using DTI diffusivity indices. Our patients showed impairment of the immediate perceptual component of the mental state recognition (i.e., to recognize feelings and thoughts from the eyes expression), and difficulties in anger attribution, and in the understanding of false or mistaken beliefs. They showed a pattern of GM reduction in cerebellar regions, including lobules IX and VIIIb and Crus II, all of which are involved in specific components of the mentalizing process. Interestingly, the behavioral performance, in which SCA2 patients showed impairments compared to controls, correlated with the degree of cerebellar GM reduction and with the presence of microstructural abnormalities in the cerebellar peduncles. The present study provides the first characterization of the social cognition deficits in a homogenous cohort SCA2 patients and demonstrates that alterations in specific cerebellar regions should represent the neurobiological underpinning of their social behavior difficulties. Our results offer a new point of view in considering these aspects in the clinical practice.

Progression of Cerebellar Atrophy in Spinocerebellar Ataxia Type 2 Gene Carriers: A Longitudinal MRI Study in Preclinical and Early Disease Stages

Spinocerebellar ataxias type 2 (SCA2) is an autosomal dominant inherited disease caused by expanded trinucleotide repeats (≥32 CAG) within the coding region of ATXN2 gene. Age of disease onset primarily depends on the length of the expanded region. The majority of subjects carrying the mutation remain free of clinical signs for few decades (“pre-symptomatic” stage), but in proximity of disease onset subtle neurophysiological, cognitive, and structural brain imaging changes may occur. Aims of the present study are to determine the time-window in which early clinical and neurodegenerative MRI changes may be identified, and to evaluate the rate of the disease progression in both preclinical and early disease phases. We performed a 1-year longitudinal study in 42 subjects: 14 SCA2 patients (mean age 39 years, disease duration 7 years, SARA score 9 points), 13 presymptomatic SCA2 subjects (preSCA2, mean age 39 years, expected time to disease onset 16 years), and 15 gene-negative healthy controls (mean age 33 years). All participants underwent genetic test, neurological examination, cognitive tests, and brain MRI. Evaluations were repeated at 1-year interval. Baseline MRI evaluations in SCA2 patients showed significant atrophy in cerebellum, brainstem, basal ganglia and cortex compared to controls, while preSCA2 subjects had isolated volume loss in the pons, and cortical thinning in specific frontal and parietal areas, namely rostral-middle-frontal and precuneus. One-year longitudinal follow-up demonstrated, in SCA2 patients, volume reduction in cerebellum, pons, superior cerebellar peduncles, and midbrain, and only in the cerebellum in preSCA2 subjects. No progression in clinical or cognitive measures was observed in preSCA2 subjects. The rate of volume loss in the cerebellum and subcortical regions greatly differed between patients and preSCA2. In conclusion, our pilot study demonstrated that MRI measures are highly sensitive to identify longitudinal structural changes in SCA2 patients, and in preSCA2 up to a decade before expected disease onset. These findings may contribute in the understanding of early neurodegenerative processes and may be useful in future therapeutical trials.

Functional Changes of Mentalizing Network in SCA2 Patients: Novel Insights into Understanding the Social Cerebellum

In recent years, increasing evidence of the cerebellar role in social cognition has emerged. The cerebellum has been shown to modulate cortical activity of social brain regions serving as a regulator of function-specific mentalizing and mirroring processes. In particular, a mentalizing area in the posterior cerebellum, specifically Crus II, is preferentially recruited for more complex and abstract forms of social processing, together with mentalizing cerebral areas including the dorsal medial prefrontal cortex (dmPFC), the temporo-parietal junction (TPJ), and the precuneus. In the present study, the network-based statistics approach was used to assess functional connectivity (FC) differences within this mentalizing cerebello-cerebral network associated with a specific cerebellar damage. To this aim, patients affected by spinocerebellar ataxia type 2 (SCA2), a neurodegenerative disease specifically affecting regions of the cerebellar cortex, and age-matched healthy subjects have been enrolled. The dmPFC, left and right TPJ, the precuneus, and the cerebellar Crus II were used as regions of interest to construct the mentalizing network to be analyzed and evaluate pairwise functional relations between them. When compared with controls, SCA2 patients showed altered internodal connectivity between dmPFC, left (L-) and right (R-) TPJ, and right posterior cerebellar Crus II.The present results indicate that FC changes affect a function-specific mentalizing network in patients affected by cerebellar damage. In particular, they allow to better clarify functional alteration mechanisms driven by the cerebellar damage associated with SCA2 suggesting that selective cortico-cerebellar functional disconnections may underlie patients' social impairment in domain-specific complex and abstract forms of social functioning.

