Impaired capacity of cerebellar patients to perceive and learn two-dimensional shapes based on kinesthetic cues

Differential Effects of Parietal and Cerebellar Stroke in Response to Object Location Perturbation

BACKGROUND

The differential contributions of the cerebellum and parietal lobe to coordination between hand transport and hand shaping to an object have not been clearly identified.

OBJECTIVE

To contrast impairments in reach-to-grasp coordination, in response to object location perturbation, in patients with right parietal and cerebellar lesions, in order to further elucidate the role of each area in reach-to-grasp coordination.

METHOD

A two-factor design with one between subject factor (right parietal stroke; cerebellar stroke; controls) and one within subject factor (presence or absence of object location perturbation) examined correction processes used to maintain coordination between transport-to-grasp in the presence of perturbation. Sixteen chronic stroke participants (eight with right parietal lesions and eight with cerebellar lesions) were matched in age (mean = 61 years; standard deviation = 12) and hand dominance with 16 healthy controls. Hand and arm movements were recorded during unperturbed baseline trials (10) and unpredictable trials (60) in which the target was displaced to the left (10) or right (10) or remained fixed (40).

RESULTS

Cerebellar patients had a slowed response to perturbation with anticipatory hand opening, an increased number of aperture peaks and disruption to temporal coordination, and greater variability. Parietal participants also exhibited slowed movements, with increased number of aperture peaks, but in addition, increased the number of velocity peaks and had a longer wrist path trajectory due to difficulties planning the new transport goal and thus relying more on feedback control.

CONCLUSION

Patients with parietal or cerebellar lesions showed some similar and some contrasting deficits. The cerebellum was more dominant in controlling temporal coupling between transport and grasp components, and the parietal area was more concerned with using sensation to relate arm and hand state to target position.

Aging and curvature discrimination from static and dynamic touch

Two experiments evaluated the ability of 30 older and younger adults to discriminate the curvature of simple object surfaces from static and dynamic touch. The ages of the older adults ranged from 66 to 85 years, while those of the younger adults ranged from 20 to 29 years. For each participant in both experiments, the minimum curvature magnitude needed to reliably discriminate between convex and concave surfaces was determined. In Experiment 1, participants used static touch to make their judgments of curvature, while dynamic touch was used in Experiment 2. When static touch was used to discriminate curvature, a large effect of age occurred (the thresholds were 0.67 & 1.11/m for the younger and older participants, respectively). However, when participants used dynamic touch, there was no significant difference between the ability of younger and older participants to discriminate curvature (the thresholds were 0.58 & 0.59/m for the younger and older participants, respectively). The results of the current study demonstrate that while older adults can accurately discriminate surface curvature from dynamic touch, they possess significant impairments for static touch.

Does somatosensory discrimination activate different brain areas in children with unilateral cerebral palsy compared to typically developing children? An fMRI study

Aside from motor impairment, many children with unilateral cerebral palsy (CP) experience altered tactile, proprioceptive, and kinesthetic awareness. Sensory deficits are addressed in rehabilitation programs, which include somatosensory discrimination exercises. In contrast to adult stroke patients, data on brain activation, occurring during somatosensory discrimination exercises, are lacking in CP children. Therefore, this study investigated brain activation with functional magnetic resonance imaging (fMRI) during passively guided somatosensory discrimination exercises in 18 typically developing children (TD) (age, M=14 ± 1.92 years; 11 girls) and 16 CP children (age, M=15 ± 2.54 years; 8 girls). The demographic variables between both groups were not statistically different. An fMRI compatible robot guided the right index finger and performed pairs of unfamiliar geometric shapes in the air, which were judged on their equality. The control condition comprised discrimination of music fragments. Both groups exhibited significant activation (FDR, p<.05) in frontoparietal, temporal, cerebellar areas, and insula, similar to studies in adults. The frontal areas encompassed ventral premotor areas, left postcentral gyrus, and precentral gyrus; additional supplementary motor area (SMA proper) activation in TD; as well as dorsal premotor, and parietal operculum recruitment in CP. On uncorrected level, p<.001, TD children revealed more left frontal lobe, and right cerebellum activation, compared to CP children. Conversely, CP children activated the left dorsal cingulate gyrus to a greater extent than TD children. These data provide incentives to investigate the effect of somatosensory discrimination during rehabilitation in CP, on clinical outcome and brain plasticity.

