Regional functionality of the cerebellum

Heterogeneity in Slow Synaptic Transmission Diversifies Purkinje Cell Timing

The cerebellum plays an important role in diverse brain functions, ranging from motor learning to cognition. Recent studies have suggested that molecular and cellular heterogeneity within cerebellar lobules contributes to functional differences across the cerebellum. However, the specific relationship between molecular and cellular heterogeneity and diverse functional outputs of different regions of the cerebellum remains unclear. Here, we describe a previously unappreciated form of synaptic heterogeneity at parallel fiber synapses to Purkinje cells in the mouse cerebellum (both sexes). In contrast to uniform fast synaptic transmission, we found that the properties of slow synaptic transmission varied by up to threefold across different lobules of the mouse cerebellum, resulting in surprising heterogeneity. Depending on the location of a Purkinje cell, the time of peak of slow synaptic currents varied by hundreds of milliseconds. The duration and decay time of these currents also spanned hundreds of milliseconds, based on lobule. We found that, as a consequence of the heterogeneous synaptic dynamics, the same brief input stimulus was transformed into prolonged firing patterns over a range of timescales that depended on Purkinje cell location.

Cerebellar transcranial magnetic stimulation for improving balance capacity and activity of daily living in stroke patients: a systematic review and meta-analysis

BACKGROUND

The application of cerebellar transcranial magnetic stimulation (TMS) in stroke patients has received increasing attention due to its neuromodulation mechanisms. However, studies on the effect and safety of cerebellar TMS to improve balance capacity and activity of daily living (ADL) for stroke patients are limited. This systematic review and meta-analysis aimed to investigate the effect and safety of cerebellar TMS on balance capacity and ADL in stroke patients.

METHOD

A systematic search of seven electronic databases (PubMed, Embase, Web of Science, Cochrane Central Register of Controlled Trials, China National Knowledge Infrastructure, Wanfang and Chinese Scientific Journal) were conducted from their inception to October 20, 2023. The randomized controlled trials (RCTs) of cerebellar TMS on balance capacity and/or ADL in stroke patients were enrolled. The quality of included studies were assessed by Physiotherapy Evidence Database (PEDro) scale.

RESULTS

A total of 13 studies involving 542 participants were eligible. The pooled results from 8 studies with 357 participants showed that cerebellar TMS could significantly improve the post-intervention Berg balance scale (BBS) score (MD = 4.24, 95%CI = 2.19 to 6.29, P < 0.00001; heterogeneity, I2 = 74%, P = 0.0003). The pooled results from 4 studies with 173 participants showed that cerebellar TMS could significantly improve the post-intervention Time Up and Go (TUG) (MD=-1.51, 95%CI=-2.8 to -0.22, P = 0.02; heterogeneity, I2 = 0%, P = 0.41). The pooled results from 6 studies with 280 participants showed that cerebellar TMS could significantly improve the post-intervention ADL (MD = 7.75, 95%CI = 4.33 to 11.17, P < 0.00001; heterogeneity, I2 = 56%, P = 0.04). The subgroup analysis showed that cerebellar TMS could improve BBS post-intervention and ADL post-intervention for both subacute and chronic stage stroke patients. Cerebellar high frequency TMS could improve BBS post-intervention and ADL post-intervention. Cerebellar TMS could still improve BBS post-intervention and ADL post-intervention despite of different cerebellar TMS sessions (less and more than 10 TMS sessions), different total cerebellar TMS pulse per week (less and more than 4500 pulse/week), and different cerebellar TMS modes (repetitive TMS and Theta Burst Stimulation). None of the studies reported severe adverse events except mild side effects in three studies.

CONCLUSIONS

Cerebellar TMS is an effective and safe technique for improving balance capacity and ADL in stroke patients. Further larger-sample, higher-quality, and longer follow-up RCTs are needed to explore the more reliable evidence of cerebellar TMS in the balance capacity and ADL, and clarify potential mechanisms.

Compressed cerebellar functional connectome hierarchy in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is an inherited movement disorder characterized by a progressive decline in motor coordination. Despite the extensive functional connectivity (FC) alterations reported in previous SCA3 studies in the cerebellum and cerebellar-cerebral pathways, the influence of these FC disturbances on the hierarchical organization of cerebellar functional regions remains unclear. Here, we compared 35 SCA3 patients with 48 age- and sex-matched healthy controls using a combination of voxel-based morphometry and resting-state functional magnetic resonance imaging to investigate whether cerebellar hierarchical organization is altered in SCA3. Utilizing connectome gradients, we identified the gradient axis of cerebellar hierarchical organization, spanning sensorimotor to transmodal (task-unfocused) regions. Compared to healthy controls, SCA3 patients showed a compressed hierarchical organization in the cerebellum at both voxel-level (p < .05, TFCE corrected) and network-level (p < .05, FDR corrected). This pattern was observed in both intra-cerebellar and cerebellar-cerebral gradients. We observed that decreased intra-cerebellar gradient scores in bilateral Crus I/II both negatively correlated with SARA scores (left/right Crus I/II: r = -.48/-.50, p = .04/.04, FDR corrected), while increased cerebellar-cerebral gradients scores in the vermis showed a positive correlation with disease duration (r = .48, p = .04, FDR corrected). Control analyses of cerebellar gray matter atrophy revealed that gradient alterations were associated with cerebellar volume loss. Further FC analysis showed increased functional connectivity in both unimodal and transmodal areas, potentially supporting the disrupted cerebellar functional hierarchy uncovered by the gradients. Our findings provide novel evidence regarding alterations in the cerebellar functional hierarchy in SCA3.

Dysphagia following cerebellar stroke: analyzing the contribution of the cerebellum to swallowing function

Swallowing is essential for human health, and the cerebellum is crucial for motor movement regulation. Cerebellar strokes may cause dysphagia, but their exact effects remain unexplored in swallowing function. Therefore, the aim of this study was to analyze the precise clinical characteristics of the oral and pharyngeal phases of swallowing after cerebellar stroke and to critically discuss the cerebellum's contribution to swallowing. The study involved 34 participants with cerebellar strokes, gathered through convenience sampling. Neurologists diagnosed isolated strokes, and a speech and language pathologist examined swallowing ability using the Mann Assessment of Swallowing Ability. The study found that 52.9% of people experienced dysphagia after a cerebellar stroke. Dysphagia was significantly associated with a higher risk of aspiration. Age was also significantly correlated with dysphagia. No significant correlation was found between swallowing ability and sex. In conclusion, this study suggests isolated cerebellar stroke can adversely affect the motor and non-motor aspects of swallowing and cause severe dysphagia and aspiration risk. Thus, early diagnosis and timely management of dysphagia following a cerebellar stroke can help prevent serious consequences.

Increased functional connectivity coupling with supplementary motor area in blepharospasm at rest

OBJECTIVE

To explore the abnormalities of brain function in blepharospasm (BSP) and to illustrate its neural mechanisms by assuming supplementary motor area (SMA) as the entry point.

METHODS

Twenty-five patients with BSP and 23 controls underwent resting-state functional MRI, seed-based functional connectivity (FC), correlation analysis, receiver operating characteristic curve (ROC) analysis, and support vector machine (SVM) were applied to process the data.

