Biomedical subjects

H Poizner

Publications and source records attributed to H Poizner.

At least 19 recordsLinked to original sources

PubMed2001

Procedural motor learning in Parkinson's disease.

We have been investigating motor control and learning in parkinsonian subjects. In the current study, we sought to explore the existence of deficits in procedural motor learning, which is a form of implicit motor learning where skill improves over repetitive blocks of trials. We sought to determine, in particular, whether any such deficit is accentuated during specific types or phases of learning. We would expect that those specific learning tasks would require the greatest participation of the basal ganglia. Numerous studies have found that Parkinson's disease (PD) patients may show deficits in learning. Combined with information about basal ganglia neuronal connections and activity, this led some investigators to suggest that one of the key functions of the basal ganglia is to facilitate learning. To investigate these learning deficits, we used a robotic device to generate conservative force fields that disturbed the subjects' arm movements, thereby generating a "virtual mechanical environment" that subjects learned to manipulate. Movements were successively grouped into blocks comprising five different conditions: motor performance, early learning, late learning, negative transfer, and aftereffect motor performance. Our results with eight right-handed PD subjects and nine age-matched controls showed a relative decrease in the rate of learning for the PD patients in all blocks, but greater differences emerged between groups during novelty phases of learning. In particular, the difference in performance during the negative transfer condition reached statistical significance, suggesting that the basal ganglia might be a key center for "switching" motor patterns. Our results support the hypothesis that deficiencies in procedural motor learning are characteristic of PD. They add to existing evidence which has suggested a key role for the basal ganglia when new sensorimotor mappings are required by novel task environments. Better understanding of these deficits should facilitate the rehabilitation of PD patients.

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PubMed2001

Hand trajectory invariance in reaching movements involving the trunk.

Movements of different body segments may be combined in different ways to achieve the same motor goal. How this is accomplished by the nervous system was investigated by having subjects make fast pointing movements with the arm in combination with a forward bending of the trunk that was unexpectedly blocked in some trials. Subjects moved their hand above the surface of a table without vision from an initial position near the midline of the chest to remembered targets placed within the reach of the arm in either the ipsi- or contralateral workspace. In experiment 1, subjects were instructed to make fast arm movements to the target without corrections whether or not the trunk was arrested. Only minor changes were found in the hand trajectory and velocity profile in response to the trunk arrest, and these changes were seen only late in the movement. In contrast, the patterns of the interjoint coordination substantially changed in response to the trunk arrest, suggesting the presence of compensatory arm-trunk coordination minimizing the deflections from the hand trajectory regardless of whether the trunk is recruited or mechanically blocked. Changes in the arm interjoint coordination in response to the trunk arrest could be detected kinematically at a minimal latency of 50 ms. This finding suggests a rapid reflex compensatory mechanism driven by vestibular and/or proprioceptive afferent signals. In experiment 2, subjects were required, as soon as they perceived the trunk arrest, to change the hand motion to the same direction as that of the trunk. Under this instruction, subjects were able to initiate corrections only after the hand approached or reached the final position. Thus, centrally mediated compensatory corrections triggered in response to the trunk arrest were likely to occur too late to maintain the observed invariant hand trajectory in experiment 1. In experiment 3, subjects produced similar pointing movements, but to a target that moved together with the trunk. In these body-oriented pointing movements, the hand trajectories from trials in which the trunk was moving or arrested were substantially different. The same trajectories represented in a relative frame of reference moving with the trunk were virtually identical. We conclude that hand trajectory invariance can be produced in an external spatial (experiment 1) or an internal trunk-centered (experiment 3) frame of reference. The invariance in the external frame of reference is accomplished by active compensatory changes in the arm joint angles nullifying the influence of the trunk motion on the hand trajectory. We suggest that to make a transition to the internal frame of reference, control systems suppress this compensation. One of the hypotheses opened to further experimental testing is that the integration of additional (trunk) degrees of freedom into movement is based on afferent (proprioceptive, vestibular) signals stemming from the trunk motion and transmitted to the arm muscles.

Abdomen↗

PubMed2001

Automatic orienting of visuospatial attention in Parkinson's disease.

