What the cerebellum computes

Functional mapping of the somatosensory cortex using noninvasive fMRI and touch in awake dogs

Dogs are increasingly used as a model for neuroscience due to their ability to undergo functional MRI fully awake and unrestrained, after extensive behavioral training. Still, we know rather little about dogs' basic functional neuroanatomy, including how basic perceptual and motor functions are localized in their brains. This is a major shortcoming in interpreting activations obtained in dog fMRI. The aim of this preregistered study was to localize areas associated with somatosensory processing. To this end, we touched N = 22 dogs undergoing fMRI scanning on their left and right flanks using a wooden rod. We identified activation in anatomically defined primary and secondary somatosensory areas (SI and SII), lateralized to the contralateral hemisphere depending on the side of touch, and importantly also activation beyond SI and SII, in the cingulate cortex, right cerebellum and vermis, and the sylvian gyri. These activations may partly relate to motor control (cerebellum, cingulate), but also potentially to higher-order cognitive processing of somatosensory stimuli (rostral sylvian gyri), and the affective aspects of the stimulation (cingulate). We also found evidence for individual side biases in a vast majority of dogs in our sample, pointing at functional lateralization of somatosensory processing. These findings not only provide further evidence that fMRI is suited to localize neuro-cognitive processing in dogs, but also expand our understanding of in vivo touch processing in mammals, beyond classically defined primary and secondary somatosensory cortices.

Local synaptic inhibition mediates cerebellar granule cell pattern separation and enables learned sensorimotor associations

The cerebellar cortex has a key role in generating predictive sensorimotor associations. To do so, the granule cell layer is thought to establish unique sensorimotor representations for learning. However, how this is achieved and how granule cell population responses contribute to behavior have remained unclear. To address these questions, we have used in vivo calcium imaging and granule cell-specific pharmacological manipulation of synaptic inhibition in awake, behaving mice. These experiments indicate that inhibition sparsens and thresholds sensory responses, limiting overlap between sensory ensembles and preventing spiking in many granule cells that receive excitatory input. Moreover, inhibition can be recruited in a stimulus-specific manner to powerfully decorrelate multisensory ensembles. Consistent with these results, granule cell inhibition is required for accurate cerebellum-dependent sensorimotor behavior. These data thus reveal key mechanisms for granule cell layer pattern separation beyond those envisioned by classical models.

Neurophysiological evidence of sensory prediction errors driving speech sensorimotor adaptation

The human sensorimotor system has a remarkable ability to quickly and efficiently learn movements from sensory experience. A prominent example is sensorimotor adaptation, learning that characterizes the sensorimotor system's response to persistent sensory errors by adjusting future movements to compensate for those errors. Despite being essential for maintaining and fine-tuning motor control, mechanisms underlying sensorimotor adaptation remain unclear. A component of sensorimotor adaptation is implicit (i.e., the learner is unaware of the learning process) which has been suggested to result from sensory prediction errors-the discrepancies between predicted sensory consequences of motor commands and actual sensory feedback. However, to date no direct neurophysiological evidence that sensory prediction errors drive adaptation has been demonstrated. Here, we examined prediction errors via magnetoencephalography (MEG) imaging of the auditory cortex during sensorimotor adaptation of speech to altered auditory feedback, an entirely implicit adaptation task. Specifically, we measured how speaking-induced suppression (SIS)--a neural representation of auditory prediction errors--changed over the trials of the adaptation experiment. SIS refers to the suppression of auditory cortical response to speech onset (in particular, the M100 response) to self-produced speech when compared to the response to passive listening to identical playback of that speech. SIS was reduced (reflecting larger prediction errors) during the early learning phase compared to the initial unaltered feedback phase. Furthermore, reduction in SIS positively correlated with behavioral adaptation extents, suggesting that larger prediction errors were associated with more learning. In contrast, such a reduction in SIS was not found in a control experiment in which participants heard unaltered feedback and thus did not adapt. In addition, in some participants who reached a plateau in the late learning phase, SIS increased (reflecting smaller prediction errors), demonstrating that prediction errors were minimal when there was no further adaptation. Together, these findings provide the first neurophysiological evidence for the hypothesis that prediction errors drive human sensorimotor adaptation.

Cerebellar associative learning underlies skilled reach adaptation

The cerebellum is hypothesized to refine movement through online adjustments. We examined how such predictive control may be generated using a mouse reach paradigm, testing whether the cerebellum uses within-reach information as a predictor to adjust reach kinematics. We first identified a population-level response in Purkinje cells that scales inversely with reach velocity, pointing to the cerebellar cortex as a potential site linking kinematic predictors and anticipatory control. Next, we showed that mice can learn to compensate for a predictable reach perturbation caused by repeated, closed-loop optogenetic stimulation of pontocerebellar mossy fiber inputs. Both neural and behavioral readouts showed adaptation to position-locked mossy fiber perturbations and exhibited aftereffects when stimulation was removed. Surprisingly, position-randomized stimulation schedules drove partial adaptation but no opposing aftereffects. A model that recapitulated these findings suggests that the cerebellum may decipher cause-and-effect relationships through time-dependent generalization mechanisms.

Oral lipid-based formulations alter delivery of cannabidiol to different anatomical regions in the brain

Delivery to the brain is a challenging task due to its protection by the blood-brain barrier (BBB). Lipids and fatty acids are reported to affect the permeability of the BBB, although this has not been reported following oral administration. Cannabidiol (CBD) has high therapeutic potential in the brain, therefore, this work investigated CBD delivery to anatomical brain regions following oral administration in lipid-based and lipid-free vehicles. All formulations resulted in a short brain T_max (1 h) and brain-plasma ratios ≥ 3.5, with retention up to 18 h post administration. The highest CBD delivery was observed in the olfactory bulb and striatum, and the medulla pons and cerebellum the lowest. The lipid-free vehicle led to the highest levels of CBD in the whole brain. However, when each anatomical region was assessed individually, the long chain triglyceride-rich rapeseed oil formulation commonly showed optimal performance. The medium chain triglyceride-rich coconut oil formulation did not result in the highest CBD concentration in any brain region. Overall, differences in CBD delivery to the whole brain and various brain regions were observed following administration in different formulations, indicating that the oral formulation selection may be important for optimal delivery to specific regions of the brain.