Cerebello-Cortical Alterations Linked to Cognitive and Social Problems in Patients With Spastic Paraplegia Type 7: A Preliminary Study

Spastic paraplegia type 7 (SPG7), which represents one of the most common forms of autosomal recessive spastic paraplegia (MIM#607259), often manifests with a complicated phenotype, characterized by progressive spastic ataxia with evidence of cerebellar atrophy on brain MRI. Recent studies have documented the presence of peculiar dentate nucleus hyperintensities on T2-weighted images and frontal executive dysfunction in neuropsychological tests in SPG7 patients. Therefore, we decided to assess whether any particular MRI pattern might be specifically associated with SPG7 mutations and possibly correlated with patients' cognitive profiles. For this purpose, we evaluated six SPG7 patients, studying the cerebello-cortical network by MRI voxel-based morphometry and functional connectivity techniques, compared to 30 healthy control subjects. In parallel, we investigated the cognitive and social functioning of the SPG7 patients. Our results document specific cognitive alterations in language, verbal memory, and executive function in addition to an impairment of social task and emotional functions. The MRI scans showed a diffuse symmetric reduction in the cerebellar gray matter of the right lobule V, right Crus I, and bilateral lobule VI, together with a cerebral gray matter reduction in the lingual gyrus, precuneus, thalamus, and superior frontal gyrus. The evidence of an over-connectivity pattern between both the right and left cerebellar dentate nuclei and specific cerebral regions (the lateral occipital cortex, precuneus, left supramarginal gyrus, and left superior parietal lobule) confirms the presence of cerebello-cortical dysregulation in different networks involved in cognition and social functioning in SPG7 patients.

Neuroimaging Biomarkers in SCA2 Gene Carriers

A variety of Magnetic Resonance (MR) and nuclear medicine (NM) techniques have been used in symptomatic and presymptomatic SCA2 gene carriers to explore, in vivo, the physiopathological biomarkers of the neurological dysfunctions characterizing the associated progressive disease that presents with a cerebellar syndrome, or less frequently, with a levodopa-responsive parkinsonian syndrome. Morphometry performed on T1-weighted images and diffusion MR imaging enable structural and microstructural evaluation of the brain in presymptomatic and symptomatic SCA2 gene carriers, in whom they show the typical pattern of olivopontocerebellar atrophy observed at neuropathological examination. Proton MR spectroscopy reveals, in the pons and cerebellum of SCA2 gene carriers, a more pronounced degree of abnormal neurochemical profile compared to other spinocerebellar ataxias with decreased NAA/Cr and Cho/Cr, increased mi/Cr ratios, and decreased NAA and increased mI concentrations. These neurochemical abnormalities are detectable also in presymtomatic gene carriers. Resting state functional MRI (rsfMRI) demonstrates decreased functional connectivity within the cerebellum and of the cerebellum with fronto-parietal cortices and basal ganglia in symptomatic SCA2 subjects. ¹⁸F-fluorodeoxyglucose Positron Emission Tomography (PET) shows a symmetric decrease of the glucose uptake in the cerebellar cortex, the dentate nucleus, the brainstem and the parahippocampal cortex. Single photon emission tomography and PET using several radiotracers have revealed almost symmetric nigrostriatal dopaminergic dysfunction irrespective of clinical signs of parkinsonism which are already present in presymtomatic gene carriers. Longitudinal small size studies have proven that morphometry and diffusion MR imaging can track neurodegeneration in SCA2, and hence serve as progression biomarkers. So far, such a capability has not been reported for proton MR spectroscopy, rsfMRI and NM techniques. A search for the best surrogate marker for future clinical trials represents the current challenge for the neuroimaging community.