The basal ganglia are involved in not only motor behavior, but also other more cognitive processes, such as attention. We tested Parkinson's disease (PD) patients in a task that measures reflexive orienting of spatial attention. Seven patients with idiopathic PD and eight control subjects performed a covert orienting task where spatial attention was directed by means of exogenous cues (luminance increments) with no predictive validity for target position. The subjects' task was to make a speeded saccade to a visual target, which appeared a variable time after onset of the cue either in the cued or an uncued spatial position. There was no overall difference between PD patients and control subjects in terms of the initial facilitation following reflexive cues, and later inhibition of return (IOR). However, PD patients differed from control subjects in two important respects. First, they were significantly faster than were control subjects on this reflexive visual-orienting task. Second, disease severity correlated with attentional performance; more advanced patients showed less initial facilitation but greater IOR. Thus PD patients show better performance on a reflexive saccade task and, for more advanced patients, greater IOR than control subjects. These findings are consistent with the possibility that reflexive attentional processes in PD patients may be more active.

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PubMed2001

The interaction of visual and proprioceptive inputs in pointing to actual and remembered targets in Parkinson's disease.

We previously reported that Parkinson's disease patients could point with their eyes closed as accurately as normal subjects to targets in three-dimensional space that were initially presented with full vision. We have now further restricted visual information in order to more closely examine the individual and combined influences of visual information, proprioceptive feedback, and spatial working memory on the accuracy of Parkinson's disease patients. All trials were performed in the dark. A robot arm presented a target illuminated by a light-emitting diode at one of five randomly selected points composing a pyramidal array. Subjects attempted to "touch" the target location with their right finger in one smooth movement in three conditions: dark, no illumination of arm or target during movement; movement was to the remembered target location after the robot arm retracted; finger, a light-emitting diode on the pointing fingertip was visible during the movement but the target was extinguished; again, movement was to the remembered target location; and target, the target light-emitting diode remained in place and visible throughout the trial but there was no vision of the arm. In the finger condition, there is no need to use visual-proprioceptive integration, since the continuously visualized fingertip position can be compared to the remembered location of the visual target. In the target condition, the subject must integrate the current visible target with arm proprioception, while in the dark condition, the subject must integrate current proprioception from the arm with the remembered visual target. Parkinson's disease patients were significantly less accurate than controls in both the dark and target conditions, but as accurate as controls in the finger condition. Parkinson's disease patients, therefore, were selectively impaired in those conditions (target and dark) which required integration of visual and proprioceptive information in order to achieve accurate movements. In contrast, the patients' normal accuracy in the finger condition indicates that they had no substantial deficits in their relevant spatial working memory. Final arm configurations were significantly different in the two subject groups in all three conditions, even in the finger condition where mean movement endpoints were not significantly different. Variability of the movement endpoints was uniformly increased in Parkinson's disease patients across all three conditions. The current study supports an important role for the basal ganglia in the integration of proprioceptive signals with concurrent or remembered visual information that is needed to guide movements. This role can explain much of the patients' dependence on visual information for accuracy in targeted movements. It also underlines what may be an essential contribution of the basal ganglia to movement, the integration of afferent information that is initially processed through multiple, discrete modality-specific pathways, but which must be combined into a unified and continuously updated spatial model for effective, accurate movement.

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PubMed2001

Virtual reality-enhanced stroke rehabilitation.

A personal computer (PC)-based desktop virtual reality (VR) system was developed for rehabilitating hand function in stroke patients. The system uses two input devices, a CyberGlove and a Rutgers Master II-ND (RMII) force feedback glove, allowing user interaction with a virtual environment. This consists of four rehabilitation routines, each designed to exercise one specific parameter of hand movement: range, speed, fractionation or strength. The use of performance-based target levels is designed to increase patient motivation and individualize exercise difficulty to a patient's current state. Pilot clinical trials have been performed using the above system combined with noncomputer tasks, such as pegboard insertion or tracing of two-dimensional (2-D) patterns. Three chronic stroke patients used this rehabilitation protocol daily for two weeks. Objective measurements showed that each patient showed improvement on most of the hand parameters over the course of the training. Subjective evaluation by the patients was also positive. This technical report focuses on this newly developed technology for VR rehabilitation.

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PubMed2000

The timing of arm-trunk coordination is deficient and vision-dependent in Parkinson's patients during reaching movements.