Functional brain networks underlying the interaction between central and peripheral processes involved in Chinese handwriting in children and adults

The neural mechanisms that support handwriting, an important mode of human communication, are thought to be controlled by a central process (responsible for spelling) and a peripheral process (responsible for motor output). However, the relationship between central and peripheral processes has been debated. Using functional magnetic resonance imaging, this study examined the neural mechanisms underlying this relationship in Chinese handwriting in 36 children (mean age = 10.40 years) and 56 adults (mean age = 22.36 years) by manipulating character frequency (a central variable). Brain network analysis showed that character frequency reconfigured functional brain networks known to underlie motor processes, including the somatomotor and cerebellar network, in both children and adults, indicating that central processing cascades into peripheral processing. Furthermore, the network analysis characterized the interaction profiles between motor networks and linguistic-cognitive networks, fully mapping the neural architecture that supports the interaction of central and peripheral processes involved in handwriting. Taken together, these results reveal the neural interface underlying the interaction between central and peripheral processes involved in handwriting in a logographic writing system, advancing our understanding of the neural basis of handwriting.

Neural Information Processing and Computations of Two-Input Synapses

Information processing in artificial neural networks is largely dependent on the nature of neuron models. While commonly used models are designed for linear integration of synaptic inputs, accumulating experimental evidence suggests that biological neurons are capable of nonlinear computations for many converging synaptic inputs via homo- and heterosynaptic mechanisms. This nonlinear neuronal computation may play an important role in complex information processing at the neural circuit level. Here we characterize the dynamics and coding properties of neuron models on synaptic transmissions delivered from two hidden states. The neuronal information processing is influenced by the cooperative and competitive interactions among synapses and the coherence of the hidden states. Furthermore, we demonstrate that neuronal information processing under two-input synaptic transmission can be mapped to linearly nonseparable XOR as well as basic AND/OR operations. In particular, the mixtures of linear and nonlinear neuron models outperform the fashion-MNIST test compared to the neural networks consisting of only one type. This study provides a computational framework for assessing information processing of neuron and synapse models that may be beneficial for the design of brain-inspired artificial intelligence algorithms and neuromorphic systems.

Neural Algorithms and Circuits for Motor Planning

The brain plans and executes volitional movements. The underlying patterns of neural population activity have been explored in the context of movements of the eyes, limbs, tongue, and head in nonhuman primates and rodents. How do networks of neurons produce the slow neural dynamics that prepare specific movements and the fast dynamics that ultimately initiate these movements? Recent work exploits rapid and calibrated perturbations of neural activity to test specific dynamical systems models that are capable of producing the observed neural activity. These joint experimental and computational studies show that cortical dynamics during motor planning reflect fixed points of neural activity (attractors). Subcortical control signals reshape and move attractors over multiple timescales, causing commitment to specific actions and rapid transitions to movement execution. Experiments in rodents are beginning to reveal how these algorithms are implemented at the level of brain-wide neural circuits.

Relationship Between MR Spectroscopy-Detected Glutamatergic Neurometabolites and Changes in Social Behaviors in a Pilot Open-Label Trial of Memantine for Adults With Autism Spectrum Disorder

BACKGROUND

The neurobiology underlying ASD is largely unknown but altered neural excitability/inhibitory ratios have been reported. Memantine is an N-methyl-D-aspartate (NMDA) glutamatergic antagonist studied for the treatment of core ASD symptoms, with mixed results. We examined whether glutamatergic levels were associated with and predicted response to memantine in an exploratory pilot study.

METHODS

Ten adult participants with ASD underwent proton magnetic resonance spectroscopy (¹H-MRS) imaging at baseline and behavioral assessments before and after 12-weeks of open-label memantine. Post-treatment scores on Clinical Global Impressions-Improvement (CGI-I) for social interaction were the primary outcome measure, and scores on the Social Responsiveness Scale (SRS) were included as a secondary outcome. LCModel was used to quantify the concentrations of Point RESolved Spectroscopy-detected glutamate+glutamine (Glx) (and other neurometabolites, i.e., N-acetylaspartate, NAA; creatine+phosphocreatine, Cr+PCr, and myo-inositol, Ins), within the left dorsolateral prefrontal cortex (LDLPFC) and right (R) posterolateral cerebellum. SPM was used to perform brain tissue segmentation within the spectroscopic voxels. CGI-I scores post-treatment were used to classify the participants into two groups, responders (scores 1-3; n = 5) and non-responders (scores 4-7, or withdrew due to increase behaviors; n = 5). Independent samples t-tests, partial correlations and linear hierarchical regression models (SPSS) were used to determine between-group differences in neurometabolite concentrations and associations between neurometabolites and behavioral scores.

RESULTS

Responders and non-responders did not significantly differ in Glx levels in any region of interest, but differed in NAA levels in LDLPFC (higher in responders vs. non-responders). Although changes in CGI-I social scores were not correlated with Glx in any region of interest, the linear hierarchical regression did reveal that Glx and Ins levels in LDLPFC were predictors of post-treatment CGI-I social scores. Changes in SRS scores were correlated with baseline Cr+PCr levels in the LDLPFC.

DISCUSSION

Our pilot data suggest that baseline Glx, a marker of glutamatergic neurotransmission, did not directly predict response to memantine for social outcomes in adults with ASD. However, interactions between Glx and the neurometabolite associated with glial integrity (Ins) may help predict treatment response. Further, those with highest baseline NAA, a putative neuronal marker, and Cr+pCr, a brain energy metabolism marker, were the best responders. These preliminary results may explain some of the mixed results reported in previous memantine trials in ASD. Future studies will need to examine these results in a larger sample.

Influence of various temporal recoding on pavlovian eyeblink conditioning in the cerebellum

We consider the Pavlovian eyeblink conditioning (EBC) via repeated presentation of paired conditioned stimulus (tone) and unconditioned stimulus (US; airpuff). In an effective cerebellar ring network, we change the connection probability p c from Golgi to granule (GR) cells, and make a dynamical classification of various firing patterns of the GR cells. Individual GR cells are thus found to show various well- and ill-matched firing patterns relative to the US timing signal. Then, these variously-recoded signals are fed into the Purkinje cells (PCs) through the parallel-fibers (PFs). Based on such unique dynamical classification of various firing patterns, we make intensive investigations on the influence of various temporal recoding (i.e., firing patterns) of the GR cells on the synaptic plasticity of the PF-PC synapses and the subsequent learning process for the EBC. We first note that the variously-recoded PF signals are effectively depressed by the (error-teaching) instructor climbing-fiber (CF) signals from the inferior olive neuron. In the case of well-matched PF signals, they are strongly depressed through strong long-term depression (LTD) by the instructor CF signals due to good association between the in-phase PF and the instructor CF signals. On the other hand, practically no LTD occurs for the ill-matched PF signals because most of them have no association with the instructor CF signals. This kind of "effective" depression at the PF-PC synapses coordinates firings of PCs effectively, which then makes effective inhibitory coordination on the cerebellar nucleus neuron [which elicits conditioned response (CR; eyeblink)]. When the learning trial passes a threshold, acquisition of CR begins. In this case, the timing degree T d of CR becomes good due to presence of the ill-matched firing group which plays a role of protection barrier for the timing. With further increase in the number of trials, strength S of CR (corresponding to the amplitude of eyelid closure) increases due to strong LTD in the well-matched firing group, while its timing degree T d decreases. In this way, the well- and the ill-matched firing groups play their own roles for the strength and the timing of CR, respectively. Thus, with increasing the number of learning trials, the (overall) learning efficiency degree L e (taking into consideration both timing and strength of CR) for the CR is increased, and eventually it becomes saturated. Finally, we also discuss dependence of the variety degree for firing patterns of the GR cells and the saturated learning efficiency degree L e of the CR on p c and their relations.

