Biomedical subjects

J Hermsdörfer

Publications and source records attributed to J Hermsdörfer.

At least 19 recordsLinked to original sources

PubMed2005

Force level independent representations of predictive grip force-load force coupling: a PET activation study.

The existence of forward internal models is a fundamental principle in theories of predictive motor control. There are indications that internal models are represented in the cerebellum. So far, no conclusive data exist on automated procedures involving predictive motor behavior. In particular, it is unknown whether single or multiple task-specific internal models handle the broad range of behavioral situations in which they occur. Using H2(15)O PET in eight subjects, we examined predictive motor control in an automated grip force-load force coupling task at three differing load force levels. In the experimental condition, subjects pulled a grasped object against an isometric resistance while simultaneously producing anticipatory grip forces. There were three control conditions (pull force isolated; grip force isolated; motor rest). A 2 x 2 factorial design was chosen to reveal the interaction effect of grip force-pull force coupling. The factors were pull force (with/without) and grip force (with/without). Grip and load forces were well matched between experimental and control conditions. Conjunction inference and interaction analyses identified force coupling related activity in the ipsilateral posterior cerebellum that was independent of force levels. Interaction effects were also identified in the anterior cingulate and frontal association regions, the right caudate nucleus, and the left lingual gyrus. These data demonstrate the existence of modular representations for predictive force coupling, with the ipsilateral cerebellum playing a major role. Moreover, the data implicate that the representations for predictive force control are applicable to a range of different environmental affordances.

Brain↗

PubMed2004

The effect of tactile feedback on pantomime of tool use in apraxia.

OBJECTIVE: To investigate whether apraxic patients' better performance with real tools compared to miming is due to the tactile feedback provided by holding the tool. METHODS: Ten patients with aphasia and apraxia from left hemisphere damage were asked to demonstrate the use of 12 tools and objects under three conditions: miming with empty hands, miming with an implement shaped like the handle of the tool, and using the real tool with its corresponding object. RESULTS: Whereas real tool use was much better than pantomime in all patients, tactile feedback from the isolated handle facilitated miming only in some and deteriorated it in others so that across the group there was no significant improvement. CONCLUSIONS: The better performance of real than of pretended tool use does not depend on tactile feedback per se, but on the mechanical affordances and constraints of tools and objects transmitted by this feedback in real use. Tactile feedback deprived of these contents and restricted to the shape of the handle does not substantially help produce the appropriate action.

Adult↗

PubMed2003

Digit cooling influences grasp efficiency during manipulative tasks.

A commonly experienced effect of cold is a sensation of numbness and loss of sensibility in the fingers. Intact tactile sensibility of the grasping digits is essential for the efficient scaling of grip force level during the manipulation of hand-held objects. We investigated whether or not cooling of the grasping digits affects scaling of the grip force magnitude in relation to the loads resulting from continuous vertical arm movements performed with a grasped instrumented object. Maxima and minima of load force occurred at the lower and upper turning point of the movement cycle, respectively, and were accompanied by maximum and minimum peaks in grip force occurring close in time prior to and following digit cooling, respectively. Thus, digit cooling did not influence the ability to adjust the grip force profile in anticipation of movement-induced fluctuations in load force. However, subjects established significantly higher grip forces against the hand-held object following digit cooling and generated a 10-70% higher ratio between grip and load forces at the upper and lower turning points of the movement cycle. It is thought that the impaired economical scaling of grip force level is the result of reduced sensory feedback from the grasping fingers during digit cooling. The results provide further evidence to support the suggestion that cutaneous afferent input plays a subordinate role in the predictive temporal regulation of the grip force profile, but is used to adapt economically the force level to the actual loading requirements during dynamic object manipulation.

Acceleration↗

PubMed2003

The dependence of ipsilesional aiming deficits on task demands, lesioned hemisphere, and apraxia.

