Separate cerebellar areas for motor control

Extended source analysis of movement related potentials (MRPs) for self-paced hand and foot movements demonstrates opposing cerebral and cerebellar laterality: a preliminary study

The cerebellum is known to have extensive reciprocal connectivity with the cerebral cortex, including with prefrontal and posterior parietal cortex, which play an important role on the planning and execution of voluntary movement. In the present article we report an exploratory non-invasive electrophysiological study of the activity of the cerebellum and cerebrum during voluntary finger and foot movements. In a sample of five healthy adult subjects, we recorded EEG and the electro-cerebellogram (ECeG) with a 10% cerebellar extension montage during voluntary left and right index finger and foot movements. EMG was recorded from finger extensors and flexors and from the tibialis anterior and soleus muscles and was used to generate triggers for movement related averaging (-2000 to +2000 ms). Source analysis was conducted over five epochs defined relative to EMG onset: whole epoch (-1000 to +1000 ms), pre-move 1000 (-1000 to 0 ms), pre-move 500 (-500 to 0 ms), post-move 500 (0 to +500 ms) and post-move 1000 (0 to +1000 ms). This yielded a total of 123 cerebral and 65 cerebellar dipole clusters from across all epochs, including the pre-movement epochs, which were then subject to statistical analysis. These demonstrated predominantly contralateral dominance for the cerebral clusters, but predominantly ipsilateral dominance for the cerebellar clusters. In addition, both cerebral and cerebellar clusters showed evidence of a somatotopic gradient, medially (X-axis) for the cerebral clusters, and medially and dorso-ventrally (Z-axis) for the cerebellar clusters. These findings support the value of recording cerebellar ECeG and demonstrate its potential to contribute to understanding cerebellar function.

Activation of Cerebellum, Basal Ganglia and Thalamus During Observation and Execution of Mouth, hand, and foot Actions

Humans and monkey studies showed that specific sectors of cerebellum and basal ganglia activate not only during execution but also during observation of hand actions. However, it is unknown whether, and how, these structures are engaged during the observation of actions performed by effectors different from the hand. To address this issue, in the present fMRI study, healthy human participants were required to execute or to observe grasping acts performed with different effectors, namely mouth, hand, and foot. As control, participants executed and observed simple movements performed with the same effectors. The results show that: (1) execution of goal-directed actions elicited somatotopically organized activations not only in the cerebral cortex but also in the cerebellum, basal ganglia, and thalamus; (2) action observation evoked cortical, cerebellar and subcortical activations, lacking a clear somatotopic organization; (3) in the territories displaying shared activations between execution and observation, a rough somatotopy could be revealed in both cortical, cerebellar and subcortical structures. The present study confirms previous findings that action observation, beyond the cerebral cortex, also activates specific sectors of cerebellum and subcortical structures and it shows, for the first time, that these latter are engaged not only during hand actions observation but also during the observation of mouth and foot actions. We suggest that each of the activated structures processes specific aspects of the observed action, such as performing internal simulation (cerebellum) or recruiting/inhibiting the overt execution of the observed action (basal ganglia and sensory-motor thalamus).

Neural substrates underlying motor skill learning in chronic hemiparetic stroke patients

Motor skill learning is critical in post-stroke motor recovery, but little is known about its underlying neural substrates. Recently, using a new visuomotor skill learning paradigm involving a speed/accuracy trade-off in healthy individuals we identified three subpopulations based on their behavioral trajectories: fitters (in whom improvement in speed or accuracy coincided with deterioration in the other parameter), shifters (in whom speed and/or accuracy improved without degradation of the other parameter), and non-learners. We aimed to identify the neural substrates underlying the first stages of motor skill learning in chronic hemiparetic stroke patients and to determine whether specific neural substrates were recruited in shifters versus fitters. During functional magnetic resonance imaging (fMRI), 23 patients learned the visuomotor skill with their paretic upper limb. In the whole-group analysis, correlation between activation and motor skill learning was restricted to the dorsal prefrontal cortex of the damaged hemisphere (DLPFC_damh: r = −0.82) and the dorsal premotor cortex (PMd_damh: r = 0.70); the correlations was much lesser (−0.16 < r > 0.25) in the other regions of interest. In a subgroup analysis, significant activation was restricted to bilateral posterior parietal cortices of the fitters and did not correlate with motor skill learning. Conversely, in shifters significant activation occurred in the primary sensorimotor cortex_damh and supplementary motor area_damh and in bilateral PMd where activation changes correlated significantly with motor skill learning (r = 0.91). Finally, resting-state activity acquired before learning showed a higher functional connectivity in the salience network of shifters compared with fitters (qFDR < 0.05). These data suggest a neuroplastic compensatory reorganization of brain activity underlying the first stages of motor skill learning with the paretic upper limb in chronic hemiparetic stroke patients, with a key role of bilateral PMd.

