The cerebellum as sensory acquisition controller: Commentary on “the underestimated cerebellum” by Leiner et al

Functional brain networks underlying perceptual switching: auditory streaming and verbal transformations

Recent studies have shown that auditory scene analysis involves distributed neural sites below, in, and beyond the auditory cortex (AC). However, it remains unclear what role each site plays and how they interact in the formation and selection of auditory percepts. We addressed this issue through perceptual multistability phenomena, namely, spontaneous perceptual switching in auditory streaming (AS) for a sequence of repeated triplet tones, and perceptual changes for a repeated word, known as verbal transformations (VTs). An event-related fMRI analysis revealed brain activity timelocked to perceptual switching in the cerebellum for AS, in frontal areas for VT, and the AC and thalamus for both. The results suggest that motor-based prediction, produced by neural networks outside the auditory system, plays essential roles in the segmentation of acoustic sequences both in AS and VT. The frequency of perceptual switching was determined by a balance between the activation of two sites, which are proposed to be involved in exploring novel perceptual organization and stabilizing current perceptual organization. The effect of the gene polymorphism of catechol-O-methyltransferase (COMT) on individual variations in switching frequency suggests that the balance of exploration and stabilization is modulated by catecholamines such as dopamine and noradrenalin. These mechanisms would support the noteworthy flexibility of auditory scene analysis.

Functional implications of tactile projection patterns to the lateral hemispheres of the cerebellum of the albino rat: the legacy of Wally Welker

In the late 1970s, Wally Welker and his colleagues published a series of papers describing the first high-resolution physiological maps of tactile mossy fiber projections to the granule cell layer of the rat. Over the subsequent decade, his laboratory continued to explore the implications of these results for cerebellar connectivity and function while also extending the basic mapping results to a number of additional mammalian species. In each case, the maps revealed several surprising features, including a dominance of tactile (cutaneous inputs), robust short latency responses from the sensory periphery, and a fractured patchy somatotopic organization of receptive fields. This paper summarizes the major results of these micromapping experiments and reconsiders their implications for cerebellar function in light of more recent experimental data. The paper also explores the relationship between these fundamental discoveries and Wally Welker's theory-neutral approach to experimental science.

The cerebellum, cerebellar disorders, and cerebellar research--two centuries of discoveries

Research on the cerebellum is evolving rapidly. The exquisiteness of the cerebellar circuitry with a unique geometric arrangement has fascinated researchers from numerous disciplines. The painstaking works of pioneers of these last two centuries, such as Rolando, Flourens, Luciani, Babinski, Holmes, Cajal, Larsell, or Eccles, still exert a strong influence in the way we approach cerebellar functions. Advances in genetic studies, detailed molecular and cellular analyses, profusion of brain imaging techniques, emergence of behavioral assessments, and reshaping of models of cerebellar function are generating an immense amount of knowledge. Simultaneously, a better definition of cerebellar disorders encountered in the clinic is emerging. The essentials of a trans-disciplinary blending are expanding. The analysis of the literature published these last two decades indicates that the gaps between domains of research are vanishing. The launch of the society for research on the cerebellum (SRC) illustrates how cerebellar research is burgeoning. This special issue gathers the contributions of the inaugural conference of the SRC dedicated to the mechanisms of cerebellar function. Contributions were brought together around five themes: (1) cerebellar development, death, and regeneration; (2) cerebellar circuitry: processing and function; (3) mechanisms of cerebellar plasticity and learning; (4) cerebellar function: timing, prediction, and/or coordination?; (5) anatomical and disease perspectives on cerebellar function.