The role of the basal ganglia in the coordination of different body segments and utilization of motor synergies was investigated by analyzing reaching movements to remembered three-dimensional (3D) targets in patients with Parkinson's disease (PD). Arm movements were produced alone or in combination with a forward bending of the trunk, with or without visual feedback. Movements in PD patients were more temporally segmented, as evidenced by irregular changes in tangential velocity profiles. In addition, the relative timing in the onsets and offsets of fingertip and trunk motions were substantially different in PD patients than in control subjects. While the control subjects synchronized both onsets and offsets, the PD patients had large mean intervals between the onsets and offsets of the fingertip and trunk motions. Moreover, PD patients showed substantially larger trial-to-trial variability in these intervals. The degree of synchronization in PD patients gradually increased during the movement under the influence of visual feedback. The mean and variability of the intersegmental intervals decreased as the fingertip approached the target. This improvement in timing occurred even though the separate variability in the timing of arm and trunk motions was not reduced by vision. In combined movements, even without vision, the PD patients were able to achieve normal accuracy, suggesting they were able to use the same movement synergies as normals to control the multiple degrees of freedom involved in the movements and to compensate for the added trunk movement. However, they were unable to recruit these synergies in the stereotyped manner characteristic of healthy subjects. These results suggest that the basal ganglia are involved in the temporal coordination of movement of different body segments and that related timing abnormalities may be partly compensated by vision. Abnormal intersegmental timing may be a highly sensitive indicator of a deficient ability to assemble complex movements in patients with basal-ganglia dysfunction. This abnormality may be apparent even when the overall movement goal of reaching a target is preserved and normal movement synergies appear to be largely intact.

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PubMed2000

A novel quantitative method for 3D measurement of Parkinsonian tremor.

OBJECTIVE: To demonstrate the usefulness of a three dimensional (3D) motion analysis system for the quantitative measurement of tremor in patients with Parkinson's disease (PD). METHODS: Six PD patients with hand tremors were studied using a system that employed 3D electromagnetic position sensors to measure the actual, cumulative displacement of the tremoring finger. Patients were studied in different hand positions and activating conditions before and 30, 60, 90 and 120 min after intake of Pramipexole, a dopamine agonist known to reduce tremor. Tremor amplitude and frequency, before and after drug intake, were compared using Mann-Whitney U test and Wilcoxon rank test, respectively. RESULTS: The motion analysis system allowed discrimination of tremor related events from movement artifact and allowed the calculation of real world movement of the finger tremor despite altered hand positions and orientation. Average 3D tremor frequency ranged from 3.71 to 4.34 Hz. Median tremor amplitude (total distance traveled per 5 s interval) decreased with drug from 4.9 to 1.6 cm for resting tremor, 4.5 to 3.7 cm for postural tremor, 3.4 to 3.3 cm for precision tremor, 10.2 to 3.3 cm for tapping activation and 108.6 to 5.7 cm for counting activation. CONCLUSIONS: Our method of 3D analysis provides a robust, single quantitative measure of tremor amplitude that is intuitive and likely to reflect the functional impact of tremor. This methodology should be useful in comparing tremor across patients and in measuring the efficacy of therapeutic interventions.

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PubMed1999

Articulatory consequences of Parkinson's disease: perspectives from two modalities.

Language production involves complex yet productively varying motor behavior. Rule-governed combinations yield a finite set of formational units combined in an infinite number of ways. The creativity of language ensures that no particular articulation will be highly automatized. Linguistic articulation is highly complex and varied. As such, it differs from the other more automatized motor behaviors typically studied such as learned movements in apraxia studies or repetitive behavior as occurs in walking or other everyday activities. Language also strives to maintain a balance between ease of articulation and ease of perception, while maintaining linguistically relevant distinctions. We report here a number of studies on the articulatory consequences of Parkinson's disease (PD) in the spoken and signed modalities. Our goal is to highlight the commonalities and distinctions between the two modalities of speech and sign that will allow us to better understand the impingements of PD on language production in general.

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PubMed1999

Apraxia differs in corticobasal degeneration and left-parietal stroke: A case study.