Grasping with the Press of a Button: Grasp-selective Responses in the Human Anterior Intraparietal Sulcus Depend on Nonarbitrary Causal Relationships between Hand Movements and End-effector Actions

Evidence implicates ventral parieto-premotor cortices in representing the goal of grasping independent of the movements or effectors involved [Umilta, M. A., Escola, L., Intskirveli, I., Grammont, F., Rochat, M., Caruana, F., et al. When pliers become fingers in the monkey motor system. Proceedings of the National Academy of Sciences, U.S.A., 105, 2209-2213, 2008; Tunik, E., Frey, S. H., & Grafton, S. T. Virtual lesions of the anterior intraparietal area disrupt goal-dependent on-line adjustments of grasp. Nature Neuroscience, 8, 505-511, 2005]. Modern technologies that enable arbitrary causal relationships between hand movements and tool actions provide a strong test of this hypothesis. We capitalized on this unique opportunity by recording activity with fMRI during tasks in which healthy adults performed goal-directed reach and grasp actions manually or by depressing buttons to initiate these same behaviors in a remotely located robotic arm (arbitrary causal relationship). As shown previously [Binkofski, F., Dohle, C., Posse, S., Stephan, K. M., Hefter, H., Seitz, R. J., et al. Human anterior intraparietal area subserves prehension: A combined lesion and functional MRI activation study. Neurology, 50, 1253-1259, 1998], we detected greater activity in the vicinity of the anterior intraparietal sulcus (aIPS) during manual grasp versus reach. In contrast to prior studies involving tools controlled by nonarbitrarily related hand movements [Gallivan, J. P., McLean, D. A., Valyear, K. F., & Culham, J. C. Decoding the neural mechanisms of human tool use. Elife, 2, e00425, 2013; Jacobs, S., Danielmeier, C., & Frey, S. H. Human anterior intraparietal and ventral premotor cortices support representations of grasping with the hand or a novel tool. Journal of Cognitive Neuroscience, 22, 2594-2608, 2010], however, responses within the aIPS and premotor cortex exhibited no evidence of selectivity for grasp when participants employed the robot. Instead, these regions showed comparable increases in activity during both the reach and grasp conditions. Despite equivalent sensorimotor demands, the right cerebellar hemisphere displayed greater activity when participants initiated the robot's actions versus when they pressed a button known to be nonfunctional and watched the very same actions undertaken autonomously. This supports the hypothesis that the cerebellum predicts the forthcoming sensory consequences of volitional actions [Blakemore, S. J., Frith, C. D., & Wolpert, D. M. The cerebellum is involved in predicting the sensory consequences of action. NeuroReport, 12, 1879-1884, 2001]. We conclude that grasp-selective responses in the human aIPS and premotor cortex depend on the existence of nonarbitrary causal relationships between hand movements and end-effector actions.

Functional asymmetry in the cerebellum: a brief review

Recent discoveries on the way in which the cerebellum carries out higher non-motor functions, have stimulated a proliferation of researches into functional integration and neural mechanisms in the cerebellum. Cerebellar functional asymmetry is a special characteristic of cerebellar functional organization and the cerebro-cerebellar circuitry that underlies task performance. Multi-level neuroimaging studies demonstrate that cerebellar functional asymmetry has a rather complex pattern, and may be correlated with practice or certain disorders. In this review, we summarize some new and important advances in the understanding of functional laterality of the cerebellum in primary motor and higher cognitive functions, and highlight the differences in the patterns of cerebellar functional asymmetry in the various functional domains. We propose that cerebellar functional asymmetry may be associated with the pattern of connectivity between a large number of widely distributed brain areas and between special cerebellar functional regions. It is suggested that cerebro-cerebellar circuits in particular play an important role in cerebellar functional asymmetry. Finally, we propose that multi-scale connectivity analyses and careful studies of high-level cerebellar functional asymmetry would make an important contribution to the understanding of the human cerebellum and cerebral neural networks.

Juggling with the brain - thought and action in the human motor system

Empirical findings from various research fields indicate that cognitive and motor processes are far less dissimilar than previously thought. The present chapter takes a neuroscientific perspective and offers evidence for similarities between cognition and action focusing on three key players of the classical motor system: the primary motor cortex, the cerebellum, and the premotor cortex. Briefly, although movement execution is apparently supported in part by the same cerebral resources engaged in cognitive processes, the three brain regions reviewed here are differentially engaged in more or less action-bound cognitive processes.

Dissociation of the neural networks recruited during a haptic object-recognition task: complementary results with a tensorial independent component analysis

BACKGROUND AND PURPOSE

The cerebral and cerebellar networks involved in bimanual object recognition were assessed by blood oxygen level-dependent functional MR imaging by using multivariate model-free analysis, because conventional univariate model-based analysis, such as the general linear model (GLM), does not allow investigation of resting, background, and transiently task-related brain activities.