The effect of early musical training on adult motor performance: evidence for a sensitive period in motor learning

Developmental changes in the human brain coincide with and underlie changes in a wide range of motor and cognitive abilities. Neuroimaging studies have shown that musical training can result in structural and functional plasticity in the brains of musicians, and that this plasticity is greater for those who begin training early in life. However, previous studies have not controlled for differences between early-trained (ET) and late-trained (LT) musicians in the total number of years of musical training and experience. In the present experiment, we tested musicians who began training before and after the age of 7 on learning of a timed motor sequence task. The groups were matched for years of musical experience, years of formal training and hours of current practice. Results showed that ET musicians performed better than LT musicians, and that this performance advantage persisted after 5 days of practice. Performance differences were greatest for a measure of response synchronization, suggesting that early training has its greatest effect on neural systems involved in sensorimotor integration and timing. These findings support the idea that there may be a sensitive period in childhood where enriched motor training through musical practice results in long-lasting benefits for performance later in life. These results are also consistent with the results of studies showing structural changes in motor-related regions of the brain in musicians that are specifically related to training early in life.

When the brain plays music: auditory-motor interactions in music perception and production

Music performance is both a natural human activity, present in all societies, and one of the most complex and demanding cognitive challenges that the human mind can undertake. Unlike most other sensory-motor activities, music performance requires precise timing of several hierarchically organized actions, as well as precise control over pitch interval production, implemented through diverse effectors according to the instrument involved. We review the cognitive neuroscience literature of both motor and auditory domains, highlighting the value of studying interactions between these systems in a musical context, and propose some ideas concerning the role of the premotor cortex in integration of higher order features of music with appropriately timed and organized actions.

fMRI investigation of cortical and subcortical networks in the learning of abstract and effector-specific representations of motor sequences

A visuo-motor sequence can be learned as a series of visuo-spatial cues or as a sequence of effector movements. Earlier imaging studies have revealed that a network of brain areas is activated in the course of motor sequence learning. However, these studies do not address the question of the type of representation being established at various stages of visuo-motor sequence learning. In an earlier behavioral study, we demonstrated that acquisition of visuo-spatial sequence representation enables rapid learning in the early stage and progressive establishment of somato-motor representation helps speedier execution by the late stage. We conducted functional magnetic resonance imaging (fMRI) experiments wherein subjects learned and practiced the same sequence alternately in normal and rotated settings. In one rotated setting (visual), subjects learned a new motor sequence in response to an identical sequence of visual cues as in normal. In another rotated setting (motor), the display sequence was altered as compared to normal, but the same sequence of effector movements was used to perform the sequence. Comparison of different rotated settings revealed analogous transitions both in the cortical and subcortical sites during visuo-motor sequence learning-a transition of activity from parietal to parietal-premotor and then to premotor cortex and a concomitant shift was observed from anterior putamen to a combined activity in both anterior and posterior putamen and finally to posterior putamen. These results suggest a putative role for engagement of different cortical and subcortical networks at various stages of learning in supporting distinct sequence representations.

fMRI investigation of cortical and subcortical networks in the learning of abstract and effector-specific representations of motor sequences

A visuo-motor sequence can be learned as a series of visuo-spatial cues or as a sequence of effector movements. Earlier imaging studies have revealed that a network of brain areas is activated in the course of motor sequence learning. However, these studies do not address the question of the type of representation being established at various stages of visuo-motor sequence learning. In an earlier behavioral study, we demonstrated that acquisition of visuo-spatial sequence representation enables rapid learning in the early stage and progressive establishment of somato-motor representation helps speedier execution by the late stage. We conducted functional magnetic resonance imaging (fMRI) experiments wherein subjects learned and practiced the same sequence alternately in normal and rotated settings. In one rotated setting (visual), subjects learned a new motor sequence in response to an identical sequence of visual cues as in normal. In another rotated setting (motor), the display sequence was altered as compared to normal, but the same sequence of effector movements was used to perform the sequence. Comparison of different rotated settings revealed analogous transitions both in the cortical and subcortical sites during visuo-motor sequence learning-a transition of activity from parietal to parietal-premotor and then to premotor cortex and a concomitant shift was observed from anterior putamen to a combined activity in both anterior and posterior putamen and finally to posterior putamen. These results suggest a putative role for engagement of different cortical and subcortical networks at various stages of learning in supporting distinct sequence representations.