RESULTS

Patients showed that the left medial prefrontal cortex (MPFC), left lingual gyrus, right cerebellar crus I, and right lingual gyrus/cerebellar crus I had enhanced FC with the left SMA, whereas the right inferior temporal gyrus (ITG) had enhanced FC with the right SMA relative to controls. The FC between the left MPFC and left SMA was positively correlated with symptomatic severity. The ROC analysis verified that the abnormal FCs demonstrated in this study can separate patients and controls at high sensitivity and specificity. SVM analysis exhibited that combined FCs of the left SMA were optimal for distinguishing patients and control group at the accuracy of 89.58%, with sensitivity of 92.00% and specificity of 86.96%.

CONCLUSIONS

Several brain networks partake in the neurobiology of BSP. SMA plays a vital role in several brain networks and might be the key pathogenic factor in BSP.

SIGNIFICANCE

Providing novel evidence for the engagement of the MPFC in the motor symptoms of BSP, enhancing credibility of the thesis that SMA regulates the neurobiology of BSP, and providing ideas of screening susceptible population of BSP using neuroimaging.

Development, circuitry, and function of the zebrafish cerebellum

The cerebellum represents a brain compartment that first appeared in gnathostomes (jawed vertebrates). Besides the addition of cell numbers, its development, cytoarchitecture, circuitry, physiology, and function have been highly conserved throughout avian and mammalian species. While cerebellar research in avian and mammals is extensive, systematic investigations on this brain compartment in zebrafish as a teleostian model organism started only about two decades ago, but has provided considerable insight into cerebellar development, physiology, and function since then. Zebrafish are genetically tractable with nearly transparent small-sized embryos, in which cerebellar development occurs within a few days. Therefore, genetic investigations accompanied with non-invasive high-resolution in vivo time-lapse imaging represents a powerful combination for interrogating the behavior and function of cerebellar cells in their complex native environment.

Mega-Enhancer Bodies Organize Neuronal Long Genes in the Cerebellum

Dynamic regulation of gene expression plays a key role in establishing the diverse neuronal cell types in the brain. Recent findings in genome biology suggest that three-dimensional (3D) genome organization has important, but mechanistically poorly understood functions in gene transcription. Beyond local genomic interactions between promoters and enhancers, we find that cerebellar granule neurons undergoing differentiation in vivo exhibit striking increases in long-distance genomic interactions between transcriptionally active genomic loci, which are separated by tens of megabases within a chromosome or located on different chromosomes. Among these interactions, we identify a nuclear subcompartment enriched for near-megabase long enhancers and their associated neuronal long genes encoding synaptic or signaling proteins. Neuronal long genes are differentially recruited to this enhancer-dense subcompartment to help shape the transcriptional identities of granule neuron subtypes in the cerebellum. SPRITE analyses of higher-order genomic interactions, together with IGM-based 3D genome modeling and imaging approaches, reveal that the enhancer-dense subcompartment forms prominent nuclear structures, which we term mega-enhancer bodies. These novel nuclear bodies reside in the nuclear periphery, away from other transcriptionally active structures, including nuclear speckles located in the nuclear interior. Together, our findings define additional layers of higher-order 3D genome organization closely linked to neuronal maturation and identity in the brain.

Purkinje cell microzones mediate distinct kinematics of a single movement

The classification of neuronal subpopulations has significantly advanced, yet its relevance for behavior remains unclear. The highly organized flocculus of the cerebellum, known to fine-tune multi-axial eye movements, is an ideal substrate for the study of potential functions of neuronal subpopulations. Here, we demonstrate that its recently identified subpopulations of 9+ and 9- Purkinje cells exhibit an intermediate Aldolase C expression and electrophysiological profile, providing evidence for a graded continuum of intrinsic properties among PC subpopulations. By identifying and utilizing two Cre-lines that genetically target these floccular domains, we show with high spatial specificity that these subpopulations of Purkinje cells participate in separate micromodules with topographically organized connections. Finally, optogenetic excitation of the respective subpopulations results in movements around the same axis in space, yet with distinct kinematic profiles. These results indicate that Purkinje cell subpopulations integrate in discrete circuits and mediate particular parameters of single movements.

Variations on the theme: focus on cerebellum and emotional processing

The cerebellum operates exploiting a complex modular organization and a unified computational algorithm adapted to different behavioral contexts. Recent observations suggest that the cerebellum is involved not just in motor but also in emotional and cognitive processing. It is therefore critical to identify the specific regional connectivity and microcircuit properties of the emotional cerebellum. Recent studies are highlighting the differential regional localization of genes, molecules, and synaptic mechanisms and microcircuit wiring. However, the impact of these regional differences is not fully understood and will require experimental investigation and computational modeling. This review focuses on the cellular and circuit underpinnings of the cerebellar role in emotion. And since emotion involves an integration of cognitive, somatomotor, and autonomic activity, we elaborate on the tradeoff between segregation and distribution of these three main functions in the cerebellum.

Characterizing the information transmission of inverse stochastic resonance and noise-induced activity amplification in neuronal systems

Purkinje cells exhibit a reduction of the mean firing rate at intermediate-noise intensities, which is somewhat reminiscent of the response enhancement known as "stochastic resonance" (SR). Although the comparison with the stochastic resonance ends here, the current phenomenon has been given the name "inverse stochastic resonance" (ISR). Recent research has demonstrated that the ISR effect, like its close relative "nonstandard SR" [or, more correctly, noise-induced activity amplification (NIAA)], has been shown to stem from the weak-noise quenching of the initial distribution, in bistable regimes where the metastable state has a larger attraction basin than the global minimum. To understand the underlying mechanism of the ISR and NIAA phenomena, we study the probability distribution function of a one-dimensional system subjected to a bistable potential that has the property of symmetry, i.e., if we change the sign of one of its parameters, we can obtain both phenomena with the same properties in the depth of the wells and the width of their basins of attraction subjected to Gaussian white noise with variable intensity. Previous work has shown that one can theoretically determine the probability distribution function using the convex sum between the behavior at small and high noise intensities. To determine the probability distribution function more precisely, we resort to the "weighted ensemble Brownian dynamics simulation" model, which provides an accurate estimate of the probability distribution function for both low and high noise intensities and, most importantly, for the transition of both behaviors. In this way, on the one hand, we show that both phenomena emerge from a metastable system where, in the case of ISR, the global minimum of the system is in a state of lower activity, while in the case of NIAA, the global minimum is in a state of increased activity, the importance of which does not depend on the width of the basins of attraction. On the other hand, we see that quantifiers such as Fisher information, statistical complexity, and especially Shannon entropy fail to distinguish them, but they show the existence of the mentioned phenomena. Thus, noise management may well be a mechanism by which Purkinje cells find an efficient way to transmit information in the cerebral cortex.

Neural correlates of cocaine-induced conditioned place preference in the posterior cerebellar cortex

Introduction

Addictive drugs are potent neuropharmacological agents capable of inducing long-lasting changes in learning and memory neurocircuitry. With repeated use, contexts and cues associated with consumption can acquire motivational and reinforcing properties of abused drugs, triggering drug craving and relapse. Neuroplasticity underlying drug-induced memories takes place in prefrontal-limbic-striatal networks. Recent evidence suggests that the cerebellum is also involved in the circuitry responsible for drug-induced conditioning. In rodents, preference for cocaine-associated olfactory cues has been shown to correlate with increased activity at the apical part of the granular cell layer in the posterior vermis (lobules VIII and IX). It is important to determine if the cerebellum's role in drug conditioning is a general phenomenon or is limited to a particular sensory modality.

