The cerebellum: so much more

Role of cerebellum in deglutition and deglutition disorders

The objective of this review is to gather available evidence regarding the role of the cerebellum in swallowing-related functions. We reviewed literature on cerebellar functions related to healthy swallowing, patterns of dysphagia in individuals with cerebellar lesions, and the role of the cerebellum in therapeutic intervention of neurogenic dysphagia since 1980. A collective understanding of these studies suggests that both hemispheres of the cerebellum, predominantly the left, participate in healthy swallowing. Also, it appears that the cerebellum contributes to specific physiological functions within the entire act of swallowing, but this is not clearly understood. The understanding of patterns of dysphagia in cerebellar lesions remains ambiguous with equivocal results across a small number of studies. The cerebellum appears to be involved in oral exercises for dysphagia in the relationship between oral movements in such exercises, and deglutition remains uncertain. There is increasing evidence to suggest successful use of transcranial magnetic stimulation of the cerebellum to improve neuromotor control of swallowing. Future studies should address activation of the cerebellum with swallowing of different consistencies and tastes in healthy adults to gain better insights. Studies should also investigate dynamics of neural activation during different stages of recovery from dysphagia following strokes to cortical centers to determine if the cerebellum plays a compensatory role during instances of increased neural demands.

Cerebellar abnormalities in Huntington's disease: a role in motor and psychiatric impairment?

The cerebellum has received limited attention in Huntington's disease (HD), despite signs of possible cerebellar dysfunction, including motor incoordination and impaired gait, which are currently attributed to basal ganglia atrophy and disrupted fronto-striatal circuits. This study is the first to investigate a potential contribution of macro- and microstructural cerebellar damage to clinical manifestations of HD. T1- and diffusion-weighted 3T magnetic resonance imaging (MRI) scans were obtained from 12 controls and 22 early-stage HD participants. Manual delineation and voxel-based morphometry were used to assess between-group differences in cerebellar volume, and diffusion metrics were compared between groups within the cerebellar gray and white matter. Associations between these imaging measures and clinical scores were examined within the HD group. Reduced paravermal volume was detected in HD compared with controls using voxel-based morphometry (P < 0.05), but no significant volumetric differences were found using manual delineation. Diffusion abnormalities were detected in both cerebellar gray matter and white matter. Smaller cerebellar volumes, although not significantly reduced, were significantly associated with impaired gait and psychiatric morbidity and of borderline significance with pronate/supinate-hand task performance. Abnormal cerebellar diffusion was associated with increased total motor score, impaired saccade initiation, tandem walking, and timed finger tapping. In conclusion, atrophy of the paravermis, possibly encompassing the cerebellar nuclei, and microstructural abnormalities within the cerebellum may contribute to HD neuropathology. Aberrant cerebellar diffusion and reduced cerebellar volume together associate with impaired motor function and increased psychiatric symptoms in stage I HD, potentially implicating the cerebellum more centrally in HD presentation than previously recognized.

Cerebellum engages in automation of verb-generation skill

Numerous studies have shown cerebellar involvement in item-specific association, a form of explicit learning. However, very few have demonstrated cerebellar participation in automation of non-motor cognitive tasks. Applying fMRI to a repeated verb-generation task, we sought to distinguish cerebellar involvement in learning of item-specific noun-verb association and automation of verb generation skill. The same set of nouns was repeated in six verb-generation blocks so that subjects practiced generating verbs for the nouns. The practice was followed by a novel block with a different set of nouns. The cerebellar vermis (IV/V) and the right cerebellar lobule VI showed decreased activation following practice; activation in the right cerebellar Crus I was significantly lower in the novel challenge than in the initial verb-generation task. Furthermore, activation in this region during well-practiced blocks strongly correlated with improvement of behavioral performance in both the well-practiced and the novel blocks, suggesting its role in the learning of general mental skills not specific to the practiced noun-verb pairs. Therefore, the cerebellum processes both explicit verbal associative learning and automation of cognitive tasks. Different cerebellar regions predominate in this processing: lobule VI during the acquisition of item-specific association, and Crus I during automation of verb-generation skills through practice.

Pervasive rightward asymmetry shifts of functional networks in autism spectrum disorder

IMPORTANCE

Autism spectrum disorder (ASD) is a brain-based pervasive developmental disorder, which-by growing consensus-is associated with abnormal organization of functional networks. Several previous studies of ASD have indicated atypical hemispheric asymmetries for language.

OBJECTIVE

To examine the asymmetry of functional networks using a data-driven approach for a comprehensive investigation of hemispheric asymmetry in ASD.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study involved 24 children with ASD and 26 matched typically developing children at San Diego State University and the University of California, San Diego. Data from 10 children had to be excluded for excessive motion, resulting in final samples of 20 participants per group.

MAIN OUTCOMES AND MEASURES

Asymmetry indices of functional networks identified from independent component analysis of resting-state functional magnetic resonance imaging data.

