Biomedical subjects

J Konczak

Publications and source records attributed to J Konczak.

At least 19 recordsLinked to original sources

PubMed2005

The effect of subthalamic nucleus stimulation on kinaesthesia in Parkinson's disease.

BACKGROUND: Parkinson's disease is accompanied by deficits in passive motion and limb position sense. OBJECTIVE: To investigate whether deep brain stimulation of the subthalamic nucleus (STN-DBS) reverses these proprioceptive deficits. METHODS AND RESULTS: A passive movement task was applied to nine patients with Parkinson's disease and bilateral chronic STN-DBS and to seven controls. Thresholds for 75% correct responses were 0.9 degrees for controls, 2.5 degrees for Parkinson's disease patients when stimulation was OFF, and 2.0 degrees when stimulation was ON. CONCLUSIONS: STN-DBS improves kinaesthesic deficits in Parkinson's disease, but does not lead to a full recovery of proprioceptive function.

Adult↗

PubMed2001

The effect of the Ebbinghaus illusion on grasping behaviour of children.

Within the context of the Ebbinghaus illusion, adults regularly misjudge the physical size of a centre disc, yet scale their hand aperture according to its actual size. Separate visual pathways for perception and action are assumed to account for this finding. The dorsal visual stream is said to elaborate on egocentric (visuomotor), while the ventral stream is involved in allocentric transformations (object recognition). This study examines the ontogenetic development of this dissociation between perception and action in 35 children between the ages of 5 and 12 years. We report four major results. First, when children judged object size without grasping the disc, their judgements were deceived by the illusion to the same extent as adults. However, when asked to estimate size and then to grasp the disc, young children's (5-7 years) perceptual judgements became unreliable, while adults were still reliably deceived by the illusion in 80% of their trials. Second, the younger the children, the more their aperture was affected by the illusional surround. Discs of the same size were grasped with a smaller aperture when surrounded by a small annulus, although they were perceived as being larger. Third, young children used the largest safety margin during grasping. Fourth, the reliance on visual feedback decreased with increasing age, which was documented by shorter movement times and earlier maximum hand opening during grasping in the older children (feedforward control). Our results indicate that grasping behaviour in children is subject to an interaction between ventral and dorsal processes. Both pathways seem not to be functionally segregated in early and middle childhood. The data are inconclusive about whether young children predominantly use a specific visual stream for either a perceptual or motor task. However, our data demonstrate that children were relying on both visual processing streams during perceptual as well as visuomotor tasks. We found that children used egocentric cues to make perceptual judgements, while their grasping gestures were not exclusively shaped by viewer-centred but also by object-centred information.

Aging↗

PubMed2001

Predicting children's overarm throw ball velocities from their developmental levels in throwing.

This study examined the movement process-product relationship from a developmental perspective. The authors used multiple regression to investigate the changing relationship between qualitative movement descriptions of the overarm throw and the throwing outcome, horizontal ball velocity. Seventeen girls and 22 boys were filmed longitudinally at ages 6, 7, 8, and 13 years. Their movements were assessed using Roberton's (Roberton & Halverson, 1984) developmental sequences for action of the humerus, forearm, trunk, stepping, and stride length. The sequences accounted for 69-85% (adjusted) of the total velocity variance each year. The components that best predicted ball velocity changed over time, although humerus or forearm action always accounted for considerable variance. Gender was a good predictor of ball velocity, but if the developmental descriptions were entered first in a stepwise regression, gender then explained no more than 2% additional variance.

Adolescent↗

PubMed2000

Predictive control of muscle responses to arm perturbations in cerebellar patients.

OBJECTIVES: To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. METHODS: Eight cerebellar patients and eight sex and age matched control subjects participated. Subjects held a handle that was rotated around the elbow joint. They were instructed to hold the forearm at 90 degrees flexion against a mechanical perturbation. Extensor torque (5 Nm) was applied for 140 ms (pulse), or for 1400 ms (step) through an external motor. Motor responses were tested under two different conditions of anticipatory information. In the expected condition, subjects anticipated and received a pulse. Under the unexpected condition, subjects expected steps, but received unexpected pulses. Biceps and triceps EMG as well as angular kinematics were compared between expected and unexpected pulse perturbations to quantify possible effects of prediction. RESULTS: In all healthy subjects, the degree of overshoot in the return flexion movement was significantly less in expected pulse perturbations compared with unexpected trials. The degree of amplitude reduction was significantly smaller in the patient group than in the control group (22.8% v 40.0%). During the expected trials, latency of peak triceps activity was on average 20% shorter in the control group, but 4% larger in the cerebellar patients. CONCLUSIONS: In the expected condition, controls achieved a significant reduction in angular amplitude by generating triceps activity earlier, whereas the ability to use prediction for adjusting early antagonist responses after limb perturbation was impaired in cerebellar patients.

Adolescent↗

PubMed2000

Effect of prolonged neck muscle vibration on lateral head tilt in severe spasmodic torticollis.