Methods

The present study evaluated the role of the posterior cerebellum (lobules VIII and IX), together with the medial prefrontal cortex (mPFC), ventral tegmental area (VTA), and nucleus accumbens (NAc) using a cocaine-induced conditioned place preference procedure with tactile cues. Cocaine CPP was tested using ascending (3, 6, 12, and 24 mg/kg) doses of cocaine in mice.

Results

Compared to control groups (Unpaired and Saline animals), Paired mice were able to show a preference for the cues associated with cocaine. Increased activation (cFos expression) of the posterior cerebellum was found in cocaine CPP groups and showed a positive correlation with CPP levels. Such increases in cFos activity in the posterior cerebellum significantly correlated with cFos expression in the mPFC.

Discussion

Our data suggest that the dorsal region of the cerebellum could be an important part of the network that mediates cocaine-conditioned behavior.

Proinflammatory activation of microglia in the cerebellum hyperexcites Purkinje cells to trigger ataxia

Specific medications to combat cerebellar ataxias, a group of debilitating movement disorders characterized by difficulty with walking, balance and coordination, are still lacking. Notably, cerebellar microglial activation appears to be a common feature in different types of ataxic patients and rodent models. However, direct evidence that cerebellar microglial activation in vivo is sufficient to induce ataxia is still lacking. Here, by employing chemogenetic approaches to manipulate cerebellar microglia selectively and directly, we found that specific chemogenetic activation of microglia in the cerebellar vermis directly leads to ataxia symptoms in wild-type mice and aggravated ataxic motor deficits in 3-acetylpyridine (3-AP) mice, a classic mouse model of cerebellar ataxia. Mechanistically, cerebellar microglial proinflammatory activation induced by either chemogenetic M3D(Gq) stimulation or 3-AP modeling hyperexcites Purkinje cells (PCs), which consequently triggers ataxia. Blockade of microglia-derived TNF-α, one of the most important proinflammatory cytokines, attenuates the hyperactivity of PCs driven by microglia. Moreover, chemogenetic inhibition of cerebellar microglial activation or suppression of cerebellar microglial activation by PLX3397 and minocycline reduces the production of proinflammatory cytokines, including TNF-α, to effectively restore the overactivation of PCs and alleviate motor deficits in 3-AP mice. These results suggest that cerebellar microglial activation may aggravate the neuroinflammatory response and subsequently induce dysfunction of PCs, which in turn triggers ataxic motor deficits. Our findings thus reveal a causal relationship between proinflammatory activation of cerebellar microglia and ataxic motor symptoms, which may offer novel evidence for therapeutic intervention for cerebellar ataxias by targeting microglia and microglia-derived inflammatory mediators.

Early Cerebellar Development in Relation to the Trigeminal System

Despite the wealth of knowledge of adult cerebellar connectivity, little is known about the developmental mechanisms that underpin its development. Early connectivity is important because it is the foundation of the neural networks crucial for neuronal function and serves as a scaffold on which later tracts form. Conventionally, it is believed that afferents from the vestibular system are the first to invade the cerebellum, at embryonic days (E) 11-E12/13 in mice, where they target the new born Purkinje cells. However, we have demonstrated that pioneer axons that originate from the trigeminal ganglia are already present in the cerebellar primordium by E9, a stage at which afferents from the vestibular ganglia have not yet reached the brainstem, where they target neurons of the cerebellar nuclei. An early-born subset of cerebellar nuclei may be derived from the mesencephalon. These may be the target of the earliest pioneer axons. They form the early connectivity at the rostral end. This is consistent with the notion that the formation of the antero-posterior axis follows a rostro-caudal sequence. The finding that trigeminal ganglion-derived pioneer axons enter the cerebellar primordium before Purkinje cells are born and target the cerebellar nuclei, reveals a novel perspective on the development of early cerebellar connectivity.

A rare additional lobe of cerebellum, projecting from its superior surface

Human cerebellum plays a vital role in motor coordination, regulation of muscle tone and maintaining the equilibrium of the body. It seldom shows anatomical/morphological variations. Herein, we report the presence of a small additional lobe projecting out on the superior surface of the right cerebellar hemisphere in the para-vermal area in an adult male cadaver. There was a notch on the tentorial surface of the occipital lobe of the right cerebral hemisphere, corresponding to the additional lobe of cerebellum. The additional lobe was histologically normal, with no evidence of any tumour cells. Knowledge of this variation is of importance to radiologists, neuroanatomists and neurosurgeons.

What Can We Learn from Synaptic Connectivity Maps about Cerebellar Internal Models?

The cerebellum is classically associated with fine motor control, motor learning, and timing of actions. However, while its anatomy is well described and many synaptic plasticity have been identified, the computation performed by the cerebellar cortex is still debated. We, here, review recent advances on how the description of the functional synaptic connectivity between granule cells and Purkinje cells support the hypothesis that the cerebellum stores internal models of the body coordinates. We propose that internal models are specific of the task and of the locomotor context of each individual.

Olivocerebellar control of movement symmetry

Coordination of bilateral movements is essential for a large variety of animal behaviors. The olivocerebellar system is critical for the control of movement, but its role in bilateral coordination has yet to be elucidated. Here, we examined whether Purkinje cells encode and influence synchronicity of left-right whisker movements. We found that complex spike activity is correlated with a prominent left-right symmetry of spontaneous whisker movements within parts, but not all, of Crus1 and Crus2. Optogenetic stimulation of climbing fibers in the areas with high and low correlations resulted in symmetric and asymmetric whisker movements, respectively. Moreover, when simple spike frequency prior to the complex spike was higher, the complex spike-related symmetric whisker protractions were larger. This finding alludes to a role for rebound activity in the cerebellar nuclei, which indeed turned out to be enhanced during symmetric protractions. Tracer injections suggest that regions associated with symmetric whisker movements are anatomically connected to the contralateral cerebellar hemisphere. Together, these data point toward the existence of modules on both sides of the cerebellar cortex that can differentially promote or reduce the symmetry of left and right movements in a context-dependent fashion.

Comparing Brain Functional Activities in Patients With Blepharospasm and Dry Eye Disease Measured With Resting-State fMRI

Background: Blepharospasm (BSP) and dry eye disease (DED) are clinically common diseases characterized by an increased blinking rate. A sustained eyelid muscle activity may alter the cortical sensorimotor concordance and lead to secondary functional changes. This study aimed to explore the central mechanism of BSP by assessing brain functional differences between the two groups and comparing them with healthy controls.

Methods: In this study, 25 patients with BSP, 22 patients with DED, and 23 healthy controls underwent resting-state functional magnetic resonance imaging (fMRI) scan. The amplitude of low-frequency fluctuations (ALFF) was applied to analyze the imaging data.

Results: Analysis of covariance (ANCOVA) revealed widespread differences in ALFF across the three groups. In comparison with healthy controls, patients with BSP showed abnormal ALFF in the sensorimotor integration related-brain regions, including the bilateral supplementary motor area (SMA), left cerebellar Crus I, left fusiform gyrus, bilateral superior medial prefrontal cortex (MPFC), and right superior frontal gyrus (SFG). In comparison with patients with DED, patients with BSP exhibited a significantly increased ALFF in the left cerebellar Crus I and left SMA. ALFF in the left fusiform gyrus/cerebellar Crus I was positively correlated with symptomatic severity of BSP.