A cerebellar internal model calibrates a feedback controller involved in sensorimotor control

Animals must adapt their behavior to survive in a changing environment. Behavioral adaptations can be evoked by two mechanisms: feedback control and internal-model-based control. Feedback controllers can maintain the sensory state of the animal at a desired level under different environmental conditions. In contrast, internal models learn the relationship between the motor output and its sensory consequences and can be used to recalibrate behaviors. Here, we present multiple unpredictable perturbations in visual feedback to larval zebrafish performing the optomotor response and show that they react to these perturbations through a feedback control mechanism. In contrast, if a perturbation is long-lasting, fish adapt their behavior by updating a cerebellum-dependent internal model. We use modelling and functional imaging to show that the neuronal requirements for these mechanisms are met in the larval zebrafish brain. Our results illustrate the role of the cerebellum in encoding internal models and how these can calibrate neuronal circuits involved in reactive behaviors depending on the interactions between animal and environment.

Diverse inhibitory projections from the cerebellar interposed nucleus

The cerebellum consists of parallel circuit modules that contribute to diverse behaviors, spanning motor to cognitive. Recent work employing cell-type-specific tracing has identified circumscribed output channels of the cerebellar nuclei (CbN) that could confer tight functional specificity. These studies have largely focused on excitatory projections of the CbN, however, leaving open the question of whether inhibitory neurons also constitute multiple output modules. We mapped output and input patterns to intersectionally restricted cell types of the interposed and adjacent interstitial nuclei in mice. In contrast to the widespread assumption of primarily excitatory outputs and restricted inferior olive-targeting inhibitory output, we found that inhibitory neurons from this region ramified widely within the brainstem, targeting both motor- and sensory-related nuclei, distinct from excitatory output targets. Despite differences in output targeting, monosynaptic rabies tracing revealed largely shared afferents to both cell classes. We discuss the potential novel functional roles for inhibitory outputs in the context of cerebellar theory.

Disruption of human brain connectivity networks in patients with cervical spondylotic myelopathy

Background

Brain functional plasticity and reorganization in patients with cervical spondylotic myelopathy (CSM) is increasingly being explored and validated. However, specific topological alterations in functional networks and their role in CSM brain functional reorganization remain unclear. This study investigates the topological architecture of intrinsic brain functional networks in CSM patients using graph theory.

Methods

Functional MRI was conducted on 67 CSM patients and 60 healthy controls (HCs). The topological organization of the whole-brain functional network was then calculated using theoretical graph analysis. The difference in categorical variables between groups was compared using a chi-squared test, while that between continuous variables was evaluated using a two-sample t-test. Nonparametric permutation tests were used to compare network measures between the two groups.

Results

Small-world architecture in functional brain networks were identified in both CSM patients and HCs. Compared with HCs, CSM patients showed a decreased area under the curve (AUC) of the characteristic path length (FDR q=0.040), clustering coefficient (FDR q=0.037), and normalized characteristic path length (FDR q=0.038) of the network. In contrast, there was an increased AUC of normalized clustering coefficient (FDR q=0.014), small-worldness (FDR q=0.009), and global network efficiency (FDR q=0.027) of the network. In local brain regions, nodal topological properties revealed group differences which were predominantly in the default-mode network (DMN), left postcentral gyrus, bilateral putamen, lingual gyrus, and posterior cingulate gyrus.

Conclusions

This study reported altered functional topological organization in CSM patients. Decreased nodal centralities in the visual cortex and sensory-motor regions may indicate sensory-motor dysfunction and blurred vision. Furthermore, increased nodal centralities in the cerebellum may be compensatory for sensory-motor dysfunction in CSM, while the increased DMN may indicate increased psychological processing in CSM patients.

The role of cerebellum in the child neuropsychological functioning

This chapter proposes a review of neuropsychologic and behavior findings in pediatric pathologies of the cerebellum, including cerebellar malformations, pediatric ataxias, cerebellar tumors, and other acquired cerebellar injuries during childhood. The chapter also contains reviews of the cerebellar mutism/posterior fossa syndrome, reported cognitive associations with the development of the cerebellum in typically developing children and subjects born preterm, and the role of the cerebellum in neurodevelopmental disorders such as autism spectrum disorders and developmental dyslexia. Cognitive findings in pediatric cerebellar disorders are considered in the context of known cerebellocerebral connections, internal cellular organization of the cerebellum, the idea of a universal cerebellar transform and computational internal models, and the role of the cerebellum in specific cognitive and motor functions, such as working memory, language, timing, or control of eye movements. The chapter closes with a discussion of the strengths and weaknesses of the cognitive affective syndrome as it has been described in children and some conclusions and perspectives.

Monosynaptic inputs to specific cell types of the intermediate and deep layers of the superior colliculus

The intermediate and deep layers of the midbrain superior colliculus (SC) are a key locus for several critical functions, including spatial attention, multisensory integration, and behavioral responses. While the SC is known to integrate input from a variety of brain regions, progress in understanding how these inputs contribute to SC-dependent functions has been hindered by the paucity of data on innervation patterns to specific types of SC neurons. Here, we use G-deleted rabies virus-mediated monosynaptic tracing to identify inputs to excitatory and inhibitory neurons of the intermediate and deep SC. We observed stronger and more numerous projections to excitatory than inhibitory SC neurons. However, a subpopulation of excitatory neurons thought to mediate behavioral output received weaker inputs, from far fewer brain regions, than the overall population of excitatory neurons. Additionally, extrinsic inputs tended to target rostral excitatory and inhibitory SC neurons more strongly than their caudal counterparts, and commissural SC neurons tended to project to similar rostrocaudal positions in the other SC. Our findings support the view that active intrinsic processes are critical to SC-dependent functions, and will enable the examination of how specific inputs contribute to these functions.

