Cerebellar Subjects Research Articles

Additional somatosensory information does not improve cerebellar adaptation during catching

Objective: People with cerebellar damage are impaired in their ability to adapt anticipatory muscle activity during catching. We asked whether prior or on-line information about ball weight and drop height could improve the impaired adaptation of people with cerebellar damage. Methods: Cerebellar and control subjects caught a series of balls of different weights under two conditions. The first condition provided subjects with information about ball weight prior to the series of trials. The second condition provided subjects with information about ball weight, drop height, and time of ball release during the series of trials. Subjects had to maintain their hand within a vertical spatial ‘window’ during the catch. We measured 3-dimensional position and electromyography (EMG) from the catching arm. Results: With prior information, controls required a few trials to adapt to a new ball weight. Cerebellar subjects were slow, or unable, to adapt. With on-line information, controls were able to catch the ball within the window immediately, showing that they did not require practice to make this adjustment. Cerebellar subjects remained slow or unable to adapt to the changed ball weight even with on-line information. Conclusions: These results suggest that other, intact central nervous system structures cannot compensate for the role of the cerebellum in generating and adjusting anticipatory muscle activity across multiple joints.

Selection and coordination of human locomotor forms following cerebellar damage.

We have previously shown that control subjects use two distinct temporal strategies when stepping on an inclined surface during walking: one for level and 10 degrees surfaces and another for 20 and 30 degrees surfaces. These two temporal strategies were characterized by systematic shifts in the timing of muscle activity and peak joint angles. We examined whether cerebellar subjects with mild to moderate gait ataxia were impaired in their ability to select these two temporal strategies, adjust peak joint angle amplitudes, and/or adjust one joint appropriately with respect to movements and constraints at another joint. Subjects walked on a level surface and on different wedges (10, 20, and 30 degrees ) presented in the context of level walking. In a single trial, a subject walked on a level surface in approach to a wedge, took a single step on the wedge, and continued walking on an elevated level surface beyond the wedge. Cerebellar subjects used two temporal strategies, one for the level and 10 degrees surfaces and another for 20 and 30 degrees surfaces. Cerebellar strategies were similar to those used by controls except for the timing of ankle-joint movement on the steeper wedges. Cerebellar subjects adjusted the peak amplitudes of individual joint angles normally, with the exception of peak ankle plantarflexion. However, they exhibited greater trial-to-trial variability of peak hip and knee joint angles that increased as a function of wedge inclination. The most substantial deficit noted in the cerebellar group was in the relative movement of multiple joints. Cerebellar subjects demonstrated multijoint coordination deficits in all conditions, although these deficits were most pronounced during stance on the steeper wedges. On the 30 degrees wedge, cerebellar subjects showed abnormal relative movement of hip, knee, and ankle joints and the most substantial decomposition of movement. We speculate that to simplify multijoint control, cerebellar subjects decomposed their movement by fixing the ankle joint in a dorsiflexed position on the steepest wedges. Our results suggest that the cerebellum may not be critical in selecting the basic motor patterns for the two temporal strategies because cerebellar subjects produced appropriate timing shifts at most joints. Instead, our data suggest that the cerebellum is most critical for adjusting the relative movement of multiple joints, especially to accommodate external constraints.

The contribution of the cerebellum to speech processing

Lesions to or diseases of the cerebellum may disrupt the motor components of speech production both at the segmental and suprasegmental level giving rise to “ataxic dysarthria”, a syndrome characterized, among others, by slowed speaking rate, distorted consonant and vowel productions and impaired prosodic modulation of sentence utterances. The concept of ataxic dysarthria has been further refined by measurements at the acoustic speech signal, tracking of articulatory movements and preliminary functional imaging studies. In summary, the available parametric data indicate the cerebellum to support several aspects of speech processing: acceleration of orofacial gestures, timing (coordination) of complex articulatory sequences, presumably, in cooperation with the anterior perisylvian language zone and control of brainstem reflexes monitoring respiratory and laryngeal muscle activity. Lesion studies and functional imaging indicate superior aspects of the cerebellum to mediate the speech motor functions referred to. Laterality and extent of the respective representation area, presumably, depend upon task demands. Besides speech motor deficits, recent investigations found disrupted speech perception in cerebellar subjects in terms of impaired categorization of specific durational minimal pairs.