Conclusions: Our results reveal that the distinctive changes in the brain function in patients with BSP are different from those in patients with DED and healthy controls. The results further emphasize the primary role of sensorimotor integration in the pathophysiology of BSP.

Cerebellar Theta Burst Stimulation on Walking Function in Stroke Patients: A Randomized Clinical Trial

Objectives: The objective of this study was to explore the efficacy of cerebellar intermittent theta burst stimulation (iTBS) on the walking function of stroke patients.

Methods: Stroke patients with walking dysfunction aged 25–80 years who had suffered their first unilateral stroke were included. A total of 36 patients [mean (SD) age, 53 (7.93) years; 10 women (28%)] were enrolled in the study. All participants received the same conventional physical therapy, including transfer, balance, and ambulation training, during admission for 50 min per day during 2 weeks (10 sessions). Every session was preceded by 3 min procedure of cerebellar iTBS applyed over the contralesional cerebellum in the intervention group or by a similar sham iTBS in control group. The groups were formed randomly and the baseline characteristics showed no significant difference. The primary outcome measure was Fugl–Meyer Assessment–Lower Extremity scores. Secondary outcomes included walking performance and corticospinal excitability. Measures were performed before the intervention beginning (T0), after the first (T1) and the second (T2) weeks.

Results: The Fugl–Meyer Assessment for lower extremity scores slightly improved with time in both groups with no significant difference between the groups and over the time. The walking performance significantly improved with time and between group. Two-way mixed measures ANOVA showed that there was significant interaction between time and group in comfortable walking time (F_2,68 = 6.5242, P = 0.0080, η²_partial = 0.276, ε = 0.641), between-group comparisons revealed significant differences at T1 (P = 0.0072) and T2 (P = 0.0133). The statistical analysis of maximum walking time showed that there was significant interaction between time and groups (F_2,68 = 5.4354, P = 0.0115, η²_partial = 0.198, ε = 0.734). Compared with T0, the differences of maximum walking time between the two groups at T1 (P = 0.0227) and T2 (P = 0.0127) were statistically significant. However, both the Timed up and go test and functional ambulation category scale did not yield significant differences between groups (P > 0.05).

Conclusion: Our results revealed that applying iTBS over the contralesional cerebellum paired with physical therapy could improve walking performance in patients after stroke, implying that cerebellar iTBS intervention may be a noninvasive strategy to promote walking function in these patients. This study was registered at ChiCTR, number ChiCTR1900026450.

A transcriptomic atlas of mouse cerebellar cortex comprehensively defines cell types

The cerebellar cortex is a well-studied brain structure with diverse roles in motor learning, coordination, cognition and autonomic regulation. However,  a complete inventory of cerebellar cell types is currently lacking. Here, using recent advances in high-throughput transcriptional profiling^1–3, we molecularly define cell types across individual lobules of the adult mouse cerebellum. Purkinje neurons showed considerable regional specialization, with the greatest diversity occurring in the posterior lobules. For several types of cerebellar interneuron, the molecular variation within each type was more continuous, rather than discrete. In particular, for the unipolar brush cells—an interneuron population previously subdivided into discrete populations—the continuous variation in gene expression was associated with a graded continuum of electrophysiological properties. Notably, we found that molecular layer interneurons were composed of two molecularly and functionally distinct types. Both types show a continuum of morphological variation through the thickness of the molecular layer, but electrophysiological recordings revealed marked differences between the two types in spontaneous firing, excitability and electrical coupling. Together, these findings provide a comprehensive cellular atlas of the cerebellar cortex, and outline a methodological and conceptual framework for the integration of molecular, morphological and physiological ontologies for defining brain cell types.

A comprehensive atlas of cell types and regional specializations in the mouse cerebellar cortex.

GluA4 facilitates cerebellar expansion coding and enables associative memory formation

AMPA receptors (AMPARs) mediate excitatory neurotransmission in the central nervous system (CNS) and their subunit composition determines synaptic efficacy. Whereas AMPAR subunits GluA1–GluA3 have been linked to particular forms of synaptic plasticity and learning, the functional role of GluA4 remains elusive. Here, we demonstrate a crucial function of GluA4 for synaptic excitation and associative memory formation in the cerebellum. Notably, GluA4-knockout mice had ~80% reduced mossy fiber to granule cell synaptic transmission. The fidelity of granule cell spike output was markedly decreased despite attenuated tonic inhibition and increased NMDA receptor-mediated transmission. Computational network modeling incorporating these changes revealed that deletion of GluA4 impairs granule cell expansion coding, which is important for pattern separation and associative learning. On a behavioral level, while locomotor coordination was generally spared, GluA4-knockout mice failed to form associative memories during delay eyeblink conditioning. These results demonstrate an essential role for GluA4-containing AMPARs in cerebellar information processing and associative learning.

Bidirectional learning in upbound and downbound microzones of the cerebellum

Over the past several decades, theories about cerebellar learning have evolved. A relatively simple view that highlighted the contribution of one major form of heterosynaptic plasticity to cerebellar motor learning has given way to a plethora of perspectives that suggest that many different forms of synaptic and non-synaptic plasticity, acting at various sites, can control multiple types of learning behaviour. However, there still seem to be contradictions between the various hypotheses with regard to the mechanisms underlying cerebellar learning. The challenge is therefore to reconcile these different views and unite them into a single overall concept. Here I review our current understanding of the changes in the activity of cerebellar Purkinje cells in different 'microzones' during various forms of learning. I describe an emerging model that indicates that the activity of each microzone is bound to either increase or decrease during the initial stages of learning, depending on the directional and temporal demands of its downstream circuitry and the behaviour involved.

Microglia-Triggered Plasticity of Intrinsic Excitability Modulates Psychomotor Behaviors in Acute Cerebellar Inflammation

Cerebellar dysfunction relates to various psychiatric disorders, including autism spectrum and depressive disorders. However, the physiological aspect is less advanced. Here, we investigate the immune-triggered hyperexcitability in the cerebellum on a wider scope. Activated microglia via exposure to bacterial endotoxin lipopolysaccharide or heat-killed Gram-negative bacteria induce a potentiation of the intrinsic excitability in Purkinje neurons, which is suppressed by microglia-activity inhibitor and microglia depletion. An inflammatory cytokine, tumor necrosis factor alpha (TNF-α), released from microglia via toll-like receptor 4, triggers this plasticity. Our two-photon FRET ATP imaging shows an increase in ATP concentration following endotoxin exposure. Both TNF-α and ATP secretion facilitate synaptic transmission. Region-specific inflammation in the cerebellum in vivo shows depression- and autistic-like behaviors. Furthermore, both TNF-α inhibition and microglia depletion revert such behavioral abnormality. Resting-state functional MRI reveals overconnectivity between the inflamed cerebellum and the prefrontal neocortical regions. Thus, immune activity in the cerebellum induces neuronal hyperexcitability and disruption of psychomotor behaviors in animals.