Task-Dependent Recruitment of Modality-Specific and Multimodal Regions during Conceptual Processing

Conceptual knowledge is central to cognitive abilities such as word comprehension. Previous neuroimaging evidence indicates that concepts are at least partly composed of perceptual and motor features that are represented in the same modality-specific brain regions involved in actual perception and action. However, it is unclear to what extent the retrieval of perceptual-motor features and the resulting engagement of modality-specific regions depend on the concurrent task. To address this issue, we measured brain activity in 40 young and healthy participants using functional magnetic resonance imaging, while they performed three different tasks-lexical decision, sound judgment, and action judgment-on words that independently varied in their association with sounds and actions. We found neural activation for sound and action features of concepts selectively when they were task-relevant in brain regions also activated during auditory and motor tasks, respectively, as well as in higher-level, multimodal regions which were recruited during both sound and action feature retrieval. For the first time, we show that not only modality-specific perceptual-motor areas but also multimodal regions are engaged in conceptual processing in a flexible, task-dependent fashion, responding selectively to task-relevant conceptual features.

Prediction signals in the cerebellum: beyond supervised motor learning

While classical views of cerebellar learning have suggested that this structure predominantly operates according to an error-based supervised learning rule to refine movements, emerging evidence suggests that the cerebellum may also harness a wider range of learning rules to contribute to a variety of behaviors, including cognitive processes. Together, such evidence points to a broad role for cerebellar circuits in generating and testing predictions about movement, reward, and other non-motor operations. However, this expanded view of cerebellar processing also raises many new questions about how such apparent diversity of function arises from a structure with striking homogeneity. Hence, this review will highlight both current evidence for predictive cerebellar circuit function that extends beyond the classical view of error-driven supervised learning, as well as open questions that must be addressed to unify our understanding cerebellar circuit function.

Cerebellar Activation During Reading Tasks: Exploring the Dichotomy Between Motor vs. Language Functions in Adults of Varying Reading Proficiency

The nature and extent to which the cerebellum contributes to language processing is not clear. By using fMRI to examine differences in activation intensity in areas associated with motor and language processes, we advance our understanding of how this subcortical structure contributes to language and, more specifically, reading. Functional magnetic resonance imaging data was collected from two groups of adults. One group was classified as typical (proficient) readers, and the other as atypical (less proficient) readers. fMRI was used to measure cerebellar activation during silent reading and silent rapid naming tasks, which differed in degree of language and motor/articulatory processing. Regions of interest associated with motor and language processing were examined in order to compare how cerebellar activation in typical and atypical readers differed as a function of task both within and between groups. Significant differences in activation intensity were noted between individuals of typical and atypical reading proficiency in cerebellar regions associated with motor, but not language processing, during a silent word-reading condition. Additionally, readers who were less proficient showed no differences in activation between tasks in each of the regions of interest within the cerebellum. We provide evidence that, in typical readers, the cerebellum is functionally specialized for reading tasks that vary in language and articulatory processes. In accordance with prior research, we demonstrate that less-proficient adult readers show decreased functional specialization within the cerebellum during reading tasks. We also show that regions of the cerebellum associated with motor/articulatory processing are different between typical and atypically reading adults. Finally, to our knowledge, this is the first brain-imaging study to specifically examine cerebellar activation during rapid naming tasks and we discuss the implications for these findings with regard to current theoretical models that emphasize the link between reading and speech production.

Neocortex-Cerebellum Circuits for Cognitive Processing

Although classically thought of as a motor circuit, the cerebellum is now understood to contribute to a wide variety of cognitive functions through its dense interconnections with the neocortex, the center of brain cognition. Recent investigations have shed light on the nature of cerebellar cognitive processing and information exchange with the neocortex. We review findings that demonstrate widespread reward-related cognitive input to the cerebellum, as well as new studies that have characterized the codependence of processing in the neocortex and cerebellum. Together, these data support a view of the neocortex-cerebellum circuit as a joint dynamic system both in classical sensorimotor contexts and reward-related, cognitive processing. These studies have also expanded classical theory on the computations performed by the cerebellar circuit.

Cerebellar contribution to locomotor behavior: A neurodevelopmental perspective

The developmental trajectory of the formation of cerebellar circuitry has significant implications for locomotor plasticity and adaptive learning at later stages. While there is a wealth of knowledge on the development of locomotor behavior in human infants, children, and adolescents, pre-clinical animal models have fallen behind on the study of the emergence of behavioral motifs in locomotor function across postnatal development. Since cerebellar development is protracted, it is subject to higher risk of genetic or environmental disruption, potentially leading to abnormal behavioral development. This highlights the need for more sophisticated and specific functional analyses of adaptive cerebellar behavior within the context of whole-body locomotion across the entire span of postnatal development. Here we review evidence on cerebellar contribution to adaptive locomotor behavior, highlighting methodologies employed to quantify and categorize behavior at different developmental stages, with the ultimate goal of following the course of early behavioral alterations in neurodevelopmental disorders. Since experimental paradigms used to study cerebellar behavior are lacking in both specificity and applicability to locomotor contexts, we highlight the use of the Erasmus Ladder - an advanced, computerized, fully automated system to quantify adaptive cerebellar learning in conjunction with locomotor function. Finally, we emphasize the need to develop objective, quantitative, behavioral tasks which can track changes in developmental trajectories rather than endpoint measurement at the adult stage of behavior.

Cerebellar contribution to auditory feedback control of speech production: Evidence from patients with spinocerebellar ataxia

The cerebellum has been implicated in the feedforward control of speech production. However, the role of the cerebellum in the feedback control of speech production remains unclear. To address this question, the present event-related potential study examined the behavioral and neural correlates of auditory feedback control of vocal production in patients with spinocerebellar ataxia (SCA) and healthy controls. All participants were instructed to produce sustained vowels while hearing their voice unexpectedly pitch-shifted -200 or -500 cents. The behavioral results revealed significantly larger vocal compensations for pitch perturbations in patients with SCA relative to healthy controls. At the cortical level, patients with SCA exhibited significantly smaller cortical P2 responses that were source localized in the right superior temporal gyrus, primary auditory cortex, and supramarginal gyrus than healthy controls. These findings indicate that reduced brain activity in the right temporal and parietal regions are significant neural contributors to abnormal auditory-motor processing of vocal pitch regulation as a consequence of cerebellar degeneration, which may be related to disrupted reciprocal interactions between the cerebellum and cortical regions that support the top-down modulation of auditory-vocal integration. These differences in behavior and cortical activity between healthy controls and patients with SCA demonstrate that the cerebellum is not only essential for feedforward control but also plays a crucial role in the feedback-based control of speech production.