The Cerebellar Cognitive Affective/Schmahmann Syndrome: a Task Force Paper

Sporadically advocated over the last two centuries, a cerebellar role in cognition and affect has been rigorously established in the past few decades. In the clinical domain, such progress is epitomized by the "cerebellar cognitive affective syndrome" ("CCAS") or "Schmahmann syndrome." Introduced in the late 1990s, CCAS reflects a constellation of cerebellar-induced sequelae, comprising deficits in executive function, visuospatial cognition, emotion-affect, and language, over and above speech. The CCAS thus offers excellent grounds to investigate the functional topography of the cerebellum, and, ultimately, illustrate the precise mechanisms by which the cerebellum modulates cognition and affect. The primary objective of this task force paper is thus to stimulate further research in this area. After providing an up-to-date overview of the fundamental findings on cerebellar neurocognition, the paper substantiates the concept of CCAS with recent evidence from different scientific angles, promotes awareness of the CCAS as a clinical entity, and examines our current insight into the therapeutic options available. The paper finally identifies topics of divergence and outstanding questions for further research.

Cerebellar dentate nucleus functional connectivity with cerebral cortex in Alzheimer's disease and memory: a seed-based approach

Alzheimer's disease (AD) is a chronic neurodegenerative disorder characterized by specific patterns of gray and white matter damage and cognitive/behavioral manifestations. The cerebellum has also been implicated in the pathophysiology of AD. Because the cerebellum is known to have strong functional connectivity (FC) with associative cerebral cortex regions, it is possible to hypothesize that it is incorporated into intrinsic FC networks relevant to cognitive manifestation of AD. In the present study, the cerebellar dentate nucleus, the largest cerebellar nucleus and the major output channel to the cerebral cortex, was chosen as the region of interest to test potential cerebellocerebral FC alterations and correlations with patients' memory impairment in a group of patients with AD. Compared to controls, patients with AD showed an increase in FC between the dentate nucleus and regions of the lateral temporal lobe. This study demonstrates that lower memory performances in AD may be related to altered FC within specific cerebellocortical functional modules, thus suggesting the cerebellar contribution to AD pathophysiology and typical memory dysfunctions.

Molecular Mechanisms and Therapeutics for Spinocerebellar Ataxia Type 2

The effective therapeutic treatment and the disease-modifying therapy for spinocerebellar ataxia type 2 (SCA2) (a progressive hereditary disease caused by an expansion of polyglutamine in the ataxin-2 protein) is not available yet. At present, only symptomatic treatment and methods of palliative care are prescribed to the patients. Many attempts were made to study the physiological, molecular, and biochemical changes in SCA2 patients and in a variety of the model systems to find new therapeutic targets for SCA2 treatment. A better understanding of the uncovered molecular mechanisms of the disease allowed the scientific community to develop strategies of potential therapy and helped to create some promising therapeutic approaches for SCA2 treatment. Recent progress in this field will be discussed in this review article.

The Cerebellar Cognitive Affective/Schmahmann Syndrome: a Task Force Paper

Sporadically advocated over the last two centuries, a cerebellar role in cognition and affect has been rigorously established in the past few decades. In the clinical domain, such progress is epitomized by the "cerebellar cognitive affective syndrome" ("CCAS") or "Schmahmann syndrome." Introduced in the late 1990s, CCAS reflects a constellation of cerebellar-induced sequelae, comprising deficits in executive function, visuospatial cognition, emotion-affect, and language, over and above speech. The CCAS thus offers excellent grounds to investigate the functional topography of the cerebellum, and, ultimately, illustrate the precise mechanisms by which the cerebellum modulates cognition and affect. The primary objective of this task force paper is thus to stimulate further research in this area. After providing an up-to-date overview of the fundamental findings on cerebellar neurocognition, the paper substantiates the concept of CCAS with recent evidence from different scientific angles, promotes awareness of the CCAS as a clinical entity, and examines our current insight into the therapeutic options available. The paper finally identifies topics of divergence and outstanding questions for further research.