Neuroscience findings on coordination of reaching to grasp an object: implications for research

BACKGROUND

Knowledge of how damage to brain regions and pathways affects central nervous system control of coordination of reach-to-grasp (RTG) following stroke may not be sufficiently used in existing treatment interventions or in research that assesses their effectiveness.

OBJECTIVE

To review current knowledge of motor control of coordination of RTG and discuss the extent to which this information is being used in research evaluating treatment interventions.

METHOD

This review (1) summarizes the current knowledge of motor control of RTG coordination in healthy individuals, including speculative models and structures of the brain identified as being involved; (2) summarizes evidence of RTG coordination deficits in people with stroke; (3) evaluates current interventions directed at retraining coordination of RTG, including a review of the extent to which these interventions are based on putative neurobiological mechanisms and reports on their effectiveness; and (4) recommends directions for research on treatment interventions for coordination of RTG.

RESULTS

Functional task-specific therapy, electrical stimulation, and robot or computerized training were identified as treatments targeted at improving coordination of RTG. However, none of the studies reporting the effect of these interventions related results to individual brain regions affected, and neurobiological mechanisms underlying improved performance were only minimally discussed.

CONCLUSIONS

Research on treatment interventions for coordination of RTG needs to combine measures of interruption to brain networks and how remaining intact neural tissue and networks respond to therapy with measures of spatiotemporal motor control and upper-limb function to gain a fuller understanding of treatment effects and their mechanisms.

An internal model architecture for novelty detection: implications for cerebellar and collicular roles in sensory processing

The cerebellum is thought to implement internal models for sensory prediction, but details of the underlying circuitry are currently obscure. We therefore investigated a specific example of internal-model based sensory prediction, namely detection of whisker contacts during whisking. Inputs from the vibrissae in rats can be affected by signals generated by whisker movement, a phenomenon also observable in whisking robots. Robot novelty-detection can be improved by adaptive noise-cancellation, in which an adaptive filter learns a forward model of the whisker plant that allows the sensory effects of whisking to be predicted and thus subtracted from the noisy sensory input. However, the forward model only uses information from an efference copy of the whisking commands. Here we show that the addition of sensory information from the whiskers allows the adaptive filter to learn a more complex internal model that performs more robustly than the forward model, particularly when the whisking-induced interference has a periodic structure. We then propose a neural equivalent of the circuitry required for adaptive novelty-detection in the robot, in which the role of the adaptive filter is carried out by the cerebellum, with the comparison of its output (an estimate of the self-induced interference) and the original vibrissal signal occurring in the superior colliculus, a structure noted for its central role in novelty detection. This proposal makes a specific prediction concerning the whisker-related functions of a region in cerebellar cortical zone A₂ that in rats receives climbing fibre input from the superior colliculus (via the inferior olive). This region has not been observed in non-whisking animals such as cats and primates, and its functional role in vibrissal processing has hitherto remained mysterious. Further investigation of this system may throw light on how cerebellar-based internal models could be used in broader sensory, motor and cognitive contexts.

Neural underpinning of postural responses to visual field motion

Numerous results emerging from current research strongly implicate the effect of Visual Field Motion on the organization of postural responses. However, this is the first empirical study exploring the neural substrates underlying the subjects' response to Visual Field Motion. Two separate experiments were conducted to investigate the subject responses to Visual Field Motion. In the first experiment, the standing subjects were exposed to Visual Field Motion in the VR environment. In the second experiment, the recumbent subjects viewed the same Visual Field Motion while in a MRI scanner. A virtual reality (VR) prototype of the moving room paradigm [Lee, D.N., Aronson, E., 1974. Visual proprioceptive control of standing in human infants. Perception & Psychophysics 15, 529-532] was developed to simulate various optic flow patterns in a controlled VR environment. Postural responses (center of pressure, body kinematics, vection, egomotion) and brain activation patterns (fMRI signals) were examined. The subjects experienced egomotion and have reported vection in both experiments only when certain attributes of Visual Field Motion were introduced. This was accompanied by significant activation of specific brain structures, including prefrontal, parietal cortices and bilateral cerebellum. We propose the existence of functional interactions between modality specific areas of the brain involved in postural responses to Visual Field Motion (VFM).

