Comparison of Cerebellar Grey Matter Alterations in Bipolar and Cerebellar Patients: Evidence from Voxel-Based Analysis

Case report and systematic review of cerebellar vermis alterations in psychosis

INTRODUCTION

Cerebellar alterations, including both volumetric changes in the cerebellar vermis and dysfunctions of the corticocerebellar connections, have been documented in psychotic disorders. Starting from the clinical observation of a bipolar patient with cerebellar hypoplasia, the purpose of this review is to summarize the data in the literature about the association between hypoplasia of the cerebellar vermis and psychotic disorders [schizophrenia (SCZ) and bipolar disorder (BD)].

METHODS

A bibliographic search on PubMed has been conducted, and 18 articles were finally included in the review: five used patients with BD, 12 patients with SCZ and one subject at psychotic risk.

RESULTS

For SCZ patients and subjects at psychotic risk, the results of most of the reviewed studies seem to suggest a gray matter volume reduction coupled with an increase in white matter volumes in the cerebellar vermis, compared to healthy controls. Instead, the results of the studies on BD patients are more heterogeneous with evidence showing a reduction, no difference or even an increase in cerebellar vermis volume compared to healthy controls.

CONCLUSIONS

From the results of the reviewed studies, a possible correlation emerged between cerebellar vermis hypoplasia and psychotic disorders, especially SCZ, ultimately supporting the hypothesis of psychotic disorders as neurodevelopmental disorders.

Role of the Cerebellum in Bipolar Disorder: A Systematic Literature Review

The aim of this systematic literature review was to investigate the role of the cerebellum in the affective symptoms observed in patients with bipolar disorder. The present systematic literature review included clinical studies conducted from 2013-2023 among adult populations with bipolar I and II disorders, along with their specifiers. With regard to cerebellar pathology, it was found that those with bipolar disorder performed worse than their healthy counterparts in their ability to comprehend the mental states of others and in identifying negative mental states. Additionally, individuals with bipolar disorder had reduced gray matter loss in regions such as lobules I-IX, crus I, and crus II, different functional activation patterns of the thalamus, striatum, and hippocampus on functional magnetic resonance imaging (fMRI), and increased cortical thickness. Cerebro-cerebellar functional connectivities were altered in patients with bipolar disorder. The effects of lamotrigine and lithium on cerebellar volume and abnormalities are also discussed in this paper. The present systematic literature review illustrates the emerging involvement of the cerebellum in bipolar disorder and its affective symptoms and paves the way for future research and a better understanding of bipolar disorder.

Decreased dynamic variability of the cerebellum in the euthymic patients with bipolar disorder

BACKGROUND

Bipolar disorder (BD) is a complex mental illness characterized by different mood states, including depression, mania/hypomania, and euthymia. This study aimed to comprehensively evaluate dynamic changes in intrinsic brain activity by using dynamic fractional amplitude of low-frequency fluctuations (dfALFF) and dynamic degree centrality (dDC) in patients with BD euthymia or depression and healthy individuals.

METHODS

The resting-state functional magnetic resonance imaging data were analyzed from 37 euthymic and 28 depressed patients with BD, as well as 85 healthy individuals. Using the sliding-window method, the dfALFF and dDC were calculated for each participant. These values were compared between the 3 groups using one-way analysis of variance (ANOVA). Additional analyses were conducted using different window lengths, step width, and window type to ensure the reliability of the results.

RESULTS

The euthymic group showed significantly lower dfALFF and dDC values of the left and right cerebellum posterior lobe compared with the depressed and control groups (cluster level PFWE < 0.05), while the latter two groups were comparable. Brain regions showing significant group differences in the dfALFF analysis overlapped with those with significant differences in the dDC analysis. These results were consistent across different window lengths, step width, and window type.

CONCLUSIONS

These findings suggested that patients with euthymic BD exhibit less flexibility of temporal functional activities in the cerebellum posterior lobes compared to either depressed patients or healthy individuals. These results could contribute to the development of neuropathological models of BD, ultimately leading to improved diagnosis and treatment of this complex illness.