RESULTS

Temporal concatenation independent component analysis, performed separately in each group, showed significant group differences in asymmetry indices for 10 out of 17 functional networks. Without exception, these networks (visual, auditory, motor, executive, language, and attentional) showed atypical rightward asymmetry shifts in the ASD group.

CONCLUSIONS AND RELEVANCE

Atypical rightward asymmetry may be a pervasive feature of functional brain organization in ASD, affecting sensorimotor, as well as higher cognitive, domains.

Neural circuits of the cerebellum: hypothesis for function

The rapid growth of cerebellar research is going to clarify several aspects of cellular and circuit physiology. However, the concepts about cerebellar mechanisms of function are still largely related to clinical observations and to models elaborated before the last discoveries appeared. In this paper, the major issues are revisited, suggesting that previous concepts can now be refined and modified. The cerebellum is fundamentally involved in timing and in controlling the ordered and precise execution of motor sequences. The fast reaction of the cerebellum to the inputs is sustained by specific cellular mechanisms ensuring precision on the millisecond scale. These include burst-burst reconversion in the granular layer and instantaneous frequency modulation on the 100-Hz band in Purkinje and deep cerebellar nuclei cells. Precisely timed signals can be used for perceptron operations in Purkinje cells and to establish appropriate correlations with climbing fiber signals inducing learning at parallel fiber synapses. In the granular layer, plasticity turns out to be instrumental to timing, providing a conceptual solution to the discrepancy between cerebellar learning and timing. The granular layer sub-circuit can be tuned by long-term synaptic plasticity and synaptic inhibition to delay the incoming signals over a 100-ms range. For longer sequences, large circuit sections can be entrained into coherent activity in 100-ms cycles. These dynamic aspects, which have not been accounted for by original theories, could in fact represent the essence of cerebellar functioning. It is suggested that the cerebellum can, in this way, operate the realignment of temporally incongruent signals, allowing their binding and pattern recognition in Purkinje cells. The demonstration of these principles, their behavioral relevance and their relationship with internal model theories represent a challenge for future cerebellar research.

Altered cerebellar feedback projections in Asperger syndrome

It has been proposed that the biological basis of autism spectrum disorder includes cerebellar 'disconnection'. However, direct in vivo evidence in support of this is lacking. Here, the microstructural integrity of cerebellar white matter in adults with Asperger syndrome was studied using diffusion tensor magnetic resonance tractography. Fifteen adults with Asperger syndrome and 16 age-IQ-gender-matched healthy controls underwent diffusion tensor magnetic resonance imaging. For each subject, tract-specific measurements of mean diffusivity and fractional anisotropy were made within the inferior, middle, superior cerebellar peduncles and short intracerebellar fibres. No group differences were observed in mean diffusivity. However, people with Asperger syndrome had significantly lower fractional anisotropy in the short intracerebellar fibres (p<0.001) and right superior cerebellar (output) peduncle (p<0.001) compared to controls; but no difference in the input tracts. Severity of social impairment, as measured by the Autistic Diagnostic Interview, was negatively correlated with diffusion anisotropy in the fibres of the left superior cerebellar peduncle. These findings suggest a vulnerability of specific cerebellar neural pathways in people with Asperger syndrome. The localised abnormalities in the main cerebellar outflow pathway may prevent the cerebral cortex from receiving those cerebellar feedback inputs necessary for a successful adaptive social behaviour.

Visualization of the deep cerebellar nuclei using quantitative T1 and rho magnetic resonance imaging at 3 Tesla

The cerebellum coordinates movement, thought and emotion through its feedback projections from the deep cerebellar nuclei. Despite recent advancement in our understanding of the functions of the cerebellar cortex, little is known about the functional correlates of the deep cerebellar nuclei in humans. This is mainly due to the inability of current MRI techniques to visualize the cerebellar nuclei and therefore perform in vivo clinico-anatomical correlation studies in patient populations. Here we visualize in vivo the detailed anatomy of the dentate nucleus and other cerebellar nuclei using quantitative T1 and proton density (rho) imaging. Compared to conventional qualitative T1, T2 or T2*-weighted imaging, quantitative T1 and proton density (rho) imaging facilitates direct visualization of the dentate and interposed nuclei, allowing us to perform segmentation and volumetric measurements of the dentate nucleus. Also the fine architecture of the microgyric and macrogyric dentate nucleus was visible on the high-resolution images. The high concentration of paramagnetic iron within the cerebellar nuclei and the resulting local field inhomogeneities surrounding the iron-containing nuclei is believed to be responsible for the observed effect on T1 and proton density signal. The application of this technique to disorders with cerebellar dysfunction could provide new insight into pathologies like autism and movement disorders.