Cerebellar Control of Reach Kinematics for Endpoint Precision

The cerebellum is well appreciated to impart speed, smoothness, and precision to skilled movements such as reaching. How these functions are executed by the final output stage of the cerebellum, the cerebellar nuclei, remains unknown. Here, we identify a causal relationship between cerebellar output and mouse reach kinematics and show how that relationship is leveraged endogenously to enhance reach precision. Activity in the anterior interposed nucleus (IntA) was remarkably well aligned to reach endpoint, scaling with the magnitude of limb deceleration. Closed-loop optogenetic modulation of IntA activity, triggered on reach, supported a causal role for this activity in controlling reach velocity in real time. Relating endogenous neural variability to kinematic variability, we found that IntA endpoint activity is adaptively engaged relative to variations in initial reach velocity, supporting endpoint precision. Taken together, these results provide a framework for understanding the physiology and pathophysiology of the intermediate cerebellum during precise skilled movements.

Corollary Discharge Signals in the Cerebellum

The cerebellum is known to make movements fast, smooth, and accurate. Many hypotheses emphasize the role of the cerebellum in computing learned predictions important for sensorimotor calibration and feedforward control of movements. Hypotheses of the computations performed by the cerebellum in service of motor control borrow heavily from control systems theory, with models that frequently invoke copies of motor commands, called corollary discharge. This review describes evidence for corollary discharge inputs to the cerebellum and highlights the hypothesized roles for this information in cerebellar motor-related computations. Insights into the role of corollary discharge in motor control, described here, are intended to inform the exciting but still untested roles of corollary discharge in cognition, perception, and thought control relevant in psychiatric disorders.

Cooperation of the vestibular and cerebellar networks in anxiety disorders and depression

The discipline of affective neuroscience is concerned with the neural bases of emotion and mood. The past decades have witnessed an explosion of research in affective neuroscience, increasing our knowledge of the brain areas involved in fear and anxiety. Besides the brain areas that are classically associated with emotional reactivity, accumulating evidence indicates that both the vestibular and cerebellar systems are involved not only in motor coordination but also influence both cognition and emotional regulation in humans and animal models. The cerebellar and the vestibular systems show the reciprocal connection with a myriad of anxiety and fear brain areas. Perception anticipation and action are also major centers of interest in cognitive neurosciences. The cerebellum is crucial for the development of an internal model of action and the vestibular system is relevant for perception, gravity-related balance, navigation and motor decision-making. Furthermore, there are close relationships between these two systems. With regard to the cooperation between the vestibular and cerebellar systems for the elaboration and the coordination of emotional cognitive and visceral responses, we propose that altering the function of one of the systems could provoke internal model disturbances and, as a result, anxiety disorders followed potentially with depressive states.

A cortico-cerebellar loop for motor planning

Persistent and ramping neural activity in the frontal cortex anticipates specific movements1-6. Preparatory activity is distributed across several brain regions7,8, but it is unclear which brain areas are involved and how this activity is mediated by multi-regional interactions. The cerebellum is thought to be primarily involved in the short-timescale control of movement9-12; however, roles for this structure in cognitive processes have also been proposed13-16. In humans, cerebellar damage can cause defects in planning and working memory13. Here we show that persistent representation of information in the frontal cortex during motor planning is dependent on the cerebellum. Mice performed a sensory discrimination task in which they used short-term memory to plan a future directional movement. A transient perturbation in the medial deep cerebellar nucleus (fastigial nucleus) disrupted subsequent correct responses without hampering movement execution. Preparatory activity was observed in both the frontal cortex and the cerebellar nuclei, seconds before the onset of movement. The silencing of frontal cortex activity abolished preparatory activity in the cerebellar nuclei, and fastigial activity was necessary to maintain cortical preparatory activity. Fastigial output selectively targeted the behaviourally relevant part of the frontal cortex through the thalamus, thus closing a cortico-cerebellar loop. Our results support the view that persistent neural dynamics during motor planning is maintained by neural circuits that span multiple brain regions17, and that cerebellar computations extend beyond online motor control13-15,18.

Coordinated cerebellar climbing fiber activity signals learned sensorimotor predictions

The prevailing model of cerebellar learning states that climbing fibers (CFs) are both driven by, and serve to correct, erroneous motor output. However, this model is grounded largely in studies of behaviors that utilize hardwired neural pathways to link sensory input to motor output. To test whether this model applies to more flexible learning regimes that require arbitrary sensorimotor associations, we developed a cerebellar-dependent motor learning task that is compatible with both mesoscale and single-dendrite-resolution calcium imaging in mice. We found that CFs were preferentially driven by and more time-locked to correctly executed movements and other task parameters that predict reward outcome, exhibiting widespread correlated activity in parasagittal processing zones that was governed by these predictions. Together, our data suggest that such CF activity patterns are well-suited to drive learning by providing predictive instructional input that is consistent with an unsigned reinforcement learning signal but does not rely exclusively on motor errors.

Eye movement desensitization and reprocessing as a treatment for PTSD: current neurobiological theories and a new hypothesis

Eye movement desensitization and reprocessing (EMDR), a form of psychotherapy for individuals with post-traumatic stress disorder (PTSD), has long been a controversial topic, hampered in part by a lack of understanding of the neural mechanisms that contribute to its remedial effect. Here, we review current theories describing EMDR's potential neurobiological mechanisms of action involving working memory, interhemispheric communication, de-arousal, and memory reconsolidation. We then discuss recent studies describing the temporal and spatial aspects of smooth pursuit and predictive saccades, which resemble those made during EMDR, and their neural correlates within the default mode network (DMN) and cerebellum. We hypothesize that if the production of bilateral predictive eye movements is supportive of DMN and cerebellum activation, then therapies that shift the brain towards this state correspondingly would benefit the processes regulated by these structures (i.e., memory retrieval, relaxation, and associative learning), all of which are essential components for PTSD recovery. We propose that the timing of sensory stimulation may be relevant to treatment effect and could be adapted across different patients depending on their baseline saccade metrics. Empirical data in support of this model are reviewed and experimental predictions are discussed.

Optogenetic fMRI and electrophysiological identification of region-specific connectivity between the cerebellar cortex and forebrain

Complex animal behavior is produced by dynamic interactions between discrete regions of the brain. As such, defining functional connections between brain regions is critical in gaining a full understanding of how the brain generates behavior. Evidence suggests that discrete regions of the cerebellar cortex functionally project to the forebrain, mediating long-range communication potentially important in motor and non-motor behaviors. However, the connectivity map remains largely incomplete owing to the challenge of driving both reliable and selective output from the cerebellar cortex, as well as the need for methods to detect region specific activation across the entire forebrain. Here we utilize a paired optogenetic and fMRI (ofMRI) approach to elucidate the downstream forebrain regions modulated by activating a region of the cerebellum that induces stereotypical, ipsilateral forelimb movements. We demonstrate with ofMRI, that activating this forelimb motor region of the cerebellar cortex results in functional activation of a variety of forebrain and midbrain areas of the brain, including the hippocampus and primary motor, retrosplenial and anterior cingulate cortices. We further validate these findings using optogenetic stimulation paired with multi-electrode array recordings and post-hoc staining for molecular markers of activated neurons (i.e. c-Fos). Together, these findings demonstrate that a single discrete region of the cerebellar cortex is capable of influencing motor output and the activity of a number of downstream forebrain as well as midbrain regions thought to be involved in different aspects of behavior.