Corticobasal degeneration (CBD) is a progressive disorder characterized by both cortical and basal ganglia dysfunction such as asymmetrical apraxia, and akinetic rigidity, involuntary movements, and cortical sensory loss. Although apraxia is a key finding for the differential diagnosis of CBD, it has not been determined whether the features of apraxia seen in subjects with CBD are similar to those features exhibited by subjects with left-hemisphere damage from stroke. Therefore, for both clinical purposes and in order to better understand the brain mechanisms that lead to apraxia in CBD, we studied praxis in a patient with CBD and compared him to patients who are apraxic from left-parietal strokes. We used three-dimensional movement analyses to compare the features of apraxic movement. This subject with CBD was a dentist whose initial complaint had been that he "forgot" how to use his tools in the mouths of his patients. Analyses were performed on the trajectories made when using a knife to actually slice bread, and when repetitively gesturing slicing made to verbal command. Movements of the left hand, wrist, elbow, and shoulder were digitized in 3-D space. Although the CBD subject was clearly apraxic, the features of his apraxia differed markedly from those of the subjects with lesions in the left parietal lobe. For movements to command, the CBD subject showed joint coordination deficits, but his wrist trajectories were produced in the appropriate spatial plane, were correctly restricted to a single plane, and, like control subjects, were linear in path shape. However, when he was actually manipulating the tool and object, all of these aspects of his trajectories became impaired. In contrast, the deficits of the apraxic subjects with left-parietal damage were most pronounced to verbal command with their movements improving slightly although remaining impaired during actual tool and object manipulation. Unlike patients with parietal strokes, patients with CBD have degeneration in several systems and perhaps deficits in these other areas may account for the differences in praxic behavior.

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PubMed1999

Pointing in 3D space to remembered targets. II. Effects of movement speed toward kinesthetically defined targets.

The accuracy of visually guided pointing movements decreases with speed. We have shown that for movements to a visually defined remembered target, the variability of the final arm endpoint position does not depend on movement speed. We put forward a hypothesis that this observation can be explained by suggesting that movements directed at remembered targets are produced without ongoing corrections. In the present study, this hypothesis was tested for pointing movements in 3D space to kinesthetically defined remembered targets. Passive versus active acquisition of kinesthetic information was contrasted. Pointing errors, movement kinematics, and joint-angle coordination were analyzed. The movements were performed at a slow speed (average peak tangential velocity of about 1.2 m/s) and at a fast speed (2.7 m/s). No visual feedback was allowed during the target presentation or the movement. Variability in the final position of the arm endpoint did not increase with speed in either the active or the passive condition. Variability in the final values of the arm-orientation angles determining the position of the forearm and of the upper arm in space was also speed invariant. This invariance occurred despite the fact that angular velocities increased by a factor of two for all the angles involved. The speed-invariant variability supports the hypothesis that there is an absence of ongoing corrections for movements to remembered targets: in the case of a slower movement, where there is more time for movement correction, the final arm endpoint variability did not decrease. In contrast to variability in the final endpoint position, the variability in the peak tangential acceleration increased significantly with movement speed. This may imply that the nervous system adopts one of two strategies: either the final endpoint position is not encoded in terms of muscle torques or there is a special on-line mechanism that adjusts movement deceleration according to the muscle-torque variability at the initial stage of the movement. The final endpoint position was on average farther from the shoulder than the target. Constant radial-distance errors were speed dependent in both the active and the passive conditions. In the fast speed conditions, the radial distance overshoots of the targets increased. This increase in radial-distance overshoot with movement speed can be explained by the hypothesis that the final arm position is not predetermined in these experimental conditions, but is defined during the movement by a feedforward or feedback mechanism with an internal delay.

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PubMed1999

Control of voluntary and reflexive saccades in Parkinson's disease.

Eight patients with idiopathic Parkinson's disease (PD) were compared with a group of age-matched controls on both reflexive saccade and antisaccade tasks. While reflexive, visually guided saccades led to equivalent performance in both groups, PD patients were slower, made more errors, and showed reduced gain on antisaccades (AS). This is consistent with previous results showing that PD patients have no difficulty with reflexive saccades but show deficiencies in a number of voluntary saccade paradigms. Moreover, visual information in the form of landmarks improves AS performance more for PD patients than controls, a finding analogous to results seen with other motor acts such as target-directed pointing. Results are discussed in terms of a two-process model of attention and eye movements.

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PubMed1999

Crossed apraxia: implications for handedness.