Neuroimaging studies as well as neurophysiological and lesion data indicate that the ipsilateral hemisphere plays a role in controlling the active limb. However, the nature and the conditions of this ipsilateral control are not well understood. We measured aiming movements with the ipsilesional limb toward targets with different characteristics which were made by patients with unilateral left brain damage (LBD) or right brain damage (RBD). The movement kinematics were analysed. Performance measures of the pointing movements were impaired in LBD patients, whereas RBD patients performed normally. LBD patients had obvious deficits during all tasks; however, they were exacerbated when high accuracy was required, and when an exocentric target had to be reached without visual feedback. Thus, the motor-dominant hemisphere plays a specific role in the programming and execution of ipsilateral aiming movements, and the importance of ipsilateral control increases with increasing task demands. To assess the relationship between pointing deficits and apraxia in LBD patients, the imitation of meaning gestures was tested. We replicated a recent study, showing that deviations of the final hand position from the demonstration were not correlated with abnormal kinematics of the corresponding arm movement when LBD patients performed this test. However, there were correlations between related kinematic measures during pointing and gesture imitation. These findings suggest a deficit of motor programming and execution after damage to the motor-dominant brain which is unrelated to the spatial errors characteristic of apraxia. This deficit affects different types of goal-directed aiming movements and its severity depends on task demands.

Adult↗

PubMed2003

Grip force control during object manipulation in cerebral stroke.

OBJECTIVE: To analyze impairments of manipulative grip force control in patients with chronic cerebral stroke and relate deficits to more elementary aspects of force and grip control. METHODS: Nineteen chronic stroke patients with fine motor deficits after unilateral cerebral lesions were examined when performing 3 manipulative tasks consisting of stationary holding, transport, and vertical cyclic movements of an instrumented object. Technical sensors measured the grip force used to stabilize the object in the hand and the object accelerations, from which the dynamic loads were calculated. RESULTS: Many patients produced exaggerated grip forces with their affected hand in all types of manipulations. The amount of finger displacement in a grip perturbation task emerged as a highly sensitive measure for predicting the force increases. Measures of grip strength and maximum speed of force changes could not account for the impairments with comparable accuracy. In addition to force economy, the precision of the coupling between grip and load forces was impaired. However, no temporal delays were typically observed between the grip and load force profiles during cyclic movements. CONCLUSIONS: Impaired sensibility and sensorimotor processing, evident by delayed reactions in the perturbation task, lead to an excessive increase of the safety margin between the actual grip force and the minimum force necessary to prevent object slipping. In addition to grip force scaling, cortical sensorimotor areas are responsible for smoothly and precisely adjusting grip forces to loads according to predictions about movement-induced loads and sensory experiences. However, the basic feedforward mechanism of grip force control by internal models appears to be preserved, and thus may not be a cortical but rather a subcortical or cerebellar function, as has been suggested previously.

Adult↗

PubMed2002

Ipsilesional deficits during fast diadochokinetic hand movements following unilateral brain damage.

Impaired sensorimotor function of the hand ipsilateral to a unilateral brain lesion has been reported in a variety of motor tasks; however, elementary diadochokinetic movements, such as tapping with the index finger, seem to be preserved in chronic-lesion patients. Three different diadochokinetic movements (forearm diadochokinesis, hand tapping (HT) and finger tapping (FT)) were tested in patients with left brain damage (LBD) and right brain damage (RBD) and control subjects. Movements were measured three-dimensionally and the kinematics of joint angles were analyzed. While the patients' measures of movement speed and symmetry appeared normal, detailed kinematic analysis revealed clear deficits in several measures of movement variability, which reflected decreased regularity of the alternating movement cycles. This impairment was greater in LBD patients and tended to be greater during forearm diadochokinesis. The necessity of ipsilateral control in addition to dominant, contralateral control, especially during left hand and more complex or more proximal manual tasks may account for these findings. In addition, the role of apraxia (defined by impairments during the imitation of gestures) in the performance deficits of LBD patients was also assessed. Although, some performance decrements were associated with the presence of apraxia, these were different from the group findings and restricted to the two tapping tasks. Thus, although apraxia may have caused deficits in establishing dynamic representations of the elementary postures in conditions of high speed and low complexity, the disturbances during diadochokinetic movements must for the most part be attributed to more motor-related deficits of ipsilateral sensorimotor control, which are particularly apparent when the motor dominant left hemisphere is affected. The absence of clear correlations between performance deficits and lesion characteristics suggests that a distributed network is involved in this ipsilateral control.