Inferior olive CRF plays a role in motor performance under challenging conditions

A well-coordinated stress response is pivotal for an organisms' survival. Corticotropin-releasing factor (CRF) is an essential component of the emotional and neuroendocrine stress response, however its role in cerebellar functions is poorly understood. Here, we explore the role of CRF in the inferior olive (IO) nucleus, which is a major source of input to the cerebellum. Using a CRF reporter line, in situ hybridization and immunohistochemistry, we demonstrate very high levels of the CRF neuropeptide expression throughout the IO sub-regions. By generating and characterizing IO-specific CRF knockdown and partial IO-CRF knockout, we demonstrate that reduction in IO-CRF levels is sufficient to induce motor deficiency under challenging conditions, irrespective of basal locomotion or anxiety-like behavior. Furthermore, we show that chronic social defeat stress induces a persistent decrease in IO-CRF levels, and that IO-CRF mRNA is upregulated shortly following stressful situations that demand a complex motor response. Taken together our results indicate a role for IO-CRF in challenge-induced motor responses.

Time, touch and temperature affect perceived finger position and ownership in the grasp illusion

KEY POINTS

The brain's internal model of the body and the sense of body ownership are fundamental to interaction with the world. It is thought that temporally congruent, repetitive multisensory stimuli are required to elicit a sense of body ownership. Here we investigate the ability of static cutaneous stimuli - passively grasping an artificial finger - to induce body ownership and alter perceived body position; we also investigate how physical characteristics of grasped objects alter these senses. We show that static cutaneous stimuli can alter perceived body position and induce an illusion of ownership and also that signals of temperature, texture and shape of grasped finger-sized objects influence body ownership. Thus, these aspects of human proprioception can be altered by a single sustained sensory stimulus and by the physical characteristics of held objects.

ABSTRACT

Perceived body position and ownership are fundamental to our ability to sense and interact with the world. Previous work indicates that temporally congruent, repetitive multisensory stimuli are needed to alter the sense of body ownership. In the present study 30 subjects passively grasped an artificial rubber finger with their left index and thumb while their right index finger, located 12 cm below, was lightly clamped. Fingers with varied physical characteristics were also passively grasped to determine how these characteristics influenced perceived body position and ownership. Subjects immediately felt their hands to be 5.3 cm [3.4-7.3] (mean [95%CI]) closer, a feeling that remained after 3 min (6.0 cm [4.5-7.5]). By the end of the trial, perceived ownership increased by 1.2 [0.6-1.9] points on a 7-point Likert scale, with the group average moving from 'neither agree or disagree' at the start to 'somewhat agree' at the end. Compared to grasping a control rubber finger, grasping a cold, rough, oddly shaped or rectangular shaped finger-like object reduced perceived ownership. These results provide new insights into the role of cutaneous sensory receptors in defining these aspects of proprioception, and the speed with which these effects occur. Static touch rapidly induces large, sustained changes in perceived body position and prolonged exposure to these cutaneous inputs, alone, can induce a sense of body ownership. Also, certain physical characteristics of grasped objects influence the sense of body ownership.

The impact of cerebellar transcranial direct current stimulation (tDCS) on learning fine-motor sequences

The cerebellum has been shown to be important for skill learning, including the learning of motor sequences. We investigated whether cerebellar transcranial direct current stimulation (tDCS) would enhance learning of fine motor sequences. Because the ability to generalize or transfer to novel task variations or circumstances is a crucial goal of real world training, we also examined the effect of tDCS on performance of novel sequences after training. In Study 1, participants received either anodal, cathodal or sham stimulation while simultaneously practising three eight-element key press sequences in a non-repeating, interleaved order. Immediately after sequence practice with concurrent tDCS, a transfer session was given in which participants practised three interleaved novel sequences. No stimulation was given during transfer. An inhibitory effect of cathodal tDCS was found during practice, such that the rate of learning was slowed in comparison to the anodal and sham groups. In Study 2, participants received anodal or sham stimulation and a 24 h delay was added between the practice and transfer sessions to reduce mental fatigue. Although this consolidation period benefitted subsequent transfer for both tDCS groups, anodal tDCS enhanced transfer performance. Together, these studies demonstrate polarity-specific effects on fine motor sequence learning and generalization.This article is part of the themed issue 'New frontiers for statistical learning in the cognitive sciences'.

Neonatal eyelid conditioning during sleep

Using an eyelid conditioning paradigm modeled after that developed by Little, Lipsitt, and Rovee-Collier (1984), Fifer et al. (2010) demonstrated that newborn infants learn during sleep. This study examined the role of sleep state in neonatal learning. We recorded electroencephalogram (EEG), respiratory, and cardiovascular activity from sleeping full term newborn infants during delay eyelid conditioning. In the experimental group (n = 21), a tone was paired with an air puff to the eye. Consistent with Fifer et al. (2010), newborn infants reliably learned during sleep. The experimental group more than doubled EMR rates to a tone alone, while a control group (n = 17) presented with unpaired tones and puffs maintained low EMR rates. Infant learners were more likely to produce a conditioned EMR during quiet sleep compared to active sleep. Understanding the influence of sleep state on conditioned responses will inform the potential use of eyelid conditioning for early screening.

Transcranial Alternating Current Stimulation (tACS) Mechanisms and Protocols

Perception, cognition and consciousness can be modulated as a function of oscillating neural activity, while ongoing neuronal dynamics are influenced by synaptic activity and membrane potential. Consequently, transcranial alternating current stimulation (tACS) may be used for neurological intervention. The advantageous features of tACS include the biphasic and sinusoidal tACS currents, the ability to entrain large neuronal populations, and subtle control over somatic effects. Through neuromodulation of phasic, neural activity, tACS is a powerful tool to investigate the neural correlates of cognition. The rapid development in this area requires clarity about best practices. Here we briefly introduce tACS and review the most compelling findings in the literature to provide a starting point for using tACS. We suggest that tACS protocols be based on functional brain mechanisms and appropriate control experiments, including active sham and condition blinding.