The cerebellar-hypothalamic circuits: potential pathways underlying cerebellar involvement in somatic-visceral integration

The cerebellum has been considered only as a classical subcortical center for motor control. However, accumulating experimental and clinical evidences have revealed that the cerebellum also plays an important role in cognition, for instance, in learning and memory, as well as in emotional behavior and in nonsomatic activities, such as visceral and immunological responses. Although it is not yet clear through which pathways such cerebellar nonsomatic functions are mediated, the direct bidirectional connections between the cerebellum and the hypothalamus, a high autonomic center, have recently been demonstrated in a series of neuroanatomical investigations on a variety of mammals and indicated to be potential pathways underlying the cerebellar autonomic modulation. The direct hypothalamocerebellar projections originate from the widespread hypothalamic nuclei/areas and terminate in both the cerebellar cortex as multilayered fibers and the cerebellar nuclei. Immunohistochemistry studies have offered fairly convincing evidence that some of these projecting fibers are histaminergic. It has been suggested that through their excitatory effects on cerebellar cortical and nuclear cells mediated by metabotropic histamine H(2) and/or H(1) receptors, the hypothalamocerebellar histaminergic fibers participate in cerebellar modulation of somatic motor as well as non-motor responses. On the other hand, the direct cerebellohypothalamic projections arise from all cerebellar nuclei (fastigial, anterior and posterior interpositus, and dentate nuclei) and reach almost all hypothalamic nuclei/areas. Neurophysiological and neuroimaging studies have demonstrated that these connections may be involved in feeding, cardiovascular, osmotic, respiratory, micturition, immune, emotion, and other nonsomatic regulation. These observations provide support for the hypothesis that the cerebellum is an essential modulator and coordinator for integrating motor, visceral and behavioral responses, and that such somatic-visceral integration through the cerebellar circuitry may be fulfilled by means of the cerebellar-hypothalamic circuits.

Cerebellum and M1 interaction during early learning of timed motor sequences

We used positron emission tomography (PET) to examine within-day learning of timed motor sequences. The results of this experiment are novel in showing an interaction between cerebellum and primary motor cortex (M1) during learning that appears to be mediated by the dentate nucleus (DN) and in demonstrating that activity in these regions is directly related to performance. Subjects were scanned during learning (LRN) across three blocks of practice and during isochronous (ISO) and perceptual (PER) baseline conditions. CBF was compared across blocks of learning and between the LRN and baseline conditions. Results demonstrated an interaction between the cerebellum and M1 such that earlier, poorer performance was associated with greater activity in the cerebellar hemispheres and later, better performance was associated with greater activity in M1. Inter-regional correlation analyses confirmed that as CBF in the cerebellum decreases, blood flow in M1 increases. Importantly, these analyses also revealed that activity in cerebellar cortex was positively correlated with activity in right DN and that DN activity was negatively correlated with blood flow in M1. Activity in the cerebellar hemispheres early in learning is likely related to error correction mechanisms which optimize movement kinematics resulting in improved performance. Concurrent DN activity may be related to encoding of this information and DN output to M1 may play a role in consolidation processes that lay down motor memories. Increased activity in M1 later in learning may reflect strengthening of synaptic connections associated with changes in motor maps that are characteristic of learning in both animals and humans.

Cerebellar contributions to motor timing: a PET study of auditory and visual rhythm reproduction

The perception and production of temporal patterns, or rhythms, is important for both music and speech. However, the way in which the human brain achieves accurate timing of perceptual input and motor output is as yet little understood. Central control of both motor timing and perceptual timing across modalities has been linked to both the cerebellum and the basal ganglia (BG). The present study was designed to test the hypothesized central control of temporal processing and to examine the roles of the cerebellum, BG, and sensory association areas. In this positron emission tomography (PET) activation paradigm, subjects reproduced rhythms of increasing temporal complexity that were presented separately in the auditory and visual modalities. The results provide support for a supramodal contribution of the lateral cerebellar cortex and cerebellar vermis to the production of a timed motor response, particularly when it is complex and/or novel. The results also give partial support to the involvement of BG structures in motor timing, although this may be more directly related to implementation of the motor response than to timing per se. Finally, sensory association areas and the ventrolateral frontal cortex were found to be involved in modality-specific encoding and retrieval of the temporal stimuli. Taken together, these results point to the participation of a number of neural structures in the production of a timed motor response from an external stimulus. The role of the cerebellum in timing is conceptualized not as a clock or counter but simply as the structure that provides the necessary circuitry for the sensory system to extract temporal information and for the motor system to learn to produce a precisely timed response.