MATERIALS AND METHODS

Data from 14 healthy right-handed volunteers, scanned while successively performing bilateral finger movements and a bimanual tactile-tactile matching discrimination task were analyzed by using tensor-independent component analysis (TICA), which computes statistically independent spatiotemporal processes (P > .7) thought to reflect specific and distinct anatomofunctional neural networks. These results were compared with the network obtained in a previous study by using the same paradigm based on GLM to evaluate the advantages of TICA.

RESULTS

TICA characterized and distinguished the following: 1) resting-state networks such as the default-mode networks, 2) networks transiently synchronized with the beginning and end of the task, such as temporo-pericentral and temporo-pericentral-occipital networks, and 3) task-related networks such as cerebello-fronto-parietal, cerebello-prefrontocingulo-insular, and cerebello-parietal networks.

CONCLUSION

Bimanual tactile-tactile matching discrimination specifically recruits a complex neural network, which can be dissociated into 3 distinct but cooperative neural subnetworks related to sensorimotor function, salience detection, executive control, and, possibly, sensory expectation. This tripartite network involved in bimanual object recognition could not be demonstrated by GLM. Moreover, TICA allowed monitoring of the temporal succession of the networks recruited during the resting phase, audition of the "go" and "stop" signals, and the tactile discrimination task.

Neural correlates of simple unimanual discrete and continuous movements: a functional imaging study at 3 T

INTRODUCTION

The cerebral and cerebellar network involved in unimanual continuous and discrete movements was studied in blood oxygenation level-dependent functional magnetic resonance imaging (fMRI) at 3 T.

METHODS

Seven healthy right-handed volunteers were scanned (1) while drawing a circle with the tip of the right index finger (continuous motor task), and (2) while drawing a triangle with the tip of the right index finger (discrete motor task).

RESULTS

In both motor tasks, extensive activations were observed in the sensorimotor (M1/S1), parietal, prefrontal, insular, lateral occipital (LOC) and anterior cerebellar cortices. Subcortical activations within red, thalamic and lentiform nuclei were also detected. However, discrete movements were specifically followed by the recruitment of the left orbitofrontal cortex, right dentate nucleus and the second cerebellar homunculus (HVIII), and bilateral and stronger activation of the sensorimotor cortical areas, whereas continuous movements specifically activated the right prefrontal cortex and the lateral hemispherical part of the neocerebellum (crus 1).

CONCLUSION

We confirm the findings of previous studies showing partly distinct neural networks involved in monitoring continuous and discrete movements, but we found new differential neural relays within the prefrontal, insular and neocerebellar cortices.

fMRI changes in relapsing-remitting multiple sclerosis patients complaining of fatigue after IFNbeta-1a injection

If fatigue in multiple sclerosis (MS) is related to an abnormal activation of the sensorimotor brain network, the activity of such a network should vary with varying fatigue. We studied 22 patients treated with interferon beta 1a (IFNbeta-1a; Avonex, Biogen, Cambridge, MA) with no fatigue (10) and with reversible fatigue (12). fMRI examinations were performed: 1) the same day of IFNbeta-1a injection (no fatigue; entry), 2) the day after IFNbeta-1a injection (fatigue; time 1), and 3) 4 days after IFNbeta-1a injection (no fatigue; time 2). Patients performed a simple motor task with the right, clinically unaffected hand. At time 1, compared with entry and time 2, MS patients with reversible fatigue showed an increased activation of the thalamus bilaterally. In MS patients without fatigue thalamus was more activated at entry than at time 1. In both groups at entry the primary SMC and the SMA were more activated than at times 1 and 2. At entry and time 1, when compared to patients with reversible fatigue, those without showed increased activations of the SII. Conversely, patients with reversible fatigue had increased activations of the thalamus and of several regions of the frontal lobes. An abnormal recruitment of the fronto-thalamic circuitry is associated with IFNbeta-1a-induced fatigue in MS patients.

Influence of body segment position during in-phase and antiphase hand and foot movements: a kinematic and functional MRI study

Behavioral studies have provided important insights into the mechanisms governing interlimb coordination. In this study, we combined kinematic and functional magnetic resonance imaging (fMRI) analysis to investigate the brain cortical and subcortical areas involved in interlimb coordination and the influence of direction of movement and of body segment position on the activity of those areas. Fifteen right-handed healthy subjects were studied while performing cyclic in-phase and antiphase hand and foot movements with the dominant, right limbs, with the upper limb positioned either prone or supine, and in front or behind with respect to the trunk. When contrasting antiphase to in-phase movements, fMRI analysis demonstrated an increased recruitment of a widespread sensorimotor network (including regions in the frontal and parietal lobes, bilaterally, the cingulated motor area, the thalami, the visual cortex, and the cerebellum) considered to function in motor, sensory, and multimodal integration processing. When contrasting the anterior to the posterior position of the upper limb with respect to the trunk, we found different recruitment patterns in the frontal and parietal regions as well as the preferential recruitment of the basal ganglia, the insula, and the cerebellum during the first condition and of regions located in the temporal lobes during the second one. Different brain areas are engaged at a different extent during interlimb coordination. In addition to the relative difficulty of the movement, the different cognitive and sensorial loads needed to control and perform the motor act might be responsible for these findings.