Motor Imagery-Based Rehabilitation: Potential Neural Correlates and Clinical Application for Functional Recovery of Motor Deficits after Stroke

Motor imagery (MI), defined as the mental implementation of an action in the absence of movement or muscle activation, is a rehabilitation technique that offers a means to replace or restore lost motor function in stroke patients when used in conjunction with conventional physiotherapy procedures. This article briefly reviews the concepts and neural correlates of MI in order to promote improved understanding, as well as to enhance the clinical utility of MI-based rehabilitation regimens. We specifically highlight the role of the cerebellum and basal ganglia, premotor, supplementary motor, and prefrontal areas, primary motor cortex, and parietal cortex. Additionally, we examine the recent literature related to MI and its potential as a therapeutic technique in both upper and lower limb stroke rehabilitation.

The Contribution of Brainstem and Cerebellar Pathways to Auditory Recognition

The cerebellum has been known to play an important role in motor functions for many years. More recently its role has been expanded to include a range of cognitive and sensory-motor processes, and substantial neuroimaging and clinical evidence now points to cerebellar involvement in most auditory processing tasks. In particular, an increase in the size of the cerebellum over recent human evolution has been attributed in part to the development of speech. Despite this, the auditory cognition literature has largely overlooked afferent auditory connections to the cerebellum that have been implicated in acoustically conditioned reflexes in animals, and could subserve speech and other auditory processing in humans. This review expands our understanding of auditory processing by incorporating cerebellar pathways into the anatomy and functions of the human auditory system. We reason that plasticity in the cerebellar pathways underpins implicit learning of spectrotemporal information necessary for sound and speech recognition. Once learnt, this information automatically recognizes incoming auditory signals and predicts likely subsequent information based on previous experience. Since sound recognition processes involving the brainstem and cerebellum initiate early in auditory processing, learnt information stored in cerebellar memory templates could then support a range of auditory processing functions such as streaming, habituation, the integration of auditory feature information such as pitch, and the recognition of vocal communications.

Machine Learning Capabilities of a Simulated Cerebellum

This paper describes the learning and control capabilities of a biologically constrained bottom-up model of the mammalian cerebellum. Results are presented from six tasks: 1) eyelid conditioning; 2) pendulum balancing; 3) proportional-integral-derivative control; 4) robot balancing; 5) pattern recognition; and 6) MNIST handwritten digit recognition. These tasks span several paradigms of machine learning, including supervised learning, reinforcement learning, control, and pattern recognition. Results over these six domains indicate that the cerebellar simulation is capable of robustly identifying static input patterns even when randomized across the sensory apparatus. This capability allows the simulated cerebellum to perform several different supervised learning and control tasks. On the other hand, both reinforcement learning and temporal pattern recognition prove problematic due to the delayed nature of error signals and the simulator's inability to solve the credit assignment problem. These results are consistent with previous findings which hypothesize that in the human brain, the basal ganglia is responsible for reinforcement learning, while the cerebellum handles supervised learning.

The Errors of Our Ways: Understanding Error Representations in Cerebellar-Dependent Motor Learning

The cerebellum is essential for error-driven motor learning and is strongly implicated in detecting and correcting for motor errors. Therefore, elucidating how motor errors are represented in the cerebellum is essential in understanding cerebellar function, in general, and its role in motor learning, in particular. This review examines how motor errors are encoded in the cerebellar cortex in the context of a forward internal model that generates predictions about the upcoming movement and drives learning and adaptation. In this framework, sensory prediction errors, defined as the discrepancy between the predicted consequences of motor commands and the sensory feedback, are crucial for both on-line movement control and motor learning. While many studies support the dominant view that motor errors are encoded in the complex spike discharge of Purkinje cells, others have failed to relate complex spike activity with errors. Given these limitations, we review recent findings in the monkey showing that complex spike modulation is not necessarily required for motor learning or for simple spike adaptation. Also, new results demonstrate that the simple spike discharge provides continuous error signals that both lead and lag the actual movements in time, suggesting errors are encoded as both an internal prediction of motor commands and the actual sensory feedback. These dual error representations have opposing effects on simple spike discharge, consistent with the signals needed to generate sensory prediction errors used to update a forward internal model.

A comparative approach to cerebellar function: insights from electrosensory systems

Despite its simple and highly-ordered circuitry the function of the cerebellum remains a topic of vigorous debate. This review explores connections between the cerebellum and sensory processing structures that closely resemble the cerebellum in terms of their evolution, development, patterns of gene expression, and circuitry. Recent studies of cerebellum-like structures involved in electrosensory processing in fish have provided insights into the functions of granule cells and unipolar brush cells-cell types shared with the cerebellum. We also discuss the possibility, supported by recent studies, that generating and subtracting predictions of the sensory consequences of motor commands may be core functions shared by both cerebellum-like structures and the cerebellum.

Neural Mechanisms for Predicting the Sensory Consequences of Behavior: Insights from Electrosensory Systems

Perception of the environment requires differentiating between external sensory inputs and those that are self-generated. Some of the clearest insights into the neural mechanisms underlying this process have come from studies of the electrosensory systems of fish. Neurons at the first stage of electrosensory processing generate negative images of the electrosensory consequences of the animal's own behavior. By canceling out the effects of predictable, self-generated inputs, negative images allow for the selective encoding of unpredictable, externally generated stimuli. Combined experimental and theoretical studies of electrosensory systems have led to detailed accounts of how negative images are formed at the level of synaptic plasticity rules, cells, and circuits. Here, I review these accounts and discuss their implications for understanding how predictions of the sensory consequences of behavior may be generated in other sensory structures and the cerebellum.

Cued Reactivation of Motor Learning during Sleep Leads to Overnight Changes in Functional Brain Activity and Connectivity

Sleep plays a role in memory consolidation. This is demonstrated by improved performance and neural plasticity underlying that improvement after sleep. Targeted memory reactivation (TMR) allows the manipulation of sleep-dependent consolidation through intentionally biasing the replay of specific memories in sleep, but the underlying neural basis of these altered memories remains unclear. We use functional magnetic resonance imaging (fMRI) to show a change in the neural representation of a motor memory after targeted reactivation in slow-wave sleep (SWS). Participants learned two serial reaction time task (SRTT) sequences associated with different auditory tones (high or low pitch). During subsequent SWS, one sequence was reactivated by replaying the associated tones. Participants were retested on both sequences the following day during fMRI. As predicted, they showed faster reaction times for the cued sequence after targeted memory reactivation. Furthermore, increased activity in bilateral caudate nucleus and hippocampus for the cued relative to uncued sequence was associated with time in SWS, while increased cerebellar and cortical motor activity was related to time in rapid eye movement (REM) sleep. Functional connectivity between the caudate nucleus and hippocampus was also increased after targeted memory reactivation. These findings suggest that the offline performance gains associated with memory reactivation are supported by altered functional activity in key cognitive and motor networks, and that this consolidation is differentially mediated by both REM sleep and SWS.

Slow-wave sleep and rapid eye movement sleep are associated with the reactivation and consolidation of a motor skill within distinct brain networks.