Response to Hypoxic Preconditioning of Glial Cells from the Roof of the Fourth Ventricle

The cerebellum harbors a specialized area on the roof of the fourth ventricle that is composed of glial cells and neurons that interface with the cerebrospinal fluid. This region includes the so-called ventromedial cord (VMC), which is composed of cells that are glial fibrillary acidic protein (GFAP)-positive and nestin-positive and distributes along the midline in association with blood vessels. We hypothesized that these cells should compare to GFAP and nestin-positive cells that are known to exist in other areas of the brain, which undergo proliferation and differentiation under hypoxic conditions. Thus, we tested whether cells of the VMC would display a similar reaction to hypoxic preconditioning (HPC). Indeed, we found that the VMC does respond to HPC by reorganizing its cellular components before it gradually returns to its basal state after about a week. This response we documented by monitoring global changes in the expression of GFAP-EGFP in transgenic mice, using light-sheet fluorescence microscopy (LSFM) revealed a dramatic loss of EGFP upon HPC, and was paralleled by retraction of Bergmann glial cell processes. This EGFP loss was supported by western blot analysis, which also showed a loss in the astrocyte-markers GFAP and ALDH1L1. On the other hand, other cell-markers appeared to be upregulated in the blots (including nestin, NeuN, and Iba1). Finally, we found that HPC does not remarkably affect the incorporation of BrdU into cells on the cerebellum, but strongly augments BrdU incorporation into periventricular cells on the floor of the fourth ventricle over the adjacent medulla.

Functionally distinct Purkinje cell types show temporal precision in encoding locomotion

Purkinje cells, the principal neurons of cerebellar computations, are believed to comprise a uniform neuronal population of cells, each with similar functional properties. Here, we show an undiscovered heterogeneity of adult zebrafish Purkinje cells, revealing the existence of anatomically and functionally distinct cell types. Dual patch-clamp recordings showed that the cerebellar circuit contains all Purkinje cell types that cross-communicate extensively using chemical and electrical synapses. Further activation of spinal central pattern generators (CPGs) revealed unique phase-locked activity from each Purkinje cell type during the locomotor cycle. Thus, we show intricately organized Purkinje cell networks in the adult zebrafish cerebellum that encode the locomotion rhythm differentially, and we suggest that these organizational properties may also apply to other cerebellar functions.

Synergistic excitability plasticity in cerebellar functioning

The cerebellum, a universal processor for sensory acquisition and internal models, and its association with synaptic and nonsynaptic plasticity have been envisioned as the biological correlates of learning, perception, and even thought. Indeed, the cerebellum is no longer considered merely as the locus of motor coordination and its learning. Here, we introduce the mechanisms underlying the induction of multiple types of plasticity in cerebellar circuit and give an overview focusing on the plasticity of nonsynaptic intrinsic excitability. The discovery of long-term potentiation of synaptic responsiveness in hippocampal neurons led investigations into changes of their intrinsic excitability. This activity-dependent potentiation of neuronal excitability is distinct from that of synaptic efficacy. Systematic examination of excitability plasticity has indicated that the modulation of various types of Ca²⁺ - and voltage-dependent K⁺ channels underlies the phenomenon, which is also triggered by immune activity. Intrinsic plasticity is expressed specifically on dendrites and modifies the integrative processing and filtering effect. In Purkinje cells, modulation of the discordance of synaptic current on soma and dendrite suggested a novel type of cellular learning mechanism. This property enables a plausible synergy between synaptic efficacy and intrinsic excitability, by amplifying electrical conductivity and influencing the polarity of bidirectional synaptic plasticity. Furthermore, the induction of intrinsic plasticity in the cerebellum correlates with motor performance and cognitive processes, through functional connections from the cerebellar nuclei to neocortex and associated regions: for example, thalamus and midbrain. Taken together, recent advances in neuroscience have begun to shed light on the complex functioning of nonsynaptic excitability and the synergy.

Evidence for Hierarchical Cognitive Control in the Human Cerebellum

In non-habitual situations, cognitive control aligns actions with both short- and long-term goals. The capacity for cognitive control is tightly tied to the prefrontal cortex, whose expansion in humans relative to other species is thought to support our superior cognitive control. However, the posterolateral cerebellum has also expanded greatly relative to non-human primates and has an organizational structure that mirrors the prefrontal cortex. Nevertheless, cerebellar contributions to cognitive control are poorly understood. Here, we sought to explore whether a functional hierarchical processing framework, applied to the cerebellum, could elucidate cerebellar contributions to cognitive control. Using functional magnetic resonance imaging, we show that a gradient within the posterolateral cerebellum supports cognitive control with motor-adjacent cerebellar sub-regions supporting control of concrete, proximal actions and motor-distal, cerebellar sub-regions supporting abstract, future processing. This gradient was functionally hierarchical, with regions higher in the hierarchy influencing the relationship between regions lower in the hierarchy. This functional hierarchy provides the infrastructure by which context can inform current actions and prepare for future goals. Crucially, this mirrors the hierarchical organization of cognitive control within the prefrontal cortex. Based on these findings, we propose that the cerebellum contains within itself a parallel but separate hierarchical organization that, along with the prefrontal cortex, supports complex cognition.

Gradients in the mammalian cerebellar cortex enable Fourier-like transformation and improve storing capacity

Cerebellar granule cells (GCs) make up the majority of all neurons in the vertebrate brain, but heterogeneities among GCs and potential functional consequences are poorly understood. Here, we identified unexpected gradients in the biophysical properties of GCs in mice. GCs closer to the white matter (inner-zone GCs) had higher firing thresholds and could sustain firing with larger current inputs than GCs closer to the Purkinje cell layer (outer-zone GCs). Dynamic Clamp experiments showed that inner- and outer-zone GCs preferentially respond to high- and low-frequency mossy fiber inputs, respectively, enabling dispersion of the mossy fiber input into its frequency components as performed by a Fourier transformation. Furthermore, inner-zone GCs have faster axonal conduction velocity and elicit faster synaptic potentials in Purkinje cells. Neuronal network modeling revealed that these gradients improve spike-timing precision of Purkinje cells and decrease the number of GCs required to learn spike-sequences. Thus, our study uncovers biophysical gradients in the cerebellar cortex enabling a Fourier-like transformation of mossy fiber inputs.

Online polarity-dependent effects of cerebellar transcranial direct current stimulation on motor speed and fine manual dexterity. A randomized controlled trial

OBJECTIVES

To investigate the role of cerebellar transcranial direct current stimulation (ctDCS) in modulating cerebellar functions in the motor domains of fine motor dexterity and motor speed. Methods: A single-blind, randomized sham-controlled study was conducted between January and July 2018 at the neuroscience laboratory of Imam Abdulrahman Bin Faisal University. A total of 63 healthy participants were assessed for eligibility. Sixty subjects met the criteria of the study and were randomly divided into 3 groups that received anodal, cathodal or sham ctDCS. Subjects performed 2 motor tasks, The Grooved Pegboard test (GPT) assessed fine manual dexterity and the Finger Tapping Task (FTT) assessed motor speed. Subjects undertook the 2 tasks in a single intervention session while 20 minutes of 2mA ctDCS was administered online. The short form of the Edinburgh Handedness Inventory was used to assess handedness and both tasks were performed first with the dominant and then the non-dominant hand. The primary outcome measures included the time of completion of GPT for fine manual dexterity and the mean number of finger-taps for motor speed of each hand. Results: ANOVA revealed a highly significant polarity dependent Group*Task interaction (p less than 0.01) for FTT scores. ANOVA also revealed a non-significant Group*Task interaction for GPT scores.  Conclusion: Findings indicate that ctDCS has a modulatory effect on motor speed and could be a promising therapeutic intervention for treatment of neurological conditions with motor deficits.