Reorganization of Brain Activity for Multiple Internal Models After Short But Intensive Training

Internal models are neural mechanisms that can mimic the input-output properties of controlled objects. Our studies have shown that: 1) an internal model for a novel tool is acquired in the cerebellum (Imamizu et al., 2000); 2) internal models are modularly organized in the cerebellum (Imamizu et al., 2003); 3) their outputs are sent to the premotor regions after learning (Tamada et al., 1999); and 4) the prefrontal and parietal regions contribute to the blending of the outputs (Imamizu et al., 2004). Here, we investigated changes in global neural networks resulting from the acquisition of a new internal model. Human subjects manipulated three types of rotating joystick whose cursor appeared at a position rotated 60 degrees, 110 degrees, or 160 degrees around the screen's center. In a pre-test after long-term training (5 days) for the 60 degrees and 160 degrees joysticks, brain activation was scanned during manipulation of the three joysticks. The subjects were then trained for the 110 degrees for only 25 min. In a post-test, activation was scanned using the same method as the pre-test. Comparisons of the post-test to the pre-test revealed that the volume of activation decreased in most of the regions where activation for the three rotations was observed. However, there was an increase in volume at a marginally significant level (p < .08) only in the inferior-lateral cerebellum and only for the 110 degrees joystick. In the cerebral cortex, activation related to 110 degrees decreased in the prefrontal and parietal regions but increased in the premotor and supplementary motor area (SMA) regions. These results can be explained by a model in which outputs of the 60 degrees and 160 degrees internal models are blended by prefrontal and parietal regions to cope with the novel 110 degrees joystick before the 25-minute training; after the acquisition within the cerebellum of an internal model for the 110 degrees, output is directly sent to the premotor and SMA regions, and activation in these regions increases.

Different memory types for generating saccades at different stages of learning

It has been proposed that positional memories encoded in different types of reference frame are used for the reaching hand movement in different stages of learning. However, the types of reference frame employed for generating behavior at each stage of learning remain unclear, particularly for saccades. To examine the types of reference frame for target positions, we analyzed the saccade of monkeys performing an oculomotor task. The task required the animal to make a learning-based saccade to one of the eight landmark positions specified by the color of a fixation point. According to the color of the fixation point, the target landmark position was fixed in all experimental blocks (FIX trial) or altered to other landmark positions block by block (ALTER trial). Although the monkeys learned the target landmark position in both the FIX and the ALTER trials, once the landmarks became invisible, the success rate remained high only in the FIX trials. These results suggest that the target position was learned on the basis of the landmark positions in the early stage of learning. However, the memory of the target position in space was formed after sufficient training. When the fixation point was shifted horizontally by 5 degrees and the landmarks were invisible, the saccades in the ALTER trials were made to the normal target landmark position whereas those in the FIX trials were made to the point approximately 5 degrees shifted horizontally from the normal target landmark position. These results suggest that the target position in space was initially represented in the head-centered or world-centered reference frame and then in the eye-centered reference frame. Analysis of saccade end-points indicated that a kinematically similar saccade was generated for each FIX trial. These results showed that memories encoded by different reference frames were formed to generate a saccade while the saccade toward the same target was repeatedly executed.

The cerebellum in the cerebro-cerebellar network for the control of eye and hand movements--an fMRI study

The coordination of optical information and manipulation of objects in space by eye and hand movements is controlled by a cerebro-cerebellar network. The differential influence of prefrontal, motor, or parietal areas in combination with cerebellar areas, especially within the posterior hemispheres, on the control of eye and hand movements is not very well defined. Using fMRI we investigated the functional representation of isolated or combined eye and hand movements within the cerebellum and the impact of differential cognitive preload on the activation patterns. Each task consisted of the performance of saccades or hand movements triggered by a cue presented on a screen in front of the scanner. Saccades were tested for visually guided saccades, triple step saccades, and for visuospatial memory. Sequential finger opposition movements were tested for predictive and nonpredictive movements. Combined and isolated eye-hand reaching movements were tested toward a target presented in 5 different horizontal positions. Visually guided saccades activated the cerebellar vermis lobuli VI-VII, triple step saccades, including visuospatial memorization, in addition the cerebellar hemispheres lobuli VII-VIII. Sequential finger movements and reaching movements activated a cerebellar network consisting of the lobuli IV-VI, the vermis, and the lobuli VII-VIII with broader areas and additional regions especially within the lobus VII for more complex movements. The combined in contrast to the isolated performance of eye and hand movements demonstrated specialized activation foci within the cerebellar vermis and posterior hemispheres. We could demonstrate a differential representation of eye and hand movements within the cerebellum. Additional "cognitive" preload within a given task leads to additional activation of the posterior cerebellar hemispheres, with a subspecialization corresponding to premotor and parietal area connections.