Cerebellar subjects show impaired adaptation of anticipatory EMG during catching.

We evaluated the role of the cerebellum in adapting anticipatory muscle activity during a multijointed catching task. Individuals with and without cerebellar damage caught a series of balls of different weights dropped from above. In Experiment 1 (light-heavy-light), each subject was required to catch light balls (baseline phase), heavy balls (adaptation phase), and then light balls again (postadaptation phase). Subjects were not told when the balls would be switched, and they were required to keep their hand within a vertical spatial "window" during the catch. During the series of trials, we measured three-dimensional (3-D) position and electromyogram (EMG) from the catching arm. We modeled the adaptation process using an exponential decay function; this model allowed us to dissociate adaptation from performance variability. Results from the position data show that cerebellar subjects did not adapt or adapted very slowly to the changed ball weight when compared with the control subjects. The cerebellar group required an average of 30.9 +/- 8.7 trials (mean +/- SE) to progress approximately two-thirds of the way through the adaptation compared with 1.7 +/- 0.2 trials for the control group. Only control subjects showed a negative aftereffect indicating storage of the adaptation. No difference in performance variability existed between the two groups. EMG data show that control subjects increased their anticipatory muscle activity in the flexor muscles of the arm to control the momentum of the ball at impact. Cerebellar subjects were unable to differentially increase the anticipatory muscle activity across three joints to perform the task successfully. In Experiment 2 (heavy-light-heavy), we tested to see whether the rate of adaptation changed when adapting to a light ball versus a heavy ball. Subjects caught the heavy balls (baseline phase), the light balls (adaptation phase), and then heavy balls again (postadaptation phase). Comparison of rates of adaptation between Experiment 1 and Experiment 2 showed that the rate of adaptation was unchanged whether adapting to a light ball or a heavy ball. Given these findings, we conclude that the cerebellum is important in generating the appropriate anticipatory muscle activity across multiple muscles and modifying it in response to changing demands though trial-and-error practice.

Phonemic Vowel Length Contrasts in Cerebellar Disorders

Apraxia of speech and Broca's aphasia both affect voice onset time (VOT) whereas phonemic vowel length distinctions seem to be preserved. Assuming a close cooperation of anterior perisylvian language zones and the cerebellum with respect to speech timing, a similar profile of segment durations must be expected in ataxic dysarthria. In order to test this hypothesis, patients with cerebellar atrophy or cerebellar ischemia were asked to produce sentence utterances including either one of the German lexial items “Rate” (/ra:the/, ‘installment’), “Ratte” (/rathe/, ‘rat’), “Gram” (/gra:m/, ‘grief’), “Gramm” (/gram/, ‘gramm’), “Taten” (/thatn/, ‘actions’), or “Daten” (/datn/, ‘data’). At the acoustic signal, the duration of the target vowels /a/ and /a:/ as well as the VOT of the word-initial alveolar stops /d/ and /t/ were determined. In addition, a master tape comprising the target words from patients and controls in randomized order was played to three listeners for perceptual evaluation. In accordance with a previous study, first, the cerebellar subjects presented with a reduced categorical separation of the VOT of voiced and unvoiced stop consonants. Second, vowel length distinctions were only compromised in case of the minimal pair “Gram”/“Gramm.” In contrast to “Rate”/“Ratte”, production of the former lexical items requires coordination of several orofacial structures. Disruption of vowel length contrasts would, thus, depend upon the complexity of the underlying articulatory pattern.