Life without a brain: Neuroradiological and behavioral evidence of neuroplasticity necessary to sustain brain function in the face of severe hydrocephalus

A two-year old rat, R222, survived a life-time of extreme hydrocephaly affecting the size and organization of its brain. Much of the cortex was severely thinned and replaced by cerebrospinal fluid, yet R222 had normal motor function, could hear, see, smell, and respond to tactile stimulation. The hippocampus was malformed and compressed into the lower hindbrain together with the hypothalamus midbrain and pons, yet R222 showed normal spatial memory as compared to age-matched controls. BOLD MRI was used to study the reorganization of R222’s brain function showing global activation to visual, olfactory and tactile stimulation, particularly in the brainstem/cerebellum. The results are discussed in the context of neuroadaptation in the face of severe hydrocephaly and subsequent tissue loss, with an emphasis on what is the “bare minimum” for survival.

Evidence of Neurobiological Changes in the Presymptomatic PINK1 Knockout Rat

BACKGROUND

Genetic models of Parkinson's disease (PD) coupled with advanced imaging techniques can elucidate neurobiological disease progression, and can help identify early biomarkers before clinical signs emerge. PTEN-induced putative kinase 1 (PINK1) helps protect neurons from mitochondrial dysfunction, and a mutation in the associated gene is a risk factor for recessive familial PD. The PINK1 knockout (KO) rat is a novel model for familial PD that has not been neuroradiologically characterized for alterations in brain structure/function, alongside behavior, prior to 4 months of age.

OBJECTIVE

To identify biomarkers of presymptomatic PD in the PINK1 -/- rat at 3 months using magnetic resonance imaging techniques.

METHODS

At postnatal weeks 12-13; one month earlier than previously reported signs of motor and cognitive dysfunction, this study combined imaging modalities, including assessment of quantitative anisotropy across 171 individual brain areas using an annotated MRI rat brain atlas to identify sites of gray matter alteration between wild-type and PINK1 -/- rats.

RESULTS

The olfactory system, hypothalamus, thalamus, nucleus accumbens, and cerebellum showed differences in anisotropy between experimental groups. Molecular analyses revealed reduced levels of glutathione, ATP, and elevated oxidative stress in the substantia nigra, striatum and deep cerebellar nuclei. Mitochondrial genes encoding proteins in Complex IV, along with mRNA levels associated with mitochondrial function and genes involved in glutathione synthesis were reduced. Differences in brain structure did not align with any cognitive or motor impairment.

CONCLUSIONS

These data reveal early markers, and highlight novel brain regions involved in the pathology of PD in the PINK1 -/- rat before behavioral dysfunction occurs.

Neuroradiological Changes Following Single or Repetitive Mild TBI

Objectives

To test the hypothesis that there are differences in neuroradiological measures between single and repeated mild traumatic brain injury using multimodal MRI.

Methods

A closed-head momentum exchange model was used to produce one or three mild head injuries in young adult male rats compared to non-injured, age and weight-matched controls. Six-seven weeks post-injury, rats were studied for deficits in cognitive and motor function. Seven-eight weeks post-injury changes in brain anatomy and function were evaluated through analysis of high resolution T2 weighted images, resting-state BOLD functional connectivity, and diffusion weighted imaging with quantitative anisotropy.

Results

Head injuries occurred without skull fracture or signs of intracranial bleeding or contusion. There were no significant differences in cognitive or motors behaviors between experimental groups. With a single mild hit, the affected areas were limited to the caudate/putamen and central amygdala. Rats hit three times showed altered diffusivity in white matter tracts, basal ganglia, central amygdala, brainstem, and cerebellum. Comparing three hits to one hit showed a similar pattern of change underscoring a dose effect of repeated head injury on the brainstem and cerebellum. Disruption of functional connectivity was pronounced with three mild hits. The midbrain dopamine system, hippocampus, and brainstem/cerebellum showed hypoconnectivity. Interestingly, rats exposed to one hit showed enhanced functional connectivity (or hyperconnectivity) across brain sites, particularly between the olfactory system and the cerebellum.

Interpretation

Neuroradiological evidence of altered brain structure and function, particularly in striatal and midbrain dopaminergic areas, persists long after mild repetitive head injury. These changes may serve as biomarkers of neurodegeneration and risk for dementia later in life.

The generation of granule cells during the development and evolution of the cerebellum

The cerebellum coordinates vestibular input into the hindbrain to control balance and movement, and its anatomical complexity is increasingly viewed as a high-throughput processing center for sensory and cognitive functions. Cerebellum development however is relatively simple, and arises from a specialized structure in the anterior hindbrain called the rhombic lip, which along with the ventricular zone of the rostral-most dorsal hindbrain region, give rise to the distinct cell types that constitute the cerebellum. Granule cells, being the most numerous cell types, arise from the rhombic lip and form a dense and distinct layer of the cerebellar cortex. In this short review, we describe the various strategies used by amniotes and anamniotes to generate and diversify granule cell types during cerebellar development.

The role of the cerebellum in adaptation: ALE meta-analyses on sensory feedback error

It is widely accepted that unexpected sensory consequences of self‐action engage the cerebellum. However, we currently lack consensus on where in the cerebellum, we find fine‐grained differentiation to unexpected sensory feedback. This may result from methodological diversity in task‐based human neuroimaging studies that experimentally alter the quality of self‐generated sensory feedback. We gathered existing studies that manipulated sensory feedback using a variety of methodological approaches and performed activation likelihood estimation (ALE) meta‐analyses. Only half of these studies reported cerebellar activation with considerable variation in spatial location. Consequently, ALE analyses did not reveal significantly increased likelihood of activation in the cerebellum despite the broad scientific consensus of the cerebellum's involvement. In light of the high degree of methodological variability in published studies, we tested for statistical dependence between methodological factors that varied across the published studies. Experiments that elicited an adaptive response to continuously altered sensory feedback more frequently reported activation in the cerebellum than those experiments that did not induce adaptation. These findings may explain the surprisingly low rate of significant cerebellar activation across brain imaging studies investigating unexpected sensory feedback. Furthermore, limitations of functional magnetic resonance imaging to probe the cerebellum could play a role as climbing fiber activity associated with feedback error processing may not be captured by it. We provide methodological recommendations that may guide future studies.

Neuronal Regulation of Fast Synaptotagmin Isoforms Controls the Relative Contributions of Synchronous and Asynchronous Release

Neurotransmitter release can be synchronous and occur within milliseconds of action potential invasion, or asynchronous and persist for tens of milliseconds. The molecular determinants of release kinetics remain poorly understood. It has been hypothesized that asynchronous release dominates when fast Synaptotagmin isoforms are far from calcium channels or when specialized sensors, such as Synaptotagmin 7, are abundant. Here we test these hypotheses for GABAergic projections onto neurons of the inferior olive, where release in different subnuclei ranges from synchronous to asynchronous. Surprisingly, neither of the leading hypotheses accounts for release kinetics. Instead, we find that rapid Synaptotagmin isoforms are abundant in subnuclei with synchronous release but absent where release is asynchronous. Viral expression of Synaptotagmin 1 transforms asynchronous synapses into synchronous ones. Thus, the nervous system controls levels of fast Synaptotagmin isoforms to regulate release kinetics and thereby controls the ability of synapses to encode spike rates or precise timing.