The cerebellar second homunculus remains silent during passive bimanual movements

In a previous study, we showed that the second homunculus in lobule VIII of the cerebellum is activated during bilateral out-of-phase index finger-thumb opposition, implying a role in motor coordination. However, several recent studies indicate that the cerebellum could be more actively involved in sensory information processing during movement. Therefore, as lobule VIII activation could involve either a motor or a proprioceptive component, these two components must be distinguished and their relative contribution must be determined. Using functional imaging, we studied cerebellar activation of the same region during passively induced index finger-thumb opposition of both hands in in-phase and out-of-phase modes, thereby excluding the voluntary movement component. No significant activation was detected in lobule VIII. Intense activation of lobule VIII, obtained during active, out-of-phase bimanual movements, therefore does not involve a significant sensory component related to direct proprioceptive feedback. This result is strongly in favour of the specific recruitment of lobule VIII during out-of-phase movements related more to complex motor timing than to sensory function.

Role of the cerebellum in implicit motor skill learning: a PET study

To depict neural substrates of implicit motor learning, regional cerebral blood flow was measured using positron emission tomography (PET) in 13 volunteers in the rest condition and during performance of a unimanual two-ball rotation task. Subjects rotated two balls in a single hand; a slow rotation (0.5 Hz) was followed by two sessions requiring as rapid rotation as possible. The process was repeated four times by a single hand (Block 1) and then by the opposite hand (Block 2). One group of volunteers began with the right hand (n = 7), and the other with the left (n = 6). Performance was assessed by both quickness and efficiency of movements. The former was assessed with the maximum number of rotation per unit time, and the latter with the electromyographic activity under constant speed of the movement. Both showed learning transfer from the right hand to the left hand. Activation of cerebrum and cerebellum varied according to hand. Activation common to both hands occurred in the bilateral dorsal premotor cortex and parasagittal cerebellum, right inferior frontal gyms, left lateral cerebellum and thalamus, supplementary motor area, and cerebellar vermis. The left lateral cerebellum showed the most prominent activation on the first trial of the novel task, and hence may be related the early phase of learning, or "what to do" learning. Left parasagittal cerebellum activity diminished with training both in first and second blocks, correlating inversely with task performance. This region may therefore be involved in later learning or "how to do" learning. The activity of these regions was less prominent with prior training than without it. Thus the left cerebellar hemisphere may be related to learning transfer across hands.

A functional MRI study of cortical activations associated with object manipulation in patients with MS

Previous functional magnetic resonance imaging (fMRI) studies of simple motor tasks have shown that in patients with multiple sclerosis (MS), there is an increased recruitment of several regions part of a complex sensorimotor network. These studies have suggested that this might be the case because patients tend to activate, when performing a simple motor task, regions that are usually activated in healthy subjects during the performance of more complex tasks due to the presence of subcortical structural damage. In this study, we tested this hypothesis by comparing the patterns of cortical activations during the performance of two tasks with different levels of complexity from 16 MS patients and 16 age- and sex-matched controls. The first task (simple) consisted of flexion-extension of the last four fingers of the right hand, and the second task (complex) consisted of object manipulation. During the simple task, MS patients had, when compared to controls, more significant activations of the supplementary motor area (SMA), secondary sensorimotor area, posterior lobe of the cerebellum, superior parietal gyrus (SPG), and inferior frontal gyrus (IFG). These three latter regions are part of a fronto-parietal circuit, whose activation occurs typically in the contralateral hemisphere of healthy subjects during object manipulation, as shown also by the present study. During the performance of the complex task, MS patients showed an increased bilateral recruitment of several areas of the fronto-parietal circuit associated with object manipulation, as well of several other areas, which were mainly in the frontal lobes. This study confirms that some of the regions that are activated by MS patients during the performance of simple motor tasks are part of more complex pathways, recruited by healthy subjects when more complex and difficult tasks have to be performed.

Specific neocerebellar activation during out-of-phase bimanual movements

We used fMRI to study cerebellar activation during index finger-thumb opposition of the right hand and index finger-thumb opposition of both hands in in-phase and out-of-phase modes. The right hand movement activates the contralateral anterior lobe of the cerebellum. During bimanual in-phase movements, this activity pattern becomes bilateral. More interestingly, bilateral out-of-phase movements recruit the cerebellar posterior lobe VIII, which likely corresponds to the second homunculus. As out-of-phase movements differ from the in-phase movements only by their temporal complexity and their attentional awareness, this study demonstrates the preferential involvement of the cerebellar second homunculus in the control of complex movements.