Voice Onset Time in Ataxic Dysarthria

In eight patients with a purely ataxic syndrome due to cerebellar atrophy the voice onset time (VOT) of word-initial stop consonants was measured at the acoustic signal. The subjects had been asked to produce sentence utterances including either one of the German minimal pair cognates “Daten” (/datən/, “data”) and “Taten” (/tatən/, “deeds”). In addition, a master tape comprising the target words from patients and controls in randomized order was played to six listeners for perceptual evaluation. Two major findings emerged. First, the cerebellar subjects presented with a reduced categorical distinction of the VOT of voiced and unvoiced stop consonants. Second, the patients' target words with initial unvoiced plosive gave rise to a significantly increased number of misassignments at perceptual evaluation. To some extent comparable VOT disruptions have been noted in apraxia of speech and basal ganglia disorders. Thus, different pathomechanisms might result in similar VOT abnormalities.

Cerebellar ataxia: abnormal control of interaction torques across multiple joints.

1. We studied seven subjects with cerebellar lesions and seven control subjects as they made reaching movements in the sagittal plane to a target directly in front of them. Reaches were made under three different conditions: 1) "slow-accurate," 2) "fast-accurate," and 3) "fast as possible." All subjects were videotaped moving in a sagittal plane with markers on the index finger, wrist, elbow, and shoulder. Marker positions were digitized and then used to calculate joint angles. For each of the shoulder, elbow and wrist joints, inverse dynamics equations based on a three-segment limb model were used to estimate the net torque (sum of components) and each of the component torques. The component torques consisted of the torque due to gravity, the dynamic interaction torques induced passively by the movement of the adjacent joint, and the torque produced by the muscles and passive tissue elements (sometimes called "residual" torque). 2. A kinematic analysis of the movement trajectory and the change in joint angles showed that the reaches of subjects with cerebellar lesions were abnormal compared with reaches of control subjects. In both the slow-accurate and fast-accurate conditions the cerebellar subjects made abnormally curved wrist paths; the curvature was greater in the slow-accurate condition. During the slow-accurate condition, cerebellar subjects showed target undershoot and tended to move one joint at a time (decomposition). During the fast-accurate reaches, the cerebellar subjects showed target overshoot. Additionally, in the fast-accurate condition, cerebellar subjects moved the joints at abnormal rates relative to one another, but the movements were less decomposed. Only three subjects were tested in the fast as possible condition; this condition was analyzed only to determine maximal reaching speeds of subjects with cerebellar lesions. Cerebellar subjects moved more slowly than controls in all three conditions. 3. A kinetic analysis of torques generated at each joint during the slow-accurate reaches and the fast-accurate reaches revealed that subjects with cerebellar lesions produced very different torque profiles compared with control subjects. In the slow-accurate condition, the cerebellar subjects produced abnormal elbow muscle torques that prevented the normal elbow extension early in the reach. In the fast-accurate condition, the cerebellar subjects produced inappropriate levels of shoulder muscle torque and also produced elbow muscle torques that did not very appropriately with the dynamic interaction torques that occurred at the elbow. Lack of appropriate muscle torque resulted in excessive contributions of the dynamic interaction torque during the fast-accurate reaches. 4. The inability to produce muscle torques that predict, accommodate, and compensate for the dynamic interaction torques appears to be an important cause of the classic kinematic deficits shown by cerebellar subjects during attempted reaching. These kinematic deficits include incoordination of the shoulder and the elbow joints, a curved trajectory, and overshoot. In the fast-accurate condition, cerebellar subjects often made inappropriate muscle torques relative to the dynamic interaction torques. Because of this, interaction torques often determined the pattern of incoordination of the elbow and shoulder that produced the curved trajectory and target overshoot. In the slow-accurate condition, we reason that the cerebellar subjects may use a decomposition strategy so as to simplify the movement and not have to control both joints simultaneously. From these results, we suggest that a major role of the cerebellum is in generating muscle torques at a joint that will predict the interaction torques being generated by other moving joints and compensate for them as they occur.

Interactions between the eye and hand motor systems: disruptions due to cerebellar dysfunction.