Topological Disruption of Structural Brain Networks in Patients With Cognitive Impairment Following Cerebellar Infarction

Cerebellar lesions can lead to a series of cognitive and emotional disorders by influencing cerebral activity via cerebro-cerebellar loops. To explore changes in cognitive function and structural brain networks in patients with posterior cerebellar infarction, we conducted the current study using diffusion-weighted MRI (32 cerebellar infarction patients, 29 controls). Moreover, a series of neuropsychological tests were used to assess the subject's cognitive performance. We found cognitive impairment following cerebellar infarction involving multiple cognitive domains, including memory, executive functions, visuospatial abilities, processing speed and language functions, and brain topological abnormalities, including changes in clustering coefficients, shortest path lengths, global efficiency, local efficiencies, betweenness centrality and nodal efficiencies. Our results indicated that measures of local efficiency, mainly in the precuneus, cingulate gyrus and frontal-temporal cortex, were significantly reduced with posterior cerebellar infarction. At the same time, The correlation analysis suggested thatthe abnormal alterations in the right PCG, bilateral DCG, right PCUN may play a core role in the cognitive impairment following cerebellar infarctions. The differences in topological features of the structural brain networks within the cerebro-cerebellar circuits may provide a new approach to explore the pathophysiological mechanisms of cognitive impairment following cerebellar infarction.

The Theory and Neuroscience of Cerebellar Cognition

Cerebellar neuroscience has undergone a paradigm shift. The theories of the universal cerebellar transform and dysmetria of thought and the principles of organization of cerebral cortical connections, together with neuroanatomical, brain imaging, and clinical observations, have recontextualized the cerebellum as a critical node in the distributed neural circuits subserving behavior. The framework for cerebellar cognition stems from the identification of three cognitive representations in the posterior lobe, which are interconnected with cerebral association areas and distinct from the primary and secondary cerebellar sensorimotor representations linked with the spinal cord and cerebral motor areas. Lesions of the anterior lobe primary sensorimotor representations produce dysmetria of movement, the cerebellar motor syndrome. Lesions of the posterior lobe cognitive-emotional cerebellum produce dysmetria of thought and emotion, the cerebellar cognitive affective/Schmahmann syndrome. The notion that the cerebellum modulates thought and emotion in the same way that it modulates motor control advances the understanding of the mechanisms of cognition and opens new therapeutic opportunities in behavioral neurology and neuropsychiatry.

Neuroimaging Applications in Chronic Ataxias

Magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT) and positron emission tomography (PET) are the main instruments for neuroimaging investigation of patients with chronic ataxia. MRI has a predominant diagnostic role in the single patient, based on the visual detection of three patterns of atrophy, namely, spinal atrophy, cortical cerebellar atrophy and olivopontocerebellar atrophy, which correlate with the aetiologies of inherited or sporadic ataxia. In fact spinal atrophy is observed in Friedreich ataxia, cortical cerebellar atrophy in Ataxia Telangectasia, gluten ataxia and Sporadic Adult Onset Ataxia and olivopontocerebellar atrophy in Multiple System Atrophy cerebellar type. The 39 types of dominantly inherited spinocerebellar ataxias show either cortical cerebellar atrophy or olivopontocerebellar atrophy. T2 or T2* weighted MR images can contribute to the diagnosis by revealing abnormally increased or decreased signal with a characteristic distribution. These include symmetric T2 hyperintensity of the posterior and lateral columns of the cervical spinal cord in Friedreich ataxia, diffuse and symmetric hyperintensity of the cerebellar cortex in Infantile Neuro-Axonal Dystrophy, symmetric hyperintensity of the peridentate white matter in Cerebrotendineous Xanthomatosis, and symmetric hyperintensity of the middle cerebellar peduncles and peridentate white matter, cerebral white matter and corpus callosum in Fragile X Tremor Ataxia Syndrome. Abnormally decreased T2 or T2* signal can be observed with a multifocal distribution in Ataxia Telangectasia and with a symmetric distribution in the basal ganglia in Multiple System Atrophy. T2 signal hypointensity lining diffusely the outer surfaces of the brainstem, cerebellum and cerebrum enables diagnosis of superficial siderosis of the central nervous system. The diagnostic role of nuclear medicine techniques is smaller. SPECT and PET show decreased uptake of radiotracers investigating the nigrostriatal system in Multiple System Atrophy and in patients with Fragile X Tremor Ataxia Syndrome. Semiquantitative or quantitative MRI, SPECT and PET data describing structural, microstructural and functional changes of the cerebellum, brainstem, and spinal cord have been widely applied to investigate physiopathological changes in patients with chronic ataxias. Moreover they can track diseases progression with a greater sensitivity than clinical scales. So far, a few small-size and single center studies employed neuroimaging techniques as surrogate markers of treatment effects in chronic ataxias.