After a motor skill is learned, the memory undergoes "offline" processing so that improvement occurs even without further practice. Sleep has been shown to enhance this consolidation and, in the process, to reorganize the brain regions involved. However, it remains unclear how sleep does this, and whether different sleep stages have different contributions. One popular idea is that the memory trace is reactivated during slow-wave sleep—a period of sleep characterized by synchronized activity at a slow frequency and high amplitude, as recorded by electroencephalography (EEG)—which drives memory reorganization within the brain. To test this in humans, we took advantage of "targeted memory reactivation," where replay of specific memories is cued by presentation of a sound that was present during learning. After sleep, motor performance was faster for cued memories, suggesting that the trace was consolidated during sleep. Coupled with this, brain activation and connectivity in several motor-learning areas was enhanced for the cued memory. Furthermore, some changes in brain activity were associated with time spent in slow-wave sleep, while others were associated with time spent in rapid-eye movement sleep. These observations provide further insight into sleep's unique role in memory consolidation by showing that offline skill enhancement depends on the reactivation of specific memories, and the associated changes in neural activity may rely upon processing that unfolds across different stages of sleep.

Sensorimotor dysfunctions as primary features of autism spectrum disorders

Motor impairments in autism spectrum disorders (ASD) have received far less research attention than core social-communication and cognitive features. Yet, behavioral, neurophysiological, neuroimaging and histopathological studies have documented abnormal motor system development in the majority of individuals with ASD suggesting that these deficits may be primary to the disorder. There are several unique advantages to studying motor development in ASD. First, the neurophysiological substrates of motor skills have been well-characterized via animal and human lesion studies. Second, many of the single- gene disorders associated with ASD also are characterized by motor dysfunctions. Third, recent evidence suggests that the onset of motor dysfunctions may precede the emergence of social and communication deficits during the first year of life in ASD. Motor deficits documented in ASD indicate disruptions throughout the neuroaxis affecting cortex, striatum, the cerebellum and brainstem. Questions remain regarding the timing and development of motor system alterations in ASD, their association with defining clinical features, and their potential for parsing heterogeneity in ASD. Pursuing these questions through neurobiologically informed translational research holds great promise for identifying gene-brain pathways associated with ASD.

Trace Eyeblink Conditioning in Mice Is Dependent upon the Dorsal Medial Prefrontal Cortex, Cerebellum, and Amygdala: Behavioral Characterization and Functional Circuitry

Trace eyeblink conditioning is useful for studying the interaction of multiple brain areas in learning and memory. The goal of the current work was to determine whether trace eyeblink conditioning could be established in a mouse model in the absence of elicited startle responses and the brain circuitry that supports this learning. We show here that mice can acquire trace conditioned responses (tCRs) devoid of startle while head-restrained and permitted to freely run on a wheel. Most mice (75%) could learn with a trace interval of 250 ms. Because tCRs were not contaminated with startle-associated components, we were able to document the development and timing of tCRs in mice, as well as their long-term retention (at 7 and 14 d) and flexible expression (extinction and reacquisition). To identify the circuitry involved, we made restricted lesions of the medial prefrontal cortex (mPFC) and found that learning was prevented. Furthermore, inactivation of the cerebellum with muscimol completely abolished tCRs, demonstrating that learned responses were driven by the cerebellum. Finally, inactivation of the mPFC and amygdala in trained animals nearly abolished tCRs. Anatomical data from these critical regions showed that mPFC and amygdala both project to the rostral basilar pons and overlap with eyelid-associated pontocerebellar neurons. The data provide the first report of trace eyeblink conditioning in mice in which tCRs were driven by the cerebellum and required a localized region of mPFC for acquisition. The data further reveal a specific role for the amygdala as providing a conditioned stimulus-associated input to the cerebellum.

Longitudinal FDG microPET imaging of neuropathic pain: does cerebellar activity correlate with neuropathic pain development in a rat model?

BACKGROUND

We used [F-18] FDG microPET imaging as part of a longitudinal study to investigate changes in the brain.

METHODS

Glucose metabolism during the development of neuropathic pain after tibial and sural nerve transection (TST) model rats. MicroPET images were obtained 1 week before operation and then weekly for 8 weeks post-operation.

RESULTS

The behavioral test was performed immediately after the every FDG administration. After TST modeling, neuropathic pain rats showed increased mechanical sensitivity of the injured hind paw. The withdrawal response to mechanical pain stimulation by von Frey filaments was observed within the first week (3.8 ± 0.73), and it rapidly increased in the third week (7.13 ± 0.82). This response reached a peak in the fourth week after surgery (9.0 ± 0.53), which persisted until the eighth week. In microPET scan imaging, cerebellum, which initially started from the ansiform lobule, was activated gradually to all part from the third week in all image acquisitions through the eighth week.

CONCLUSIONS

The longitudinal microPET scan study of brains from neuropathic pain rat models showed sequential cerebellar activity that was in accordance with results from behavioral test responses, thus supporting a role for the cerebellum in the development of neuropathic pain.

Cerebellar Premotor Output Neurons Collateralize to Innervate the Cerebellar Cortex

Motor commands computed by the cerebellum are hypothesized to use corollary discharge, or copies of outgoing commands, to accelerate motor corrections. Identifying sources of corollary discharge, therefore, is critical for testing this hypothesis. Here we verified that the pathway from the cerebellar nuclei to the cerebellar cortex in mice includes collaterals of cerebellar premotor output neurons, mapped this collateral pathway, and identified its postsynaptic targets. Following bidirectional tracer injections into a distal target of the cerebellar nuclei, the ventrolateral thalamus, we observed retrogradely labeled somata in the cerebellar nuclei and mossy fiber terminals in the cerebellar granule layer, consistent with collateral branching. Corroborating these observations, bidirectional tracer injections into the cerebellar cortex retrogradely labeled somata in the cerebellar nuclei and boutons in the ventrolateral thalamus. To test whether nuclear output neurons projecting to the red nucleus also collateralize to the cerebellar cortex, we used a Cre-dependent viral approach, avoiding potential confounds of direct red nucleus-to-cerebellum projections. Injections of a Cre-dependent GFP-expressing virus into Ntsr1-Cre mice, which express Cre selectively in the cerebellar nuclei, retrogradely labeled somata in the interposed nucleus, and putative collateral branches terminating as mossy fibers in the cerebellar cortex. Postsynaptic targets of all labeled mossy fiber terminals were identified using immunohistochemical Golgi cell markers and electron microscopic profiles of granule cells, indicating that the collaterals of nuclear output neurons contact both Golgi and granule cells. These results clarify the organization of a subset of nucleocortical projections that constitute an experimentally accessible corollary discharge pathway within the cerebellum.