Identifying brain regions for integrative sensorimotor processing with ankle movements

The objective of this study was to define cortical and subcortical structures activated during both active and passive movements of the ankle, which have a fundamental role in the physiology of locomotion, to improve our understanding of brain sensorimotor integration. Sixteen healthy subjects, all right-foot dominant, performed a dorsi-plantar flexion task of the foot using a custom-made wooden manipulandum, which enabled measurements of the movement amplitude. All subjects underwent a training session, which included surface electromyography, and were able to relax completely during passive movements. Patterns of activation during active and passive movements and differences between functional MRI (fMRI) responses for the two types of movement were assessed. Regions of common activation during the active and passive movements were identified by conjunction analysis. We found that passive movements activated cortical regions that were usually similar in location to those activated by active movements, although the extent of the activations was more limited with passive movements. Active movements of both feet generated greater activation than passive movements in some regions (such as the ipsilateral primary motor cortex) identified in previous studies as being important for motor planning. Common activations during active and passive movements were found not only in the contralateral primary motor and sensory cortices, but also in the premotor cortical regions (such as the bilateral rolandic operculum and contralateral supplementary motor area), and in the subcortical regions (such as the ipsilateral cerebellum and contralateral putamen), suggesting that these regions participate in sensorimotor integration for ankle movements. In future, similar fMRI studies using passive movements have potential to elucidate abnormalities of sensorimotor integration in central nervous system diseases that affect motor function.

Identifying brain regions for integrative sensorimotor processing with ankle movements

The objective of this study was to define cortical and subcortical structures activated during both active and passive movements of the ankle, which have a fundamental role in the physiology of locomotion, to improve our understanding of brain sensorimotor integration. Sixteen healthy subjects, all right-foot dominant, performed a dorsi-plantar flexion task of the foot using a custom-made wooden manipulandum, which enabled measurements of the movement amplitude. All subjects underwent a training session, which included surface electromyography, and were able to relax completely during passive movements. Patterns of activation during active and passive movements and differences between functional MRI (fMRI) responses for the two types of movement were assessed. Regions of common activation during the active and passive movements were identified by conjunction analysis. We found that passive movements activated cortical regions that were usually similar in location to those activated by active movements, although the extent of the activations was more limited with passive movements. Active movements of both feet generated greater activation than passive movements in some regions (such as the ipsilateral primary motor cortex) identified in previous studies as being important for motor planning. Common activations during active and passive movements were found not only in the contralateral primary motor and sensory cortices, but also in the premotor cortical regions (such as the bilateral rolandic operculum and contralateral supplementary motor area), and in the subcortical regions (such as the ipsilateral cerebellum and contralateral putamen), suggesting that these regions participate in sensorimotor integration for ankle movements. In future, similar fMRI studies using passive movements have potential to elucidate abnormalities of sensorimotor integration in central nervous system diseases that affect motor function.

Learning of sensory sequences in cerebellar patients

A possible role of the cerebellum in detecting and recognizing event sequences has been proposed. The present study sought to determine whether patients with cerebellar lesions are impaired in the acquisition and discrimination of sequences of sensory stimuli of different modalities. A group of 26 cerebellar patients and 26 controls matched for age, sex, handedness, musicality, and level of education were tested. Auditory and visual sensory sequences were presented out of different sensory pattern categories (tones with different acoustic frequencies and durations, visual stimuli with different spatial locations and colors, sequential vision of irregular shapes) and different ranges of inter-cue time intervals (fast and slow). Motor requirements were small, with vocal responses and no time restrictions. Perception of visual and acoustic stimuli was generally preserved in patients and controls. The number of errors was significantly higher in the faster tempo of sequence presentation in learning of sequences of tones of different frequencies and in learning of sequences of visual stimuli of different spatial locations and different colors. No difference in tempo between the groups was shown. The total number of errors between the two groups was identical in the sequence conditions. No major disturbances in acquisition or discrimination of various sensory sequences were observed in the group of cerebellar patients. Sequence learning may be impaired only in tasks with significant motor demands.

How Self-Initiated Memorized Movements Become Automatic: A Functional MRI Study

We used functional magnetic resonance imaging (fMRI) and dual tasks to investigate the physiology of how movements become automatic. Normal subjects were asked to practice some self-initiated, self-paced, memorized sequential finger movements with different complexity until they could perform the tasks automatically. Automaticity was evaluated by having subjects perform a secondary task simultaneously with the sequential movements. Our secondary task was a letter-counting task where subjects were asked to identify the number of times a target letter from the letter sequences was seen. Only the performances that achieved high accuracy in both single and dual tasks were considered automatic. The fMRI results before and after automaticity was achieved were compared. Our data showed that for both conditions, sequential movements activated similar brain regions. No additional activity was observed in the automatic condition. There was less activity in bilateral cerebellum, presupplementary motor area, cingulate cortex, left caudate nucleus, premotor cortex, parietal cortex, and prefrontal cortex during the automatic stage. These findings suggest that most of the motor network participates in executing automatic movements and that it becomes more efficient as movements become more automatic. Our results do not provide evidence for any area to become more activated for automatic movements.