Cerebellar Neurostimulation for Boosting Social and Affective Functions: Implications for the Rehabilitation of Hereditary Ataxia Patients

Beyond motor deficits, spinocerebellar ataxia (SCA) patients also suffer cognitive decline and show socio-affective difficulties, negatively impacting on their social functioning. The possibility to modulate cerebello-cerebral networks involved in social cognition through cerebellar neurostimulation has opened up potential therapeutic applications for ameliorating social and affective difficulties. The present review offers an overview of the research on cerebellar neurostimulation for the modulation of socio-affective functions in both healthy individuals and different clinical populations, published in the time period 2000-2022. A total of 25 records reporting either transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) studies were found. The investigated clinical populations comprised different pathological conditions, including but not limited to SCA syndromes. The reviewed evidence supports that cerebellar neurostimulation is effective in improving social abilities in healthy individuals and reducing social and affective symptoms in different neurological and psychiatric populations associated with cerebellar damage or with impairments in functions that involve the cerebellum. These findings encourage to further explore the rehabilitative effects of cerebellar neurostimulation on socio-affective deficits experienced by patients with cerebellar abnormalities, as SCA patients. Nevertheless, conclusions remain tentative at this stage due to the heterogeneity characterizing stimulation protocols, study methodologies and patients' samples.

Functional connectivity between the cerebellar vermis and cerebrum distinguishes early treatment response for major depressive episodes in adolescents

BACKGROUND

The absence of biomarkers for predicting treatment response in adolescent mood disorder calls for further research. The vermis, a component of the cerebellum, is involved in mood disorder pathophysiology and relates to clinical symptoms and treatment outcomes. We investigated vermis functional connectivity (FC) as an early marker for treatment response identification.

METHOD

One hundred thirty-two adolescents with mood disorders including major depressive disorder or bipolar disorder, were recruited, who were experiencing a major depressive episode. All adolescents underwent baseline and 2-week treatment resting-state MRI scans. Hamilton Rating Scale for Depression (HAMD) assessments were completed to assess the severity of symptoms. Patients were divided into treatment-responsive (≥50 % HAMD reduction, n = 75) and treatment-unresponsive subgroups (n = 57). Vermis FCs were compared between subgroups at baseline. And we compared the pre- and post-treatment FC differences within subgroups.

RESULT

Higher vermis-left temporal lobe FC in treatment-responsive group compared to treatment-unresponsive group at baseline. The FC value showed positive prognosis for the efficacy, with the area under the curve (AUC) of 0.760 (95 % confidence interval: 0.678-0.843, p < 0.001), suggesting higher vermis-temporal FC is benefit to improve treatment-response. Furthermore, post-treatment analysis showed significant increases in the vermis-right frontal lobe FC values between in all patients, suggesting that vermis-frontal FCs were independent of treatment-outcome.

LIMITATION

Sample size was relatively small, which may limit the generalizability of our results.

CONCLUSION

Our study revealed that the FC between the vermis and the cortex is not only associated with symptom alleviation but also predictive of treatment outcomes.

The Cerebellum Gets Social: Evidence from an Exploratory Study of Cerebellar, Neurodevelopmental, and Psychiatric Disorders

Social prediction is a key feature of social cognition (SC), a function in which the modulating role of the cerebellum is recognized. Accordingly, cerebellar alterations are reported in cerebellar pathologies, neurodevelopmental disorders, and psychiatric conditions that show SC deficits. Nevertheless, to date, no study has directly compared populations representative of these three conditions with respect to SC and cerebellar alterations. Therefore, the present exploratory study aimed to compare the SC profiles of individuals with cerebellar neurodegenerative disorders (CB), autism (ASD), bipolar disorder type 2 (BD2), or healthy subjects (HS) using a battery of social tests requiring different degrees of prediction processing. The patterns of cerebellar gray matter (GM) alterations were compared among the groups using voxel-based morphometry. Compared to HS, the clinical groups showed common SC deficits in tasks involving a moderate to high level of prediction. The behavioral results of the clinical groups are consistent with the presence of overlapping GM reduction in cerebellar right Crus II, an area notably involved in complex social processing and prediction. Although exploratory and preliminary, these results deepen the cerebellar role in social prediction and highlight the transdiagnostic value of the cerebellum in social functioning and prediction in pathologies of different aetiologies, forecasting novel possibilities for shared interventions.

The role of the cerebellum in sequencing and predicting social and non-social events in patients with bipolar disorder

Introduction

Advances in the operational mode of the cerebellum indicate a role in sequencing and predicting non-social and social events, crucial for individuals to optimize high-order functions, such as Theory of Mind (ToM). ToM deficits have been described in patients with remitted bipolar disorders (BD). The literature on BD patients' pathophysiology reports cerebellar alterations; however, sequential abilities have never been investigated and no study has previously focused on prediction abilities, which are needed to properly interpret events and to adapt to changes.