1. We tested the hypothesis that interactions occur between eye and hand movements produced in conjunction. This was accomplished by having human subjects with cerebellar dysfunction and age-matched controls perform two tasks: 1) tracking a moving target with the hand and 2) performing a pointing movement to intercept the target. Our prediction was that the inaccuracies that are characteristic of eye and hand movements generated in isolation by cerebellar subjects would be accentuated in each system during combined eye-hand tasks. 2. The cerebellar subjects took longer to respond to the onset of target motion in both tasks. This was true for both the eyes and hand, regardless of whether the eye and hand movements were generated in isolation or in conjunction with each other. 3. The cerebellar subjects also displayed a larger degree of error and/or variability in their hand movements than the control subjects. A significant amount of this increased variability was due to systematic changes in the trajectory of the hand during the critical periods leading up to and after each ocular saccade. These systematic changes were consistent with an overestimation of target velocity in the perifoveal visual field. 4. The increased variability of the cerebellar subjects' hand movements was markedly reduced by restricting eye movements. A similar reduction in variability occurred when vision of the hand was restricted in the tracking task. This effect was accompanied by improved eye movements. 5. For both sets of subjects the eye movements were affected by the hand movements produced in the tracking task. In particular, eye movement accuracy was improved in the controls and degraded in the cerebellar subjects when compared with the eye movements generated in isolation. In contrast, no changes were observed in the interception task. 6. Taken together, these results imply that a reciprocal interaction occurs between the eye and hand motor systems and/or that common "upstream" sites influence each of these systems in a similar manner. The functional anatomy and neurophysiological characteristics of several sites where such interactions may take place are discussed.

The control of voice onset time and vowel duration after paraneoplastic cerebellar degeneration: Correlation with regional cerebral glucose metabolism using positron emission tomography

In a companion report, an impairment in voice onset time (VOT) control was described for a group of subjects with paraneoplastic cerebellar degeneration who could otherwise produce appropriate segmental duration. The underlying neurophysiological changes were related to regional cerebral metabolic rates for glucose (rCMRGlu) determined by F18-fluorodeoxyglucose/positron emission tomography (PET). Nine cerebellar subjects and 18 normal controls were studied with eyes patched while listening to music and periodic verbal briefings. The rCMRGlu was calculated for each of 28 anatomically defined regions of interest (ROI). The cerebellar subjects could be differentiated from normals by their lower global metabolic rate, and by their rCMRGlu pattern. For those cerebellar subjects who could participate in the acoustic study, cerebellar rCMRGlu was significantly below normal range (p < 0.05) in all but one case. Severity of VOT abnormality appeared to be related not only to cerebellar rCMRGlu, but to abnormally low cortical rCMRGlu as well. The role of the cerebellum in maintaining temporal coordination of articulatory maneuvers appears to involve the coordination of cortical and subcortical brain regions. [Work supported by NS17778 and NS23473.]

The control of voice onset time and vowel duration after paraneoplastic cerebellar degeneration: An acoustic study

Speech production was examined in a group of six subjects with paraneoplastic cerebellar degeneration, a neurological disorder that produces severe dysarthria. Subjects were recorded repeating CVC and CVCV syllables that included the stop consonant [p b t d k g] and the vowels [i a u]. Vowel durations preceding voiced and voiceless segments and voice onset time (VOT) were measured. The vowel duration measures assessed the preservation of intrinsic duration properties, and the variation of these properties in conditioning phonological contexts. The VOT measure assessed the coordination of two independent articulatory events. Results indicated that the cerebellar subjects normally differentiated among individual vowels, and altered vowel duration as a function of phonological context. In contrast, they tended to reduce VOT for voiceless segments, and, in the case of the most impaired subject, the voiceless segments were always perceived as being voiced. Although the VOT durations were reduced, there was no overlap between voiced and voiceless VOTs for most cerebellar subjects. These results suggest that the temporal coordination of articulatory maneuvers rather than general timing of segmental duration may specifically involve the cerebellum. [Work supported by NS 17778.]