Adult↗

PubMed2001

Cortical correlates of gesture processing: clues to the cerebral mechanisms underlying apraxia during the imitation of meaningless gestures.

The clinical test of imitation of meaningless gestures is highly sensitive in revealing limb apraxia after dominant left brain damage. To relate lesion locations in apraxic patients to functional brain activation and to reveal the neuronal network subserving gesture representation, repeated H2(15O)-PET measurements were made in seven healthy subjects during a gesture discrimination task. Observing paired images of either meaningless hand or meaningless finger gestures, subjects had to indicate whether they were identical or different. As a control condition subjects simply had to indicate whether two portrayed persons were identical or not. Brain activity during the discrimination of hand gestures was strongly lateralized to the left hemisphere, a prominent peak activation being localized within the inferior parietal cortex (BA40). The discrimination of finger gestures induced a more symmetrical activation and rCBF peaks in the right intraparietal sulcus and in medial visual association areas (BA18/19). Two additional foci of prominent rCBF increase were found. One focus was located at the left lateral occipitotemporal junction (BA 19/37) and was related to both tasks; the other in the pre-SMA was particularly related to hand gestures. The pattern of task-dependent activation corresponds closely to the predictions made from the clinical findings, and underlines the left brain dominance for meaningless hand gestures and the critical involvement of the parietal cortex. The lateral visual association areas appear to support first stages of gesture representation, and the parietal cortex is part of the dorsal action stream. Finger gestures may require in addition precise visual analysis and spatial attention enabled by occipital and right intraparietal activity. Pre-SMA activity during the perception of hand gestures may reflect engagement of a network that is intimately related to gesture execution.

Adult↗

PubMed2001

Human development of grip force modulation relating to cyclic movement-induced inertial loads.

The present study examines the development of grip force modulation relating to self-induced loads during repetitive vertical arm movements at different frequencies with a hand-held object. One hundred and thirty-four 3- to 6-year-old children and 16 adults were asked to move a lightweight object up and down at increasing rates from 0.5 Hz up to individual maximal arm movement rates (> 2.5 Hz). Grip forces were measured by a uni-axial force transducer and the inertial forces (tangential forces) were calculated from the measurements by accelerometers within the object. Generally, the quality of anticipatory grip force control improved from movement frequencies of 1 Hz to 2.5 Hz and decreased above 2.5 Hz. At movement frequencies below 1 Hz, the phase lag between grip and load force cycles was longer in children than in adults (children: median = 17 ms; adults: median = 0 ms); however, there were no significant differences between the age groups above 1.5 Hz. The grip-to-load force ratio and the grip force modulation were not significantly different from the adults up to 2.5 Hz. The fine coupling of grip and load forces (precise temporal and gain control) showed age effects among the 3- to 6-year-old children, mainly between 3- and 4-year-olds, and in adults extremely good coupling at medium arm movement frequencies. However, concerning the pure temporal coordination of grip and inertial forces, there were only differences between the 3-year-old children and the other groups at arm movement frequencies above 2.5 Hz. The results show that, during cyclic movements with hand-held loads, temporal control is well established at the age of 4 years whereas the fine gain control needs a longer time to develop. The anticipatory control is dependent on the arm movement frequency and, therefore, how rapidly the inertial loads change. The high level of anticipatory control during self-induced repetitive actions in children of 3-6 years of age is interpreted as an early developing ability to predict precisely cyclic self-induced inertial loads of hand-held objects when the object properties are known by proprioception. The timing, which is possibly related to cerebellar functions, is, to some extent, developed earlier than the gain control, which may be associated with cortical functions.

Adult↗

PubMed2001

Imitation of gestures by disconnected hemispheres.