Methods

To address this gap, we compared the performance of BD patients in the euthymic phase with healthy controls using two tests that require predictive processing: a ToM test that require implicit sequential processing and a test that explicitly assesses sequential abilities in non-ToM functions. Additionally, patterns of cerebellar gray matter (GM) alterations were compared between BD patients and controls using voxel-based morphometry.

Results

Impaired ToM and sequential skills were detected in BD patients, specifically when tasks required a greater predictive load. Behavioral performances might be consistent with patterns of GM reduction in cerebellar lobules Crus I-II, which are involved in advanced human functions.

Discussion

These results highlight the importance of deepening the cerebellar role in sequential and prediction abilities in patients with BD.

The cerebellum gains weight: A systematic review of alterations in cerebellar volume and cerebro-cerebellar functional alterations in individuals with eating disorders

BACKGROUND

Brain imaging studies on eating disorders (EDs) often reported volumetric and functional changes involving the cerebellum. Nevertheless, few studies performed in-depth examinations and suggested a cerebellar role in the EDs' pathophysiology.

METHODS

A systematic literature search on volumetric changes and functional alterations involving the cerebellum in individuals with EDs was conducted using PubMed, PsychInfo and Web of Science. This review was conducted according to the Preferred Reporting Items for Systematic Reviews (PRISMA) statement and Rayyan web application for screening studies.

RESULTS

Twenty-four papers reporting cerebellar alterations in individuals with EDs were included in the study: 9 assessing brain volumetric changes, 9 investigating task-based functional brain activation and 6 investigating brain functional connectivity at rest. Most studies focused on anorectic-type EDs (n.22), while fewer involved bulimic-type EDs (n.9) and eating disorders not otherwise specified (n.2), revealing subtypes-specific patterns of altered cerebellar volume and functionality.

CONCLUSIONS

This review proposes critical arguments to consider the cerebellum as a key structure in the pathophysiology of EDs that requires further forthcoming exploration.

Theory of mind profile and cerebellar alterations in remitted bipolar disorder 1 and 2: a comparison study

The literature on social cognition abilities in bipolar disorder (BD) is controversial about the occurrence of theory of mind (ToM) alterations. In addition to other cerebral structures, such as the frontal and limbic areas, the processing of socially relevant stimuli has also been attributed to the cerebellum, which has been demonstrated to be involved in the above-mentioned disorder. Nevertheless, the cerebellar contribution to ToM deficits in bipolar patients needs to be elucidated further. To this aim, two tests assessing different components of ToM were used to evaluate the ability to appreciate affective and mental states of others in 17 individuals with a diagnosis of BD type 1 (BD1) and 13 with BD type 2 (BD2), both in the euthymic phase, compared to healthy matched controls. Cerebellar gray matter (GM) volumes were extracted and compared between BD1 and controls and BD2 and controls by using voxel-based morphometry. The results showed that BD1 patients were compromised in the cognitive and advanced components of ToM, while the BD2 ToM profile resulted in a more widespread compromise, also involving affective and automatic components. Both overlapping and differing areas of cerebellar GM reduction were found. The two groups of patients presented a pattern of GM reduction in cerebellar portions that are known to be involved in the affective and social domains, such as the vermis and Crus I and Crus II. Interestingly, in both BD1 and BD2, positive correlations were detected between lower ToM scores and decreased volumes in the cerebellum. Overall, BD2 patients showed a more compromised ToM profile and greater cerebellar impairment than BD1 patients. The different patterns of structural abnormalities may account for the different ToM performances evidenced, thus leading to divergent profiles between BD1 and BD2.

A missing link in affect regulation: the cerebellum

The cerebellum is one-third the size of the cerebrum yet holds twice the number of neurons. Historically, its sole function was thought to be in the calibration of smooth movements through the creation and ongoing modification of motor programs. This traditional viewpoint has been challenged by findings showing that cerebellar damage can lead to striking changes in non-motor behavior, including emotional changes. In this manuscript, we review the literature on clinical and subclinical affective disturbances observed in individuals with lesions to the cerebellum. Disorders include pathological laughing and crying, bipolar disorder, depression and mixed mood changes. We propose a theoretical model based on cerebellar connectivity to explain how the cerebellum calibrates affect. We conclude with actionable steps for future researchers to test this model and improve upon the limitations of past literature.

Altered cerebellar gray matter and cerebellar-cortex resting-state functional connectivity in patients with bipolar disorder Ⅰ

BACKGROUND

Bipolar disorder (BP) is a common psychiatric disorder characterized by extreme fluctuations in mood. Recent studies have indicated the involvement of cerebellum in the pathogenesis of BP. However, no study has focused on the precise role of cerebellum exclusively in patients with bipolar I disorder (BP-I).