A functional MRI study of movement-associated cortical changes in patients with Devic's neuromyelitis optica

Movement-associated cortical changes have been shown in several neurological conditions and were found to be associated to the extent of brain and cord damage. Devic's neuromyelitis optica (DNO) is characterized by a severe involvement of the cord and optic nerve, with sparing of the brain. To assess the actual role of cord pathology on the pattern of movement-associated cortical recruitment, we obtained functional magnetic resonance imaging (fMRI) from patients with DNO and investigated whether the extent of brain activation is correlated with the extent of cervical cord damage. We studied 10 right-handed DNO patients and 15 sex- and age-matched healthy controls. The MRI assessment consisted of the following: (a) fMRI during repetitive flexion extension of the last four fingers of the right and left hand, (b) brain and cervical cord conventional MRI, and (c) cervical cord magnetization transfer (MT) MRI. Compared to controls and for both tasks, DNO patients had an increased recruitment of several regions of the sensorimotor network (primary sensorimotor cortex, postcentral gyrus, middle frontal gyrus, rolandic operculum, secondary sensorimotor cortex, precuneus, and cerebellum) and of several other regions mainly in the temporal and occipital lobes, such as MT/V5, the fusiform gyrus, the cuneus, and the parahippocampal gyrus. For both tasks, strong correlations (r values ranging from -0.76 to -0.85) were found between relative activations of cortical sensorimotor areas and the severity of cervical cord damage. This study shows an abnormal pattern of movement-associated cortical activations in patients with DNO, which extends beyond the 'classical' sensorimotor network and also involves visual areas devoted to motion processing. The correlation found between fMRI changes and the extent of cord damage suggests that such functional cortical changes might have an adaptive role in limiting the clinical outcome of DNO structural pathology.

Muscle afferent inputs from the hand activate human cerebellum sequentially through parallel and climbing fiber systems

OBJECTIVE

Spatio-temporal response characteristics of the human cerebellum to median nerve stimulation (MNS) were studied with the use of a whole-head magnetoencephalographic (MEG) system covering the cerebellum and upper cervical spine.

METHODS

Neuromagnetic responses from the cerebellum were recorded following electric stimulation of the right median nerve in 12 subjects. In 6 out of 12 subjects, the responses to the left median nerve and to the right index or middle finger stimulation were also recorded.

RESULTS

The medial part of the cerebellum (spinocerebellum) was activated by MNS. In contrast, there were no responses from the cerebellum to the finger stimulation, suggesting that muscle afferent inputs are the source of cerebellar activation for MNS. The cerebellar responses consisted of 3 or 4 components of alternating polarity within 90 ms post-stimulus: the current direction for the first component was from the depth to the surface of the anterior lobe.

CONCLUSIONS

From the timing and current direction, we speculate that the 4 components reflect, respectively, (1) excitatory postsynaptic potentials (EPSPs) of granule cells, (2) Purkinje cell EPSPs at the distal dendrites driven by parallel fibers, (3) Purkinje cell EPSPs at the soma and the proximal dendrites mediated by climbing fibers and (4) second Purkinje cell EPSPs at the distal dendrites driven by parallel fibers.

SIGNIFICANCE

We first visualized serial activation of the human spinocerebellum following MNS noninvasively with MEG.

Modulation of cerebellar activation by predictive and non-predictive sequential finger movements

We investigated the modulation of cerebellar activation by predictive and non-predictive sequential finger movements. It is hypothesized that the prediction of desired movement sequences and adaptation to new movement parameters is mediated by the cerebellum. Using functional MRI at 1.5 T, seven normal subjects performed sequential finger to thumb opposition movements, either in predictive (repeatedly 2,3,4,5) or non-predictive (randomized) fashion at a constant frequency of 1 Hz. Performance and error rates were monitored by simultaneous recording of the finger movements. Predictive sequential finger opposition movements activated a cerebellar network including the lobuli IV-VI ipsilateral to the movements, the contralateral lobuli IV-VI, the vermis, and lobuli VIIB-VIII ipsilaterally. Non-predictive compared to predictive finger opposition movements activated a broader area within the ipsi- and contralateral anterior cerebellum, lobuli IV-VI, the vermis, and the ipsilateral lobuli VIIB-VIII. Additional activation foci were found in the contralateral lobuli VIIA and VIIB-VIII. Our study demonstrates a modulated information processing within the cerebellar network dependent on the predictability of movement sequences.