Cerebellar activation during copying geometrical shapes

We studied functional MRI activation in the cerebellum during copying 9 geometrical shapes (equilateral triangle, isosceles triangle, square, diamond, vertical trapezoid, pentagon, hexagon, circle, and vertical lemniscate). Twenty subjects were imaged during 3 consecutive 45-s periods (rest, visual presentation, and copying). First, there was a positive relation between cerebellar activation and the peak speed of individual movements. This effect was strongest in the lateral and posterior ipsilateral cerebellum but it was also present in the paramedian zones of both cerebellar hemispheres and in the vermis. A finer grain analysis of the relations between the time course of the blood oxygenation level-dependent activation and movement parameters revealed a significant relation to hand position and speed but not to acceleration. Second, there was a significant relation between the intensity of voxel activation during visual presentation and the speed of the upcoming movement. The spatial distribution of these voxels was very similar to that of the voxels activated during copying, indicating that the cerebellum might be involved in motor rehearsal, in addition to its role during movement execution. Finally, a factor analysis of the intensity of activated voxels in the ipsilateral cerebellum during copying (adjusted for the speed effect) extracted 3 shape factors. Factor 1 reflected "roundness," factor 2 "upward pointing," and factor 3 "pointing (up or down) and elongation." These results link cerebellar activation to more global, spatial aspects of copying.

Task-dependent role of the cerebellum in motor learning

This chapter reviews several findings from our laboratory supporting the hypothesis that the cerebellum's role in motor learning is task-dependent. Namely, its contribution is dependent on the specific task being learned. Several studies are reviewed to demonstrate that the effect of temporary or permanent cerebellar lesions on a specific process such as storage varies depending on the behavior. Furthermore, this task-dependency is reflected also in the modulation of Purkinje cells and nuclear neurons recorded during the learning process. The behavioral correlates of this modulation are very paradigm specific. These observations support the above hypothesis and emphasize the importance of paradigm selection in designing experiments focused on elucidating the cerebellum's role in learning a specific motor behavior.

On-line compensation for perturbations of a reaching movement is cerebellar dependent: support for the task dependency hypothesis

Although the cerebellum has been shown to be critical for the acquisition and retention of adaptive modifications in certain reflex behaviors, this structure's role in the learning of motor skills required to execute complex voluntary goal-directed movements still is unclear. This study explores this issue by analyzing the effects of inactivating the interposed and dentate cerebellar nuclei on the adaptation required to compensate for an external elastic load applied during a reaching movement. We show that cats with these nuclei inactivated can adapt to predictable perturbations of the forelimb during a goal-directed reach by including a compensatory component in the motor plan prior to movement initiation. In contrast, when comparable compensatory modifications must be triggered on-line because the perturbations are applied in randomized trials (i.e., unpredictably), such adaptive responses cannot be executed or reacquired after the interposed and dentate nuclei are inactivated. These findings provide the first demonstration of the condition-dependent nature of the cerebellum's contribution to the learning of a specific volitional task.

Bias and sensitivity in the haptic perception of geometry

Our ability to recognize and manipulate objects relies on our haptic sense of the objects' geometry. But little is known about the acuity of haptic perception compared to other senses like sight and hearing. Here, we determined how accurately humans could sense various geometric features of objects across the workspace. Subjects gripped the handle of a robot arm which was programmed to keep the hand inside a planar region with straight or curved boundaries. With eyes closed, subjects moved the manipulandum along this virtual wall and judged its curvature or direction. We mapped their sensitivity in different parts of the workspace. We also tested subjects' ability to discriminate between boundaries with different degrees of curvature, to sense the rate of change of curvature, and to detect the elongation or flattening of ellipses. We found that subjects' estimates of the curvature of their hand path were close to veridical, and did not change across the workspace though they did vary somewhat with hand path direction. Subjects were less accurate at judging the direction of the hand path in an egocentric frame of reference, and were slightly poorer at discriminating between arcs of different curvature than at detecting absolute curvature. They also consistently mistook flattened ellipses and paths of decreasing curvature (inward spirals) for circles-and mistook arcs of true circles for arcs of tall ellipses or outward spirals. Nevertheless, the sensitivity of haptic perception compared well with that of spatial vision in other studies. Furthermore, subjects detected curvature and directional deviations much smaller than those that actually arise for most reaching movements. These findings suggest that our haptic sense is acute enough to guide and train motor systems and to form accurate representations of shapes.