Participação do cerebelo no processamento auditivo

O cerebelo era tradicionalmente visto como um órgão coordenador da motricidade, entretanto é atualmente considerado como um importante centro de integração de sensibilidades e coordenação de várias fases do processo cognitivo. OBJETIVO: é sistematizar as informações da literatura quanto à participação do cerebelo na percepção auditiva. MÉTODOS: foram selecionados na literatura trabalhos em animais sobre a fisiologia e anatomia das vias auditivas do cerebelo, além de trabalhos em humanos sobre diversas funções do cerebelo na percepção auditiva. Foram discutidos os achados da literatura, que há evidências que o cerebelo participa das seguintes funções cognitivas relacionadas à audição: geração verbal; processamento auditivo; atenção auditiva; memória auditiva; raciocínio abstrato; timing; solução de problemas; discriminação sensorial; informação sensorial; processamento da linguagem; operações lingüísticas. CONCLUSÃO: Foi constatado que são incompletas as informações sobre as estruturas, funções e vias auditivas do cerebelo.

Cerebellar activity switches hemispheres with cerebral recovery in aphasia

The right postero-lateral cerebellum participates with the left frontal lobe in the selection and production of words. Using fMRI, we examined whether cerebellar activity switches hemispheres in parallel with recruitment of putative compensatory right homologous frontal regions in post-stroke aphasia. Re-examining the data of Blasi et al. [Blasi, V., Young, A. C., Tansy, A. P., Petersen, S. E., Snyder, A. Z., & Corbetta, M. (2002). Word retrieval learning modulates right frontal cortex in patients with left frontal damage. Neuron, 36(1), 159-170], we asked: (1) if activity in the right cerebellum was disrupted by a left frontal lesion, (2) if activity switched to the left cerebellum, and (3) if activity in the left cerebellum was modulated by learning, as was right frontal cortex. Fourteen age-matched controls and eight mildly aphasic stroke patients participated. Aphasic participants all had lesions due to unilateral left hemisphere stroke at or near Broca's area. Subjects silently performed a word stem completion task with either novel or repeated items. Activity in right cerebellum of aphasic individuals was minimal and was not modulated by learning, as for controls. However, we observed robust learning-related attenuation of the BOLD signal in the left postero-lateral cerebellum consistent with learning-related effects in right frontal cortex. These findings support the hypothesis that right frontal and left cerebellar circuits are likely to be functionally relevant to recovered/residual verbal function.

The localisation of urocortin in the adult rat cerebellum: a light and electron microscopic study

Light and electron microscopic immunocytochemistry was used to identify the cellular and subcellular localisation of urocortin in the adult rat cerebellum. Urocortin immunoreactivity (UCN-ir) was visualised throughout the cerebellum, yet predominated in the posterior vermal lobules, especially lobules IX and X, the flocculus, paraflocculus and deep cerebellar nuclei. Cortical immunoreactivity was most evident in the Purkinje cell layer and molecular layer. Reaction product, though sparse, was found in the somata of Purkinje cells, primarily in the region of the Golgi apparatus. Purkinje cell dendritic UCN-ir was compartmentalised, with it being prevalent in proximal regions especially where climbing fibres synapsed, yet absent in distal regions where parallel fibres synapsed. In the Purkinje cell layer, the labelling was also contained in axonal terminals, synapsing directly on Purkinje cell somata. These were identified as axon terminals of basket cells based on their morphology. Terminals of stellate cells in the upper molecular layer also expressed the peptide. Whilst somata of inferior olivary neurones showed intense immunoreactivity, axonal labelling was indistinct, with only the terminals of climbing fibres containing reaction product. UCN-ir in the mossy fibre-parallel fibre system was restricted to mossy fibre rosettes of mainly posterior lobules and the varicose terminals of parallel fibres. Furthermore, labelling also was prevalent in glial perikarya and their sheaths. The current study shows, firstly, that urocortin enjoys a close ligand-receptor symmetry in the cerebellum, probably to a greater degree than corticotropin-releasing factor since corticotropin-releasing factor itself is found exclusively in the two major cerebellar afferent systems. Its congregation in excitatory and inhibitory axonal terminals suggests a significant degree of participation in the synaptic milieu, perhaps in the capacity as a neurotransmitter or effecting the release of co-localised neurotransmitters. Finally, its unique distribution in the Purkinje cell dendrite might serve as an anatomical marker of discrete populations of dendritic spines.

Decreased benzodiazepine receptor density in the cerebellum of early blind human subjects

As a first approach to study the effect of early visual deprivation in the GABA-ergic inhibitory system, the distribution of benzodiazepine receptors (BZR) was accurately estimated using [11C]flumazenil ([11C]FMZ). Measurements were carried out in five subjects who became blind early in life and in five sighted control subjects. The interactions between [11C]FMZ and BZR were described using a non-linear compartmental analysis which permitted to estimate the BZR synaptic density independently of other model parameters. The distribution of BZR in the visual areas and other cortical regions of blind subjects was qualitatively and quantitatively similar to that of controls. However, the BZR density in the cerebellum was significantly lower in blind than in control subjects (P<0.01). Our findings suggest that modifications of the cerebellar neural circuitry may be concomitant to the already observed compensatory reorganization in cerebral areas of blind subjects.