PU's corpus callosum was severed as a sequel of bleeding from an arteriovenous malformation. The lesion affects the truncus and the splenium and caused somatosensory and visual disconnection of the hemispheres. On clinical testing PU's left hand was apraxic for pantomime of object use but not for imitation. By contrast, when stimuli for imitation of meaningless hand and finger postures were presented tachistocopically to either the left or the right visual field, both hemispheres turned out to be apraxic in different ways. Imitation of hand postures was perfect for right-handed imitation of stimuli presented to the left hemisphere but defective in all other conditions. Imitation of finger postures was below the normal range in all conditions initially, but improved to normality for right-hand imitation of stimuli presented to the left hemisphere after repeated testing. After successful imitation of gestures presented to the left hemisphere PU commented that he imitated without really seeing the stimulus by "formulating the unseen", whereas after presentation to the right hemisphere he felt that he saw the stimulus but could not imitate. We propose that imitation of meaningless gestures affords a coding of gestures with reference to knowledge about body parts which can be applied only by the left hemisphere. Imitation of finger postures puts additional demands on fine grained visuospatial discrimination which necessitates a contribution by the right hemisphere.

Adult↗

PubMed2001

The effects of digital anaesthesia on predictive grip force adjustments during vertical movements of a grasped object.

Grip force adjustments to fluctuations of inertial loads induced by vertical arm movements with a grasped object were analysed during normal and impaired finger sensibility. Normally grip force is modulated in a highly economical way in parallel with fluctuations of load force. Two subjects performed vertical up and down movements of a grasped object, both with normal finger sensibility and then cutaneously anaesthetized finger sensibility. Short breaks were taken in between single movements, during which the object was held stationary. After digital anaesthesia was applied to the grasping fingers, both subjects substantially increased the grip force. The grip force amplitude and timing still anticipated changes in load force, although the established grip force had already overcome movement-induced load force peaks. This implies that the increase of grip force and consequently the elevated force ratio between maximum grip and maximum load force are not processed to alter the feedforward system of grip force control. Cutaneous afferent information from the grasping digits appears to be necessary for economic scaling of the grip force level, but it plays a subordinate role in the precise anticipatory temporal coupling of grip and load forces during voluntary object manipulation.

Adult↗

PubMed2001

Effects of changing gravity on anticipatory grip force control during point-to-point movements of a hand-held object.

We investigated the quality of predictive grip force control during gravity changes induced by parabolic flight maneuvers. During these maneuvers gravity varied: There were 2 periods of hypergravity, in which terrestrial gravity nearly doubled, and a 20-s period of microgravity, during which a manipulated object was virtually weightless. We determined grip and load forces during vertical point-to-point movements of an instrumented object. Point-to-point movements were a combination of static (stationary holding) and dynamic (continuous movements) task conditions, which were separately analyzed in our previous studies. Analysis of the produced grip forces revealed that grip adjustments were closely linked to load force fluctuations under each gravity condition. In particular, grip force maxima coincided closely in time with load force peaks, although these occurred at different phases of the movement depending on the gravity level. However, quantitative analysis of the ratio of maximum grip force to the corresponding load force peak revealed an increased force ratio during microgravity when compared to that during normal and hypergravity. We hypothesize that the impaired precision of force coupling with respect to force magnitude during microgravity results from reduced feedback information about the object's mass during the stationary holding of the object in between each movement. The results indicate that the temporal grip force regulation is highly automatized and stable, whereas economical planning of force magnitude is more flexible and might reflect changes of the external loading condition.

Adaptation, Physiological↗

PubMed2000

A system for the study of visuomotor coordination during reaching for moving targets.

Prehensile behavior is a popular task in current research on human motor control. Most studies on reaching used stationary target objects and, therefore, most models do not address the challenges the motor system must respond to when reaching for moving objects. The machines used in earlier studies to produce object motion offered a limited range of trajectories and restricted control over various movement parameters. We have developed a device that allows a great variety of object trajectories along a flat-table surface and gives the experimenter full control over all movement parameters. A linear positioning system is used to move a sled beneath the table surface. Magnetic coupling transfers the sled's movement to the target object on the tabletop. This arrangement allows fast movements of the object (up to 5 m/s) and at the same time protects subjects from any harm due to the moving parts. The system is connected to LC shutter glasses, a 3-D movement registration device, and a switch that detects the onset of hand motion. This allows the selective withdrawal of vision during the reaching task or the introduction of changes in the object motion depending on the subject's reactions.