Motor context dominates output from purkinje cell functional regions during reflexive visuomotor behaviours

The cerebellum integrates sensory stimuli and motor actions to enable smooth coordination and motor learning. Here we harness the innate behavioral repertoire of the larval zebrafish to characterize the spatiotemporal dynamics of feature coding across the entire Purkinje cell population during visual stimuli and the reflexive behaviors that they elicit. Population imaging reveals three spatially-clustered regions of Purkinje cell activity along the rostrocaudal axis. Complementary single-cell electrophysiological recordings assign these Purkinje cells to one of three functional phenotypes that encode a specific visual, and not motor, signal via complex spikes. In contrast, simple spike output of most Purkinje cells is strongly driven by motor-related tail and eye signals. Interactions between complex and simple spikes show heterogeneous modulation patterns across different Purkinje cells, which become temporally restricted during swimming episodes. Our findings reveal how sensorimotor information is encoded by individual Purkinje cells and organized into behavioral modules across the entire cerebellum.

Depressed by Learning-Heterogeneity of the Plasticity Rules at Parallel Fiber Synapses onto Purkinje Cells

Climbing fiber-driven long-term depression (LTD) of parallel fiber synapses onto cerebellar Purkinje cells has long been investigated as a putative mechanism of motor learning. We recently discovered that the rules governing the induction of LTD at these synapses vary across different regions of the cerebellum. Here, we discuss the design of LTD induction protocols in light of this heterogeneity in plasticity rules. The analytical advantages of the cerebellum provide an opportunity to develop a deeper understanding of how the specific plasticity rules at synapses support the implementation of learning.

The role of the cerebellum in drug-cue associative memory: functional interactions with the medial prefrontal cortex

Drug-induced Pavlovian memories are thought to be crucial for drug addiction because they guide behaviour towards environments with drug availability. Drug-related memory depends on persistent changes in dopamine-glutamate interactions in the medial prefrontal cortex (mPFC), basolateral amygdala, nucleus accumbens core and hippocampus. Recent evidence from our laboratory indicated that the cerebellum is also a relevant node for drug-cue associations. In the present study, we tested the role that specific regions of the cerebellum and mPFC play in the acquisition of cocaine-induced preference conditioning. Quinolinic acid was used to manage a permanent deactivation of lobule VIII in the vermis prior to conditioning. Additionally, lidocaine was infused into the prelimbic and infralimbic (IL) cortices for reversible deactivation before every training session. The present findings show, for the first time, that the cerebellum and mPFC might act together in order to acquire drug-cue Pavlovian associations. Either a dorsal lesion in lobule VIII or an IL deactivation encouraged cocaine-induced preference conditioning. Moreover, simultaneous IL-cerebellar deactivation prevented the effect of either of the separate deactivations. Therefore, similar to the IL cortex, neural activity in the cerebellum may be crucial for ensuring inhibitory control of the expression of cocaine-related memories.

The basal interstitial nucleus (BIN) of the cerebellum provides diffuse ascending inhibitory input to the floccular granule cell layer

The basal interstitial nucleus (BIN) in the white matter of the vestibulocerebellum has been defined more than three decades ago, but has since been largely ignored. It is still unclear which neurotransmitters are being used by BIN neurons, how these neurons are connected to the rest of the brain and what their activity patterns look like. Here, we studied BIN neurons in a range of mammals, including macaque, human, rat, mouse, rabbit, and ferret, using tracing, immunohistological and electrophysiological approaches. We show that BIN neurons are GABAergic and glycinergic, that in primates they also express the marker for cholinergic neurons choline acetyl transferase (ChAT), that they project with beaded fibers to the glomeruli in the granular layer of the ipsilateral floccular complex, and that they are driven by excitation from the ipsilateral and contralateral medio-dorsal medullary gigantocellular reticular formation. Systematic analysis of codistribution of the inhibitory synapse marker VIAAT, BIN axons, and Golgi cell marker mGluR2 indicate that BIN axon terminals complement Golgi cell axon terminals in glomeruli, accounting for a considerable proportion ( > 20%) of the inhibitory terminals in the granule cell layer of the floccular complex. Together, these data show that BIN neurons represent a novel and relevant inhibitory input to the part of the vestibulocerebellum that controls compensatory and smooth pursuit eye movements.

UPR activation specifically modulates glutamate neurotransmission in the cerebellum of a mouse model of autism

An increasing number of rare mutations linked to autism spectrum disorders have been reported in genes encoding for proteins involved in synapse formation and maintenance, such as the post-synaptic cell adhesion proteins neuroligins. Most of the autism-linked mutations in the neuroligin genes map on the extracellular protein domain. The autism-linked substitution R451C in Neuroligin3 (NLGN3) induces a local misfolding of the extracellular domain, causing defective trafficking and retention of the mutant protein in the endoplasmic reticulum (ER). The activation of the unfolded protein response (UPR), due to misfolded proteins accumulating in the ER, has been implicated in pathological and physiological conditions of the nervous system. It was previously shown that the over-expression of R451C NLGN3 in a cellular system leads to the activation of the UPR. Here, we have investigated whether this protective cellular response is detectable in the knock-in mouse model of autism endogenously expressing R451C NLGN3. Our data showed up-regulation of UPR markers uniquely in the cerebellum of the R451C mice compared to WT littermates, at both embryonic and adult stages, but not in other brain regions. Miniature excitatory currents in the Purkinje cells of the R451C mice showed higher frequency than in the WT, which was rescued inhibiting the PERK branch of UPR. Taken together, our data indicate that the R451C mutation in neuroligin3 elicits UPR in vivo, which appears to trigger alterations of synaptic function in the cerebellum of a mouse model expressing the R451C autism-linked mutation.

Surface-based characteristics of the cerebellar cortex visualized with ultra-high field MRI

Although having a relatively homogeneous cytoarchitectonic organization, the cerebellar cortex is a heterogeneous region characterized by different amounts of myelin, iron and protein expression profiles. In this study, we used quantitative T₁ and T₂* mapping at ultra-high field (7T) MRI to investigate the tissue characteristics of the cerebellar gray matter surface and its layers. Detailed subject-specific surfaces were generated at three different cortical depths and averaged across subjects to create averaged T₁- and T₂*-maps on the cerebellar surface. T₁ surfaces showed an alternation of lower and higher T₁ values when going from the median to the lateral part of the cerebellar hemispheres. In addition, longer T₁ values were observed in the more superficial gray matter layers. T₂*-maps showed a similar longitudinal pattern, but no change related to the cortical depths. These patterns are possibly due to variations in the level of myelination, iron and zebrin protein expression.

Regional differences in Purkinje cell morphology in the cerebellar vermis of male mice

Regional differences in dendritic architecture can influence connectivity and dendritic signal integration, with possible consequences for neuronal computation. In the cerebellum, analyses of Purkinje cells (PCs), which are functionally critical as they provide the sole output of the cerebellar cortex, have suggested that the cerebellar cortex is not uniform in structure as traditionally assumed. However, the limitations of traditional staining methods and microscopy capabilities have presented difficulties in investigating possible local variations in PC morphology. To address this question, we used male mice expressing green fluorescent protein selectively in PCs. Using Neurolucida 360 with confocal image stacks, we reconstructed dendritic arbors of PCs residing in lobule V (anterior) and lobule IX (posterior) of the vermis. We then analyzed morphologies of individual arbors and the structure of the assembled "jungle," comparing these features across anatomical locations and age groups. Strikingly, we found that in lobule IX, half of the reconstructed PCs had two primary dendrites emanating from their soma, whereas fewer than a quarter showed this characteristic in lobule V. Furthermore, PCs in lobule V showed more efficient spatial occupancy compared to lobule IX, as well as greater packing density and increased arbor overlap in the adult. When analyzing complete ensembles of PC arbors, we also observed "hot spots" of increased dendritic density in lobule V, whereas lobule IX showed a more homogeneous spread of dendrites. These differences suggest that input patterns and/or physiology of PCs could likewise differ along the vermis, with possible implications for cerebellar function.