METHODS

Forty-five patients with BP-I and 40 healthy controls were recruited. All subjects underwent clinical evaluation and Magnetic Resonance diffusion Tension Imaging scans. For structural images, we used a spatially unbiased infratentorial template toolbox to isolate the cerebellum and then preformed voxel-based morphometry (VBM) analyses to assess the difference in cerebellar gray matter volume (GMV) between the two groups. For the functional images, we chose the clusters that survived from VBM analysis as seeds and performed functional connectivity (FC) analysis. Between-group differences were assessed using the independent Students t test or the nonparametric Mann-Whitney U Test. For multiple comparisons, the results were further corrected with Gaussian random field (GRF) approach (voxel-level P < 0.001, cluster-level P < 0.05).

RESULTS

Compared with healthy controls, BP-I patients showed significantly decreased GMV in left lobule V and left lobule VI (P < 0.05, GRF corrected). The FC of cerebellum with bilateral superior temporal gyrus, bilateral insula, bilateral rolandic operculum, right putamen, and left precentral gyrus was disrupted in BP-I patients (P < 0.05, GRF corrected).

CONCLUSIONS

BP-I patients showed decreased cerebellar GMV and disrupted cerebellar-cortex resting-state FC. This suggests that cerebellar abnormalities may play an important role in the pathogenesis of BP-I.

The Role of the Posterior Cerebellum in Dysfunctional Social Sequencing

Recent advances in social neuroscience have highlighted the critical role of the cerebellum in social cognition, and especially the posterior cerebellum. Studies have supported the view that the posterior cerebellum builds internal action models of our social interactions to predict how other people's actions will be executed and what our most likely responses are to these actions. This mechanism allows to better anticipate action sequences during social interactions in an automatic and intuitive way and to fine-tune these anticipations, making it easier to understand other's social behaviors and mental states (e.g., beliefs, intentions, traits). In this paper, we argue that the central role of the posterior cerebellum in identifying and automatizing social action sequencing provides a fruitful starting point for investigating social dysfunctions in a variety of clinical pathologies, such as autism, obsessive-compulsive and bipolar disorder, depression, and addiction. Our key hypothesis is that dysfunctions of the posterior cerebellum lead to under- or overuse of inflexible social routines and lack of plasticity for learning new, more adaptive, social automatisms. We briefly review past research supporting this view and propose a program of research to test our hypothesis. This approach might alleviate a variety of mental problems of individuals who suffer from inflexible automatizations that stand in the way of adjustable and intuitive social behavior, by increasing posterior cerebellar plasticity using noninvasive neurostimulation or neuro-guided training programs.

Aberrant Cerebello-Cerebral Connectivity in Remitted Bipolar Patients 1 and 2: New Insight into Understanding the Cerebellar Role in Mania and Hypomania

Bipolar disorder (BD) is a major mental illness characterized by periods of (hypo) mania and depression with inter-episode remission periods. Functional studies in BD have consistently implicated a set of linked cortical and subcortical limbic regions in the pathophysiology of the disorder, also including the cerebellum. However, the cerebellar role in the neurobiology of BD still needs to be clarified. Seventeen euthymic patients with BD type1 (BD1) (mean age/SD, 38.64/13.48; M/F, 9/8) and 13 euthymic patients with BD type 2 (BD2) (mean age/SD, 41.42/14.38; M/F, 6/7) were compared with 37 sex- and age-matched healthy subjects (HS) (mean age/SD, 45.65/14.15; M/F, 15/22). T1 weighted and resting-state functional connectivity (FC) scans were acquired. The left and right dentate nucleus were used as seed regions for the seed based analysis. FC between each seed and the rest of the brain was compared between patients and HS. Correlations between altered cerebello-cerebral connectivity and clinical scores were then investigated. Different patterns of altered dentate-cerebral connectivity were found in BD1 and BD2. Overall, impaired dentate-cerebral connectivity involved regions of the anterior limbic network specifically related to the (hypo)manic states of BD. Cerebello-cerebral connectivity is altered in BD1 and BD2. Interestingly, the fact that these altered FC patterns persist during euthymia, supports the hypothesis that cerebello-cerebral FC changes reflect the neural correlate of subthreshold symptoms, as trait-based pathophysiology and/or compensatory mechanism to maintain a state of euthymia.