Electronic Data Processing↗

PubMed2000

Moving weightless objects. Grip force control during microgravity.

When we move grasped objects, our grip force precisely anticipates gravitational and inertial loads. We analysed the control of grip forces during very substantial load changes induced by parabolic flights. During these flight manoeuvres, the gravity varies between hypergravity associated with a doubling of normal terrestrial gravity and a 20-s period of microgravity. Accordingly, the contribution of the object's weight to the load changed from being twice the normal value to being absent. Two subjects continuously performed vertical and horizontal movements of an object equipped with grip force and acceleration sensors. Whereas, during vertical movements performed under normal and hypergravity, a load force maximum occurred at the lower turning point and a minimum at the upper turning point, the load force pattern was completely changed under microgravity. In particular, the upper turning point was also associated with a load force maximum. Analysis of the grip forces produced by the two subjects revealed that the grip forces underwent the same characteristic changes as the load forces. Thus, subjects were able to adjust grip forces in anticipation of arm movement-induced fluctuations in load force under different and novel load conditions. Adaptation to changing levels of gravity was also obvious when the vertical and horizontal movements were compared: grip forces depended heavily on movement direction during normal and hypergravity but not during microgravity. The predictive coupling of grip force and load force was observed even during transitions between gravity levels, indicating rapid adaptation to changing load conditions. To account for the striking preservation of the normal characteristics of grip force control, we suggest that a highly automatized, extremely flexible sensorimotor mechanism firmly implemented within the central nervous system can cope with even massive changes in the environmental conditions.

Adaptation, Physiological↗

PubMed1999

Grip forces exerted against stationary held objects during gravity changes.

In the present study, grip forces exerted against a stationary held object were recorded during parabolic flights. Such flight maneuvers induce changes of gravity with two periods of hypergravity, associated with a doubling of normal terrestrial gravity, and a 20 s period of microgravity. Accordingly, the object's weight changed from being twice as heavy as normally experienced and weightless. Grip-force recordings demonstrated that force control was seriously disturbed only during the first experience of hyper- and microgravity, with the grip forces being exceedingly high and yielding irregular fluctuations. Thereafter, however, grip force traces were smooth, the force level was scaled to the object's weight under normal and high-G conditions, and the grip force changed in parallel with the weight during the transitions between hyper- and microgravity. In addition, during weightlessness, when virtually no force was necessary to stabilize the object, a low force was established, which obviously represented a reasonable safety margin for preventing possible perturbations. Thus, all relevant aspects of grip-force control observed under normal gravity conditions were preserved during gravity changes induced by parabolic flights. Hence, grip-force control mechanisms were able to cope with hyper- and microgravity, either by incorporating relevant receptor signals, such as those originating from cutaneous mechanoreceptors, or by adequately including perceived gravity signals into control programs. However, the adaptation to the uncommon gravity conditions was not complete following the first experience; finer tuning of the control system to both hyper- and microgravity continued over the measurement interval, presumably with a longer observation period being necessary before a stable performance can be reached.

Adult↗

PubMed1999

Effects of unilateral brain damage on grip selection, coordination, and kinematics of ipsilesional prehension.

To determine whether the left and right hemispheres play specific roles in goal-directed movements, prehension with the ipsilesional hand was tested in patients with unilateral brain damage. The task required that subjects rotate the hand while reaching for a bar that was presented in different orientations in the frontal plane, thus making high demands on visuospatial processing. The grasped bar had to be put into a hole: under one task condition the placement of the bar was specified, while under another it was not. The constrained task required that the subject anticipate the placing action when planning the initial prehensile movement. Grip selection, reaction times, kinematics of the transport movement, and coordination of hand rotation during transport were assessed in ipsilesional movements of 22 patients with either left or right brain damage (LBD and RBD) and in control subjects. Patients in both groups exhibited performance deficits; however, impairment characteristics differed profoundly between the groups. RBD patients showed prolonged reaction time and degraded kinematics in the unconstrained task, whereas LBD patients performed relatively well when only the orientation of the bar varied, but slowly and frequently incoordinated when the subsequent action was specified. Our findings emphasize the dominant role of the right hemisphere in processing visuospatial aspects of goal-directed movements, whereas the left hemisphere subserves non-spatial aspects of preplanning under increased task demands. Correlations of the patient's performance with results from clinical tests showed that neither deficits in visuospatial perception of RBD patients nor apraxia of LBD patients could account for the observed abnormalities in the use of the ipsilesional hand.