Voxel-based meta-analysis of gray and white matter volume abnormalities in spinocerebellar ataxia type 2

OBJECTIVE

To identify the consistent findings from the whole-brain voxel-based morphometry (VBM) studies on spinocerebellar ataxia type 2 (SCA2).

METHODS

The whole-brain VBM studies comparing SCA2 patients and healthy controls (HCs) were systematically searched in PubMed, Embase databases from January 2000 to June 2017. The coordinates with significant differences in gray matter (GM) and white matter (WM) between SCA2 patients and HCs were extracted separately from each cluster. A meta-analysis was performed using anisotropic effect size-based signed differential mapping (AES-SDM) software.

RESULTS

A total of five studies with 65 SCA2 patients and 124 HCs were included in the GM meta-analysis. Four of the five studies with 50 SCA2 patients and 109 HCs were included in the WM meta-analysis. Significant and consistent GM volume reductions were detected in bilateral cerebellar hemispheres, cerebellar vermis, the right fusiform gyrus, the right parahippocampal gyrus, and the right lingual gyrus. The WM volume reductions were observed in bilateral cerebellar hemispheres, cerebellar vermis, middle cerebellar peduncles, pons, and bilateral cortico-spinal projections. The findings of the study remained largely unchanged in jackknife sensitivity analysis.

CONCLUSIONS

The consistent findings from our meta-analysis showed that GM volume reductions in SCA2 patients were not limited in cerebellum while significant WM volume reductions widely existed in cerebellum and pyramidal system. The findings provide morphological basis for further studies on SCA2.

The cerebellar topography of attention sub-components in spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease characterized by a progressive cerebellar syndrome and multiple-domain cognitive impairments. The cerebellum is known to contribute to distinct functional networks related to higher-level functions. The aims of the present study were to investigate the different sub-components of attention and to analyse possible correlations between attention deficits and specific cerebellar regions in SCA2 patients. To this purpose, 11 SCA2 patients underwent an exhaustive attention battery that evaluated several attention sub-components. The SCA2 group performed below the normal range in tasks assessing selective attention, divided attention, and sustained attention, obtaining negative Z-scores. These results were confirmed by non-parametric Mann-Whitney U tests that showed significant differences between SCA2 and control subjects in the same sub-components of the attention battery, allowing us to speculate on cerebellar involvement when a high cognitive demand is required (i.e., multisensory integration, sequencing, prediction of events, and inhibition of inappropriate response behaviours). The voxel-based morphometry analysis showed a pattern of significantly reduced grey matter volume in specific cerebellar lobules. In particular, the SCA2 patients showed significant grey matter loss in bilateral regions of the anterior cerebellar hemisphere (IV) and in the posterior lobe (VI-IX) and posterior vermis (VI-IX). Statistical analysis found significant correlations between grey matter reductions in the VIIb/VIIIa cerebellar lobules and impairments in Sustained and Divided Attention tasks and between grey matter reduction in the vermal VI lobule and impairment in the Go/NoGo task. For the first time, the study demonstrated the involvement of specific cerebellar lobules in different sub-components of the attention domain, giving further support to the inclusion of the cerebellum within the attention network.

Structural Complexity of the Cerebellum and Cerebral Cortex is Reduced in Spinocerebellar Ataxia Type 2

BACKGROUND AND PURPOSE

Fractal dimension (FD) is an index of structural complexity of cortical gray matter (GM) and white matter (WM). Application of FD to pontocerebellar degeneration has revealed cerebellar changes. However, so far, possible concurrent cerebral changes and progression of changes in brain complexity have not been investigated.

METHODS

We computed FD of cerebellar and cerebral cortex and WM derived from longitudinal brain MRI of patients with spinocerebellar ataxia type 2 (SCA2), which is an inherited cause of pontocerebellar degeneration. Nine SCA2 patients and 16 age-matched healthy controls were examined twice (3.6 ± .7 and 3.3 ± 1.0 years apart, respectively) on the same 1.5T MR scanner with T1-weighted imaging. Cortical GM and WM of the cerebrum and cerebellum were segmented using FreeSurfer and FD of these segmentations were computed.