Liepmann posited that right hand preference relates to left hemisphere dominance for learned skilled movements. Limb apraxia, impairment of skilled movement, typically occurs in individuals with left hemisphere (LH) lesions. The occurrence of apraxia in right-handed individuals following right-hemisphere lesions appears to refute Liepmann's hypothesis. We studied the apraxia of a right-handed man, RF, following a right frontal lesion to determine whether his apraxia paralleled the apraxia seen following LH lesions. Results of behavioral testing indicated that, like individuals with apraxia following left frontal lesions, RF was better at gesture recognition than gesture production which was significantly impaired across tasks. Kinematic motion analyses of movement linearity, planarity, and the coupling of temporospatial aspects of movements substantiated the parallel impairments in RF and patients with LH apraxia. The impairment seen in our patient with crossed apraxia provides evidence for the fractionation of systems underlying hand preference and skilled movement.

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PubMed1999

Interarticulator co-ordination in deaf signers with Parkinson's disease.

Motor control deficits in signers with Parkinson's disease (PD) were examined through analysis of their production of American Sign Language (ASL) fingerspelling, which is sequential and rapid motor behavior that has theoretical models of its underlying structure. Free conversation of two Deaf signers with PD and two Deaf control signers was analysed. In addition, scripted productions of one control signer were also analysed and directly compared to the same productions by the signers with PD. A featural analysis of ASL fingerspelling and a frame-by-frame analysis of multiple articulator movements were used to examine the fingerspelled productions. On the basis of the featural analysis, the signers with PD showed a variety of error patterns, all of which reflected attempts to reduce the motoric demands of coarticulation and thereby facilitate ease of articulation. Signers with PD either held individual segments in a fingerspelling sequence for a long time (segmentation), blended adjacent segments into a single segment (sequential blending), or broke handshapes down sequentially into their component features (featural unraveling). The results of both the featural analysis and the frame-by-frame analysis show that the PD signers have difficulty co-ordinating the movements of independent articulators in complex sequences. For example, the movements of independent articulators for fingerspelling (the thumb, fingers, and wrist) were markedly farther apart in time and more variable for the signers with PD. In addition, the signers with PD used fewer wrist movements while fingerspelling. Such deficits are consistent with claims that patients with PD are impaired in their ability to use ongoing sensorimotor information to program multi-articulator movements.

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PubMed1998

Chronic auditory agnosia following Landau-Kleffner syndrome: a 23 year outcome study.

We report a 27-year-old woman with chronic auditory agnosia following Landau-Kleffner Syndrome (LKS) diagnosed at age 4 1/2. She grew up in the hearing/speaking community with some exposure to manually coded English and American Sign Language (ASL). Manually coded (signed) English is her preferred mode of communication. Comprehension and production of spoken language remain severely compromised. Disruptions in auditory processing can be observed in tests of pitch and duration, suggesting that her disorder is not specific to language. Linguistic analysis of signed, spoken, and written English indicates her language system is intact but compromised because of impoverished input during the critical period for acquisition of spoken phonology. Specifically, although her sign language phonology is intact, spoken language phonology is markedly impaired. We argue that deprivation of auditory input during a period critical for the development of a phonological grammar and auditory-verbal short-term memory has limited her lexical and syntactic development in specific ways.

Adult↗

PubMed1998

Left hemispheric specialization for learned, skilled, and purposeful action.

Three-dimensional motion analyses were performed on trajectories of repetitive "slicing" gestures by 4 participants with left-hemisphere lesions and limb apraxia, 6 participants with right-hemisphere lesions, and 7 neurologically intact participants. Left hemispheric lesioned participants with apraxia, but not right hemispheric lesioned participants showed impaired coupling of spatial and temporal aspects of wrist trajectories and deficits in interjoint coordination. Both groups of brain-lesioned participants differed from control participants in the 3-D plane of the wrist motion. The deficits of some right hemispheric lesioned participants in controlling the plane of wrist motion may be a consequence of left hemispatial neglect with rightward deviations. In contrast, the deficits of apraxic participants in controlling wrist trajectories and coordinating joint motions seem to reflect a deficit in these participants for the movement plan.

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PubMed1998

Pointing to remembered targets in 3-D space in Parkinson's disease.