Learning of sequences of finger movements and timing: frontal lobe and action-oriented representation

Motor sequence learning involves learning of a sequence of effectors with which to execute a series of movements and learning of a sequence of timings at which to execute the movements. In this study, we have segregated the neural correlates of the two learning mechanisms. Moreover, we have found an interaction between the two learning mechanisms in the frontal areas, which we claim as suggesting action-oriented coding in the frontal lobe. We used positron emission tomography and compared three learning conditions with a visuo-motor control condition. In two learning conditions, the subjects learned either a sequence of finger movements with random timing or a sequence of timing with random use of fingers. In the third condition the subjects learned to execute a sequence of specific finger movements at specific timing; we argue that it was only in this condition that the motor sequence was coded as an action-oriented representation. By looking for condition by session interactions (learning vs. control conditions over sessions), we have removed nonspecific time effects and identified areas that showed a learning-related increment of activation during learning. Learning of a finger sequence was associated with an increment of activation in the right intraparietal sulcus region and medial parietal cortex, whereas learning of a timing sequence was associated with an increment of activation in the lateral cerebellum, suggesting separate mechanisms for learning effector and temporal sequences. The left intraparietal sulcus region showed an increment of activation in learning of both finger and timing sequences, suggesting an overlap between the two learning mechanisms. We also found that the mid-dorsolateral prefrontal cortex, together with the medial and lateral premotor areas, became increasingly active when subjects learned a sequence that specified both fingers and timing, that is, when subjects were able to prepare specific motor action. These areas were not active when subjects learned a sequence that specified fingers or timing alone, that is, when subjects were still dependent on external stimuli as to the timing or fingers with which to execute the movements. Frontal areas may integrate the effector and temporal information of a motor sequence and implement an action-oriented representation so as to perform a motor sequence accurately and quickly. We also found that the mid-dorsolateral prefrontal cortex was distinguished from the ventrolateral prefrontal cortex and anterior fronto-polar cortex, which showed sustained activity throughout learning sessions and did not show either an increment or decrement of activation.

Sensorimotor mapping of the human cerebellum: fMRI evidence of somatotopic organization

Functional magnetic resonance imaging (fMRI) was employed to determine areas of activation in the cerebellar cortex in 46 human subjects during a series of motor tasks. To reduce the variance due to differences in individual anatomy, a specific transformational procedure for the cerebellum was introduced. The activation areas for movements of lips, tongue, hands, and feet were determined and found to be sharply confined to lobules and sublobules and their sagittal zones in the rostral and caudal spino-cerebellar cortex. There was a clear symmetry mirroring at the midline. The activation mapped as two distinct homunculoid representations. One, a more extended representation, was located upside down in the superior cerebellum, and a second one, doubled and smaller, in the inferior cerebellum. The two representations were remarkably similar to those proposed by Snider and Eldred [1951] five decades ago. In the upper representation, an intralimb somatotopy for the right elbow, wrist, and fingers was revealed. The maps seem to confirm earlier electrophysiological findings of sagittal zones in animals. They differ, however, from micromapping reports on fractured somatotopic maps in the cerebellar cortex of mammals. We assume that the representations that we observed are not solely the result of spatial integration of hemodynamic events underlying the fMRI method and may reflect integration of afferent peripheral and central information in the cerebellar cortex.

Effects of accuracy constraints on reach-to-grasp movements in cerebellar patients

Reach-to-grasp movements of patients with pathology restricted to the cerebellum were compared with those of normal controls. Two types of paradigms with different accuracy constraints were used to examine whether cerebellar impairment disrupts the stereotypic relationship between arm transport and grip aperture and whether the variability of this relationship is altered when greater accuracy is required. The movements were made to either a vertical dowel or to a cross bar of a small cross. All subjects were asked to reach for either target at a fast but comfortable speed, grasp the object between the index finger and thumb, and lift it a short distance off the table. In terms of the relationship between arm transport and grip aperture, the control subjects showed a high consistency in grip aperture and wrist velocity profiles from trial to trial for movements to both the dowel and the cross. The relationship between the maximum velocity of the wrist and the time at which grip aperture was maximal during the reach was highly consistent throughout the experiment. In contrast, the time of maximum grip aperture and maximum wrist velocity of the cerebellar patients was quite variable from trial to trial, and the relationship of these measurements also varied considerably. These abnormalities were present regardless of the accuracy requirement. In addition, the cerebellar patients required a significantly longer time to grasp and lift the objects than the control subjects. Furthermore, the patients exhibited a greater grip aperture during reach than the controls. These data indicate that the cerebellum contributes substantially to the coordination of movements required to perform reach-to-grasp movements. Specifically, the cerebellum is critical for executing this behavior with a consistent, well-timed relationship between the transport and grasp components. This contribution is apparent even when accuracy demands are minimal.

What and when: parallel and convergent processing in motor control

Successful motor behavior requires making appropriate response (response selection) at the right time (timing adjustment). Earlier psychological studies have suggested that the response selection and timing adjustment processes are performed serially in separate stages. We tested this hypothesis using functional magnetic resonance imaging. The subjects performed a choice reaction time task in four conditions: two (on-line response selection required or not) by two (on-line timing adjustment required or not). We found that the neural correlates for the two processes were indeed separate: the anterior medial premotor cortex (presupplementary motor area) was selectively active in response selection, whereas the cerebellar posterior lobe was selectively active in timing adjustment. However, the functional separation was only partial in that the lateral premotor cortex and the intraparietal sulcus were active equally for response selection and timing adjustment. The lateral premotor cortex was most active when both processes were required, suggesting that it integrates the information on response selection and the information on timing adjustment; alternatively, it might contribute to the allocation of attentional resources during dual information processing. The intraparietal sulcus was equally active when either response selection or timing adjustment was required, suggesting that it modifies, rather than integrates, these processes. Furthermore, our results suggest that these activations related to response selection and timing adjustment were distinct from sensory or motor processes.