Adult↗

PubMed1999

Prehension with the ipsilesional hand after unilateral brain damage.

Sensorimotor deficits in the hand ipsilateral to a brain lesion have been reported in different motor tasks. We evaluated performance of the ipsilesional hand in 12 patients with either left (LBD) or right brain damage (RBD) by kinematic analysis in order to precisely characterize possible deficits in the two components of prehension (transport and grasp). Both patient groups exhibited performance deficits in the main kinematic parameters, e.g., reduced velocity of the transport component and prolonged movement time. However, while LBD patients showed a more general slowing, RBD patients prolonged in particular the last phase of the movement toward the object. We suggest that relevant visuospatial representations and the adequate mapping of motor processes may be impaired after RBD. In contrast, LBD caused a more unspecific disturbance pattern, supporting the view that the precise parameterization of motor programs is impaired. Maximum grip aperture was normal in both patient groups. However, since aperture could be biased by slowed movement, the notion that the grasp component was preserved remains speculative. The patient's ability to scale the maximum velocity of the transport component to adapt to changes in movement amplitude and to scale the maximum hand aperture of the grasp component to adapt to object size was preserved in both groups. Thus both hemispheres can have competence for this scaling mechanism.

Adult↗

PubMed1999

Comparative analysis of diadochokinetic movements.

Tests of diadochokinesia are an inherent part of a neurological examination. Various quantifying methods have been proposed to increase the objectivity, sensitivity, and reliability of such examinations. The methods used and analyses performed, however, differ substantially between tasks. We used a three-dimensional, ultrasound-based recording device to continuously record joint angles during three diadochokinetic movements, avoiding any external constraints of the movements. Alternate pronation and supination of the forearm, tapping with the whole hand and with the index finger in isolation were analyzed in a sample of 63 healthy control subjects. The most sensitive measure for capturing effects of gender, sex, and active hand was frequency. The right hand was faster than the left in all tasks, tapping performance declined with increasing age, and male subjects were faster than females in forearm diadochokinesia. Other measures that characterize speed of movement such as maximum angular velocities and accelerations did not yield comparable sensitivity in detecting the same statistical effects. However, angular velocity achieved the highest test-retest reliability for forearm diadochokinesia, while frequency was reproduced in the tapping tasks. Additional measures characterizing symmetry of the angular velocity profiles and intraindividual variability were shown to be largely independent of movement speed. Examples in neurological patients showed that the data define a valuable standard against which pathological performance can be precisely evaluated. In addition, the different measures captured dissociable aspects of motor performance that may further help to characterize the deficit and adjust therapy.

Adult↗

PubMed1996

Ideomotor apraxia and cerebral dominance for motor control.

Ideomotor apraxia is a symptom of left hemisphere damage. Patients with ideomotor apraxia commit errors when imitating movements with their left, non-paralyzed hand. This has been taken as evidence for a motor dominance of the left hemisphere. It has been hypothesized that the left hemisphere is dominant for internal preprogramming of skilled movements of either hand. We investigated the kinematics of movement trajectories of imitation of meaningless gestures. Group analysis confirmed that hesitant, feedback-controlled movement prevail in patients with apraxia, but analysis of single cases revealed the existence of kinematically normal movements leading to apractic errors. Enhanced reliance on feedback-control appears to be a compensatory strategy rather than the source of apractic errors. In a second study we explored the alternative hypothesis that patients with apraxia lack a general concept of the human body which is necessary to mediate the translation of a target position seen on the model into a target position on the patient's body. Imitation of movements was examined on oneself and on a mannikin. Patients with apraxia who made errors when imitating on themselves committed errors also when imitating on the mannikin. Taken together, both studies support the view that the source of errors in the imitation of gestures is to be sought at a conceptual level. This casts doubts on the alleged dominance of the left hemisphere for motor control.

Apraxias↗