Delineation of Subregions in the Early Postnatal Human Cerebellum for Design-Based Stereologic Studies

Recent design-based stereologic studies have shown that the early postnatal (<1 year of age) human cerebellum is characterized by very high plasticity and may thus be very sensitive to external and internal influences during the first year of life. A potential weakness of these studies is that they were not separately performed on functionally relevant subregions of the cerebellum, as was the case in a few design-based stereologic studies on the adult human cerebellum. The aim of the present study was to assess whether it is possible to identify unequivocally the primary, superior posterior, horizontal, ansoparamedian, and posterolateral fissures in the early postnatal human cerebellum, based on which functionally relevant subregions could be delineated. This was tested in 20 human post mortem cerebellar halves from subjects aged between 1 day and 11 months by means of a combined macroscopic and microscopic approach. We found that the superior posterior, horizontal, and posterolateral fissures can be reliably identified on all of the specimens. However, reliable and reproducible identification of the primary and ansoparamedian fissures was not possible. Accordingly, it appears feasible to perform subregion-specific investigations in the early postnatal human cerebellum when the identification of subregions is restricted to crus I (bordered by the superior posterior and horizontal fissures) and the flocculus (bordered by the posterolateral fissure). As such, it is recommended to define the entire cerebellar cortex as the region of interest in design-based stereologic studies on the early postnatal human cerebellum to guarantee reproducibility of results.

Purkinje Cells Directly Inhibit Granule Cells in Specialized Regions of the Cerebellar Cortex

Inhibition of granule cells plays a key role in gating the flow of signals into the cerebellum, and it is thought that Golgi cells are the only interneurons that inhibit granule cells. Here we show that Purkinje cells, the sole output neurons of the cerebellar cortex, also directly inhibit granule cells via their axon collaterals. Anatomical and optogenetic studies indicate that this non-canonical feedback is region specific: it is most prominent in lobules that regulate eye movement and process vestibular information. Collaterals provide fast, slow, and tonic inhibition to granule cells, and thus allow Purkinje cells to regulate granule cell excitability on multiple timescales. We propose that this feedback mechanism could regulate excitability of the input layer, contribute to sparse coding, and mediate temporal integration.

Inverse Stochastic Resonance in Cerebellar Purkinje Cells

Purkinje neurons play an important role in cerebellar computation since their axons are the only projection from the cerebellar cortex to deeper cerebellar structures. They have complex internal dynamics, which allow them to fire spontaneously, display bistability, and also to be involved in network phenomena such as high frequency oscillations and travelling waves. Purkinje cells exhibit type II excitability, which can be revealed by a discontinuity in their f-I curves. We show that this excitability mechanism allows Purkinje cells to be efficiently inhibited by noise of a particular variance, a phenomenon known as inverse stochastic resonance (ISR). While ISR has been described in theoretical models of single neurons, here we provide the first experimental evidence for this effect. We find that an adaptive exponential integrate-and-fire model fitted to the basic Purkinje cell characteristics using a modified dynamic IV method displays ISR and bistability between the resting state and a repetitive activity limit cycle. ISR allows the Purkinje cell to operate in different functional regimes: the all-or-none toggle or the linear filter mode, depending on the variance of the synaptic input. We propose that synaptic noise allows Purkinje cells to quickly switch between these functional regimes. Using mutual information analysis, we demonstrate that ISR can lead to a locally optimal information transfer between the input and output spike train of the Purkinje cell. These results provide the first experimental evidence for ISR and suggest a functional role for ISR in cerebellar information processing.

How neurons generate output spikes in response to various combinations of inputs is a central issue in contemporary neuroscience. Due to their large dendritic tree and complex intrinsic properties, cerebellar Purkinje cells are an important model system to study this input-output transformation. Here we examine how noise can change the parameters of this transformation. In experiments we found that spike generation in Purkinje cells can be efficiently inhibited by noise of a particular amplitude. This effect is called inverse stochastic resonance (ISR) and has previously been described only in theoretical models of neurons. We explain the mechanism underlying ISR using a simple model matching the properties of experimentally characterized Purkinje cells. We found that ISR is present in Purkinje cells when the mean input current is near threshold for spike generation. ISR can be explained by the co-existence of resting and spiking solutions of the simple model. Changes of the input noise variance change the lifetime of these resting and spiking states, suggesting a mechanism for a tunable filter with long time constants implemented by a Purkinje cell population in the cerebellum. Finally, ISR leads to locally optimal information transfer from the input to the output of a Purkinje cell.

Cerebellar contributions to motor control and language comprehension: searching for common computational principles

The past 25 years have seen the functional domain of the cerebellum extend beyond the realm of motor control, with considerable discussion of how this subcortical structure contributes to cognitive domains including attention, memory, and language. Drawing on evidence from neuroanatomy, physiology, neuropsychology, and computational work, sophisticated models have been developed to describe cerebellar function in sensorimotor control and learning. In contrast, mechanistic accounts of how the cerebellum contributes to cognition have remained elusive. Inspired by the homogeneous cerebellar microanatomy and a desire for parsimony, many researchers have sought to extend mechanistic ideas from motor control to cognition. One influential hypothesis centers on the idea that the cerebellum implements internal models, representations of the context-specific dynamics of an agent's interactions with the environment, enabling predictive control. We briefly review cerebellar anatomy and physiology, to review the internal model hypothesis as applied in the motor domain, before turning to extensions of these ideas in the linguistic domain, focusing on speech perception and semantic processing. While recent findings are consistent with this computational generalization, they also raise challenging questions regarding the nature of cerebellar learning, and may thus inspire revisions of our views on the role of the cerebellum in sensorimotor control.

Does Transcranial Alternating Current Stimulation Induce Cerebellum Plasticity? Feasibility, Safety and Efficacy of a Novel Electrophysiological Approach

BACKGROUND

Cerebellum-brain functional connectivity can be shaped through different non-invasive neurostimulation approaches. In this study, we propose a novel approach to perturb the cerebellum-brain functional connectivity by means of transcranial alternating current stimulation (tACS).

METHODS

Twenty-five healthy individuals underwent a cerebellar tACS protocol employing different frequencies (10, 50, and 300 Hz) and a sham-tACS over the right cerebellar hemisphere. We measured their after-effects on the motor evoked potential (MEP) amplitude, the cerebellum-brain inhibition (CBI), the long-latency intracortical inhibition (LICI), from the primary motor cortex of both the hemispheres. In addition, we assessed the functional adaptation to a right hand sequential tapping motor task.

RESULTS

None of the participants had any side-effect. Following 50 Hz-tACS, we observed a clear contralateral CBI weakening, paralleled by a MEP increase with a better adaptation to frequency variations during the sequential tapping. The 300 Hz-tACS induced a contralateral CBI strengthening, without significant MEP and kinematic after-effects. The 10 Hz-tACS conditioning was instead ineffective.

CONCLUSIONS

We may argue that tACS protocols could have interfered with the activity of CBI-sustaining Purkinje cell, affecting motor adaptation. Our safe approach seems promising in studying the cerebellum-brain functional connectivity, with possible implications in neurorehabilitative settings.