Sensory and cognitive functions

New neuroimaging studies provide striking evidence that the cerebellum is intensely and selectively active during sensory and cognitive tasks, even in the absence of explicit or implicit motor behavior. Focal activity is observed in the lateral cerebellar hemispheres during the processing of auditory, visual, cutaneous, spatial, and tactile information, and in anterior-medial cerebellar regions during somatomotor behavior. Moreover, a double dissociation exists between (a) cerebellar activity and sensory processing and (b) motor behavior and activity in known motor areas in the cerebral cortex. These findings contradict the classical motor coordination theory of cerebellar function but are predicted by, or are at least consistent with, new alternative theories.

Skill learning

This chapter reviews recent experiments that have examined the functional neuroanatomy of motor and visuomotor skill learning using brain imaging techniques such as single photon emission computed tomography, positron emission tomography, and functional magnetic resonance imaging. Special attention has been given to the cerebral blood flow changes in the cerebellum that are associated with the acquisition of these skills, although localizations of other activated regions (cortical and subcortical) are also included. The cognitive processes involved in different skill acquisition paradigms are discussed with particular reference to the learning stages at which subjects were scanned. This approach examines the conditions that are likely to produce cerebellar activation and helps us understand the role of the cerebellum in acquiring skilled behaviors.

Control of sensory data acquisition

This chapter describes a new theory of cerebellar function which posits that the cerebellum is specifically involved in monitoring and adjusting the acquisition of most of the sensory data on which the rest of the nervous system depends. If correct, the cerebellum is not itself responsible for any particular behaviorally related function, whether "motor," "sensory," or "cognitive." Instead the cerebellum facilitates the efficiency with which other brain structures perform their own functions. In this way the cerebellum is seen as being useful but not necessary for many different kinds of brain functions. This chapter describes how this theory of cerebellar function has arisen from detailed study of the pattern of tactile afferent projections to the rat cerebellum as well as from an analysis of the neural circuitry that processes that information. It is proposed that the breadth of cerebellar involvement is reflected in the growing number of tasks which induce cerebellar activity, including cognitive tasks, even though the cerebellum is not itself directly involved in those tasks.

Lateral cerebellar hemispheres actively support sensory acquisition and discrimination rather than motor control

This study examined a new hypothesis proposing that the lateral cerebellum is not activated by motor control per se, as widely assumed, but is engaged during the acquisition and discrimination of tactile sensory information. This proposal derives from neurobiological studies of these regions of the rat cerebellum. Magnetic resonance imaging of the lateral cerebellar output nucleus (dentate) of humans during passive and active sensory tasks confirmed four a priori implications of this hypothesis. Dentate nuclei responded to cutaneous stimuli, even when there were no accompanying overt finger movements. Finger movements not associated with tactile sensory discrimination produced no dentate activation. Sensory discrimination with the fingers induced an increase in dentate activation, with or without finger movements. Finally, dentate activity was greatest when there was the most opportunity to modulate the acquisition of the sensory tactile data: when the discrimination involved the active repositioning of tactile sensory surface of the fingers. Furthermore, activity in cerebellar cortex was strongly correlated with observed dentate activity. This distinct four-way pattern of effects strongly challenges other cerebellar theories. However, contrary to appearances, neither our hypothesis nor findings conflict with behavioral effects of cerebellar damage, neurophysiological data on animals performing motor tasks, or cerebellar contribution to nonmotor, perceptual, and cognitive tasks.