A three-dimensional tracking system was used to examine whether subjects with Parkinson's disease (PD) would show characteristic performance deficits in an unconstrained pointing task. Five targets were presented in a pyramidal array in space to 11 individuals with mild to moderate PD and 8 age-matched controls. After the target was indicated, subjects closed their eyes and pointed to the remembered target locations without vision. Despite the absence of visual feedback during movement, PD subjects were as accurate overall as controls. However, PD subjects showed greater variable errors, more irregular trajectories, and a vertical endpoint bias in which their endpoints were significantly lower than controls. They also showed deficiencies in the compensatory organization of joint rotations to ensure consistency in azimuthal (horizontal) positioning of the arm endpoint. We concluded that, under appropriate task conditions, PD subjects may not show overall deficits in accuracy even when making targeting movements at normal speed without visual feedback. Nevertheless, our findings indicate that there are certain dimensions of performance which are selectively altered in Parkinson's disease even when overall performance is normal.

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PubMed1998

Pointing in 3D space to remembered targets. I. Kinesthetic versus visual target presentation.

This study investigated the influence of different modalities of target information (visual, kinesthetic) on the accuracy, kinematics, and interjoint coordination of pointing movements to remembered targets. The targets were presented by a robot arm in five locations in three-dimensional (3D) space, either as a point of light in a dark room ("visual" condition), or kinesthetically. Relative pointing accuracy in the visual compared with kinesthetic conditions was influenced by the target location: pointing errors were the largest for the visual targets most eccentric relative to the subject's head. In addition, for the two most lateral targets, the final arm positions were, on average, closer to the center than the targets in the visual condition and farther from the center than the targets in the kinesthetic conditions. This result suggests that the pattern of errors in the visual condition described elsewhere ("range effect") may derive from visual processing rather than motor planning and implementation. Two modes of kinesthetic target presentation were utilized. During "passive" kinesthetic presentation of the target, the experimenter moved the subject's relaxed arm. Alternately, in "active" kinesthetic presentation of the target, the subject actively (with minimal help from the experimenter) moved his arm. No visual feedback was allowed in either kinesthetic condition. The variability in the final fingertip position was significantly smaller in the active condition than in the passive condition. In contrast, variability in the final values of arm orientation angles did not differ significantly in the active and passive conditions. This apparent contradiction may be resolved by the fact that, for the given target location, the influence of the deviation of these angles in the given trial from their average values on the position of the fingertip tended to be mutually compensated, and this tendency was stronger in the active condition. Our analysis of the correlations among the arm orientation angles and of the relationship between the initial and final arm configurations suggests that the kinesthetic conditions enabled the implementation of a mixture of strategies for achieving accuracy. The first strategy is to use a specific memory of an adequate arm configuration (that assumed during target presentation), such that accuracy is achieved by using this memory as a template. The second strategy is to use synergistically coordinating joint angles, such that accuracy is achieved by focusing on a specific endpoint that can be reached by a range of equivalent arm positions. The latter strategy was better utilized in the active condition. In conclusion, our results indicate that human subjects can use diverse sensory information to achieve comparable final accuracy, but that the details of the strategies employed differ with the kind of information available.

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PubMed1997

Visual-imitative dissociation apraxia.

Liepmann posited that, in right handers, the left parietal lobe contains movement formulas or representations. Therefore, performance failures may be induced by degraded representations, a failure of these representations to influence motor systems or a failure of stimuli to fully access these representations. Imitation may help the performance of subjects with degraded representations. However, patients who have impaired visual access to movement representations may perform more poorly with imitation than to verbal command. Trajectories of repetitive 'slicing' gestures made by a previously reported subject (Raymer et al.) with an infarction in the left visual association cortex (left occipital and inferior temporal lobe) that spared the parietal lobe were contrasted with those of three apraxic subjects with lesions that included the left parietal lobe and four non-brain-damaged control subjects. All subjects were asked to produce the gesture to verbal command and to imitation. Movements of the left hand, wrist, elbow and shoulder were digitized from neighboring views, reconstructed in three dimensions, and analysed graphically and numerically. The apraxic subjects with left parietal damage were unable to maintain the proper linearity and spatiotemporal attributes of their wrist motions and showed interjoint coordination deficits. Their deficits were most pronounced to verbal command, with their movements improving though remaining poorly performed when they imitated. The subject with the left occipital and inferior temporal lesion that spared parietal cortex, however, showed an opposite pattern. This subject exhibited close to normal performance when producing the movement to verbal command, but significant deficits when imitating.

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