Stimulation in the rat fastigial nucleus enhances the responses of neurons in the dorsal column nuclei to innocuous stimuli

The cerebellum was recently proposed to play a role in cognition and sensation in addition to motor phenomena. We have shown that the cerebellum is involved in the processing of sensory nociceptive information. In this study, the activity of neurons in the dorsal column nuclei (DCN) was tested following stimulation in the rat fastigial nucleus. The results showed an enhancement of the extracellularly recorded responses of DCN neurons to somatic non-noxious stimuli following injection of D,L-homocysteic acid (0.1 M, 1 microl) into the area of the fastigial nucleus. We conclude that the cerebellum influences the processing of non-noxious somatosensory information at the level of the DCN, an important relay and a center for the processing of fine tactile and vibratory information. This observation is not yet supported by clinical data.

Cerebellar damage impairs automaticity of a recently practiced movement

It has been suggested that the cerebellum plays a critical role in learning to make movements more "automatic" (i.e., requiring less attention to the details of a movement). We hypothesized that cerebellar damage compromises learning of movement automaticity, resulting in increased attentional demands for movement control. The purpose of our study was to determine whether cerebellar damage disrupts the ability to make a practiced movement more automatic. We developed a dual task paradigm using two tasks that did not have overlapping sensory or motor requirements for execution. Our motor task required subjects to maintain an upright posture while performing a figure-8 movement using their arm. This motor task was chosen to simulate requirements of everyday movements (e.g., standing while reaching for objects), but it was novel enough to require practice for improvement. Our secondary task was an auditory vigilance task where subjects listened to letter sequences and were asked to identify the number of times a target letter was heard. We tested controls and people with cerebellar damage as they practiced the movement task alone and then performed it with the auditory task. We recorded 3D position data from the arm, trunk, and leg during the movement task. Errors were recorded for both the movement and the letter tasks. Our results show that cerebellar subjects can improve the movement to a very limited extent with practice. Unlike controls, the motor performance of cerebellar subjects deteriorates to prepractice levels when attention is focused away from the movement during dual task trials. Control subjects' insensitivity to dual task interference after practice was due to learned movement automaticity and was not a reflection of better dual task performance generally. Overall, our findings suggest that the cerebellum may be important for shifting movement performance from an attentionally demanding (unpracticed) state to a more automatic (practiced) state.

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.

Generative character of perception: a neural architecture for sensorimotor anticipation

The basic idea of our anticipatory approach to perception is to avoid the common separation of perception and generation of behavior and to fuse both aspects into a consistent neural process. Our approach tries to explain the phenomenon of perception, in particular, of perception at the level of sensorimotor intelligence, from a behavior-oriented point of view. Perception is assumed to be a generative process of anticipating the course of events resulting from alternative sequences of hypothetically executed actions. By means of this sensorimotor anticipation, it is possible to characterize a visual scenery immediately in categories of behavior, i.e. by a set of actions which describe possible methods of interaction with the objects in the environment. Thus, the competence to perceive a complex situation can be understood as the capability to anticipate the course of events caused by different action sequences. Starting from an abstract description of anticipatory perception and the essential biological evidence for internal simulation, we present two biologically motivated computational models that are able to anticipate and evaluate hypothetically sensorimotor sequences. Both models consider functional aspects of those cortical and subcortical systems that are assumed to be involved in the process of sensory prediction and sensorimotor control. Our first approach, the Model for Anticipation based on Sensory IMagination (MASIM), realizes a sequential search in sensorimotor space using a simple model of lateral cerebellum as sensory predictor. We demonstrate the efficiency of this model approach in the light of visually guided local navigation behaviors of a mobile system. The second approach, the Model for Anticipation based on Cortical Representations (MACOR), is actually still at a conceptual level of realization. We postulate that this model allows a completely parallel search at the neocortical level using assemblies of spiking neurons for grouping, separation, and selection of sensorimotor sequences. Both models are intended as general schemes for anticipation based perception at the level of sensorimotor intelligence.