Neural representation of a rhythm depends on its interval ratio

Rhythm is determined solely by the relationship between the time intervals of a series of events. Psychological studies have proposed two types of rhythm representation depending on the interval ratio of the rhythm: metrical and nonmetrical representation for rhythms formed with small integer ratios and noninteger ratios, respectively. We used functional magnetic resonance imaging to test whether there are two neural representations of rhythm depending on the interval ratio. The subjects performed a short-term memory task for a seven-tone rhythm sequence, which was formed with 1:2:4, 1:2:3, or 1:2.5:3.5 ratios. The brain activities during the memory delay period were measured and compared with those during the retention of a control tone sequence, which had constant intertone intervals. The results showed two patterns of brain activations; the left premotor and parietal areas and right cerebellar anterior lobe were active for 1:2:4 and 1:2:3 rhythms, whereas the right prefrontal, premotor, and parietal areas together with the bilateral cerebellar posterior lobe were active for 1:2.5:3.5 rhythm. Analysis on individual subjects revealed that these activation patterns depended on the ratio of the rhythms that were produced by the subjects rather than the ratio of the presented rhythms, suggesting that the observed activations reflected the internal representation of rhythm. These results suggested that there are two neural representations for rhythm depending on the interval ratio, which correspond to metrical and nonmetrical representations.

Speaking speed effects on delayed auditory feedback disruption of speech fluency

24 Italian medical students performed a task of verbal fluency. 12 students (the control group) receiving Normal Auditory Feedback and 12 students receiving Delayed Auditory Feedback (delay of 200 msec.) performed six trials in six different experimental settings: normal or increased speaking rate, and, for each condition, once with bilateral input of the auditory feedback, once to the right ear, and once to the left ear. At the normal speaking rate, the disruptive effect of delayed feedback was confirmed. As the speaking rate increased, the total number of errors increased within the control group but decreased within the group given delayed feedback, although the total number of errors was always greater for the latter. In addition, speech was more disrupted when the auditory input was returned to the right ear (left hemisphere) for all the different conditions: Normal and Delayed Auditory Feedback, normal and increased speaking rate. In particular, the left hemisphere was less resistant to the disruptive effect of the delayed feedback than the right hemisphere. From these results, we suggest that, when speaking more quickly, one uses more central mechanisms of movement programming (cortical-cerebellum-thalamus-cortical, cortical-corpus striatum-thalamus-cortical, and cortical-thalamus-cortical circuits), or attentional control (cortico-reticular-cortical circuits) than peripheral mechanisms (tactile, proprioceptive, and acoustic circuits). This may explain the decreased disruptive influence of delayed auditory feedback on speed, fluency, and quality at increased speaking rates. Hemispheric specialization processes, however, may explain the more pronounced susceptibility of the left hemisphere or the less pronounced susceptibility of the right hemisphere during the delayed feedback condition. In fact, the former processes phonemic, grammatical, and lexical features of words whilst the latter is competent in using metaphors and prosody in controlling the emotional aspects of language. Moreover, the right hemisphere is more active on attentional tasks.

Parallel neural networks for learning sequential procedures

Recent studies have shown that multiple brain areas contribute to different stages and aspects of procedural learning. On the basis of a series of studies using a sequence-learning task with trial-and-error, we propose a hypothetical scheme in which a sequential procedure is acquired independently by two cortical systems, one using spatial coordinates and the other using motor coordinates. They are active preferentially in the early and late stages of learning, respectively. Both of the two systems are supported by loop circuits formed with the basal ganglia and the cerebellum, the former for reward-based evaluation and the latter for processing of timing. The proposed neural architecture would operate in a flexible manner to acquire and execute multiple sequential procedures.

Organization of the human motor system as studied by functional magnetic resonance imaging

Blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI), because of its superior resolution and unlimited repeatability, can be particularly useful in studying functional aspects of the human motor system, especially plasticity, and somatotopic and temporal organization. In this survey, while describing studies that have reliably used BOLD fMRI to examine these aspects of the motor system, we also discuss studies that investigate the neural substrates underlying motor skill acquisition, motor imagery, production of motor sequences; effect of rate and force of movement on brain activation and hemispheric control of motor function. In the clinical realm, in addition to the presurgical evaluation of neurosurgical patients, BOLD fMRI has been used to explore the mechanisms underlying motor abnormalities in patients with neuropsychiatric disorders and the mechanisms underlying reorganization or plasticity of the motor system following a cerebral insult.