RESULTS

At baseline, FD values of cerebellar GM and WM were significantly (P < .001) lower in SCA2 patients (2.48 ± .04 for GM and 1.74 ± .09 for WM) than in controls (2.56 ± .02 for GM and 2.22 ± .19 for WM). Also, FD values of cerebral GM were significantly (P < .05) lower in SCA2 patients (2.39 ± .03) than in controls (2.43 ± .02). No significant differences were observed for FD of the cerebral WM. The rate of change of FD values was not significantly different between SCA2 patients and controls.

CONCLUSIONS

The structural complexity of the cerebellum and cerebral cortex is reduced in SCA2 patients. Fractal analysis seems not to be able to demonstrate progression of changes associated with degeneration in SCA2.

Structural cerebellar correlates of cognitive functions in spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease involving the cerebellum and characterized by a typical motor syndrome. In addition, the presence of cognitive impairment is now widely acknowledged as a feature of SCA2. Given the extensive connections between the cerebellum and associative cerebral areas, it is reasonable to hypothesize that cerebellar neurodegeneration associated with SCA2 may impact on the cerebellar modulation of the cerebral cortex, thus resulting in functional impairment. The aim of the present study was to investigate and quantitatively map the pattern of cerebellar gray matter (GM) atrophy due to SCA2 neurodegeneration and to correlate that with patients' cognitive performances. Cerebellar GM maps were extracted and compared between SCA2 patients (n = 9) and controls (n = 33) by using voxel-based morphometry. Furthermore, the relationship between cerebellar GM atrophy and neuropsychological scores of the patients was assessed. Specific cerebellar GM regions were found to be affected in patients. Additionally, GM loss in cognitive posterior lobules (VI, Crus I, Crus II, VIIB, IX) correlated with visuospatial, verbal memory and executive tasks, while additional correlations with motor anterior (V) and posterior (VIIIA, VIIIB) lobules were found for the tasks engaging motor and planning components. Our results provide evidence that the SCA2 neurodegenerative process affects the cerebellar cortex and that MRI indices of atrophy in different cerebellar subregions may account for the specificity of cognitive symptomatology observed in patients, as result of a cerebello-cerebral dysregulation.

The cerebellum from the fetus to the elderly: history, advances, and future challenges

The cerebellum is now at the forefront of research in neuroscience. This is not just a coincidence, occurring about 250 years after the first description of the human cerebellum. The cerebellum contains the majority of neurons in the central nervous system and it is heavily connected with almost all cortical and subcortical areas of the supratentorial region as well as with the brainstem and the spinal cord. Cerebellar circuits are embedded in large-scale networks contributing to motor control and neurocognition. From a phenotypic standpoint, damage to cerebellar lobules interconnected with the sensorimotor cortices leads to a cerebellar motor syndrome, whereas lesions of the posterolateral cerebellum cause cognitive and neuropsychiatric impairments which may or may not be subtle. This topographic rule is valid in children and adults. Midline posterior vermal lesions cause behavioral/affective dysregulation, especially in kids. The extent of the spectrum of human cerebellar disorders is increasingly recognized from the fetus to the elderly, with recognition of consequences for the quality of life and socioeconomic costs due to lifelong morbidity of many cerebellar ataxias/pathologies. The prolonged duration of human cerebellar development makes the cerebellum especially susceptible to developmental disruption, both genetic and nongenetic. This explains the current emphasis on the clarification of the developmental course and impact of the cerebellum. The understanding of how germinal matrix zones and migration of neurons and glial cells end in a highly organized and foliated human cerebellum is essential. This is greatly accelerated by inputs from rodent developmental studies, in particular because cerebellar anatomy is conserved across species. Still, numerous questions on human fetal development remain unanswered. Although both advanced neuroimaging and genetic studies are currently leading to a better definition and understanding of the multitude of cerebellar symptoms, there is a gap, with a great need to develop therapies aiming at first, protection of the cerebellum during development, and second, restoration of cerebellar function in children and in adults. Dynamic profiles of the compensatory processes from newborns to elderly require specific studies.