UNLABELLED: Short term vibration of the dorsal neck muscles (10-35 s) is known to induce involuntary movements of the head in patients with spasmodic torticollis. To investigate whether neck muscle vibration might serve as a therapeutic tool when applied for a longer time interval, we compared a vibration interval of 5 seconds with a 15 minute interval in a patient with spasmodic torticollis with an extreme head tilt to the right shoulder. Head position was recorded with a two camera optoelectronic motion analyzer in six different test conditions. Vibration regularly induced a rapid change of head position that was markedly closer to a normal, upright posture. After 5 seconds of vibration, head position very quickly returned to the initial position within seconds. During the 15 minute interval, head position remained elevated. After terminating vibration in this condition, the corrected head position remained stable at first and then decreased slowly within minutes to the initial tilted position. CONCLUSIONS: (1) In this patient, muscle vibration was the specific sensory input that induced lengthening of the dystonic neck muscles. Neither haptic stimulation nor transcutaneous electrical stimulation had more than a marginal effect. (2) The marked difference in the change of head position after short and prolonged stimulation supports the hypothesis that spasmodic torticollis might result from a disturbance of the central processing of the afferent input conveying head position information-at least in those patients who are sensitive to sensory stimulation in the neck region. (3) Long term neck muscle vibration may provide a convenient non-invasive method for treating spasmodic torticollis at the central level by influencing the neural control of head on trunk position.

Female↗

PubMed1999

Do patients with neglect show abnormal hand velocity profiles during tactile exploration of peripersonal space?

It has been suggested that the movement impairments experienced by patients with neglect are not restricted to spatial disorders, but also affect higher-order kinematics (velocity and acceleration) to the extent that movements towards the neglected side are slower than movements away from it. In a recent study, we could not confirm this hypothesis, but found that patients with unilateral neglect exhibited no distinct direction-specific deficits in hand velocity when performing goal-directed reaching movements. Here we investigated whether neglect patients might reveal direction-specific deficits during exploratory hand movements. Six patients with left-sided neglect and six age-matched healthy control subjects scanned with their right hands the surface of a large table searching for a (non-existent) tactile target. Movements were performed in darkness. Time-position data of the hand were recorded with an optoelectronic camera system. Median activity of the patients' exploratory hand movements was shifted to the right (Karnath and Perenin 1998). Hand trajectories were partitioned into sections of leftward/rightward or, along the sagittal plane, into sections of near/far movements. For each movement section average and peak velocities were computed. The patients' hand movements were bradykinetic when compared with the control group. However, we found no evidence that average or peak velocities of leftward intervals were systematically lower than during rightward motion. Direction-specific deficits in velocity were also not observed for movements to and away from the body (sagittal plane). In conclusion, we found evidence for general bradykinesia in neglect patients but not for a direction-specific deficit in the control of hand velocity during exploratory hand movements.

Aged↗

PubMed1999

A developmental approach to visually-guided reaching in artificial systems.

The aim of the present paper is to propose that the adoption of a framework of biological development is suitable for the construction of artificial systems. We will argue that a developmental approach does provide unique insights on how to build highly complex and adaptable artificial systems. To illustrate our point, we will use as an example the acquisition of goal-directed reaching. In the initial part of the paper we will outline (a) how mechanisms of biological development can be adapted to the artificial world, and (b) how this artificial development differs from traditional engineering approaches to robotics. An experiment performed on an artificial system initially controlled by motor reflexes is presented, showing the acquisition of visuo-motor maps for ballistic control of reaching without explicit knowledge of the system's kinematic parameters.

Journal Article↗

PubMed1999

Identification of time-varying stiffness, damping, and equilibrium position in human forearm movements.

Knowledge of how stiffness, damping, and the equilibrium position of specific limbs change during voluntary motion is important for understanding basic strategies of neuromotor control. Presented here is an algorithm for identifying time-dependent changes in joint stiffness, damping, and equilibrium position of the human forearm. The procedure requires data from only a single trial. The method relies neither on an analysis of the resonant frequency of the arm nor on the presence of an external bias force. Its validity was tested with a simulated forward model of the human forearm. Using the parameter estimations as forward model input, the angular kinematics (model output) were reconstructed and compared to the empirically measured data. Identification of mechanical impedance is based on a least-squares solution of the model equation. As a regularization technique and to improve the temporal resolution of the identification process, a moving temporal window with a variable width was imposed. The method's performance was tested by (a) identifying a priori known hypothetical time-series of stiffness, damping, and equilibrium position, and (b) determining impedance parameters from recorded single-joint forearm movements during a hold and a goal-directed movement task. The method reliably reconstructed the original angular kinematics of the artificial and human data with an average positional error of less than 0.05 rad for movement amplitudes of up to 0.9 rad, and did not yield hypermetric trajectories like previous procedures not accounting for damping.

Acceleration↗

PubMed1998

Interaction of finger representation in the human first somatosensory cortex: a neuromagnetic study.

Neuromagnetic responses to separate tactile stimulation of digits I, II and V and simultaneous stimulation of digit pairs II and I, and II and V, were recorded in six healthy adult subjects using a 122-channel whole-head neuromagnetometer in order to investigate functional overlap of finger representations in primary somatosensory cortex (SI). Evoked responses to single digit stimulation were explained by time-varying equivalent current dipoles (ECDs) located in SI. These ECDs were then used to explain responses to stimulation of digit pairs. A cortical interaction ratio (IR) was defined as the vector sum of peak source amplitudes to separate stimulations of two fingers divided by the vector sum of source amplitudes to simultaneous stimulation of the two digits. Mean IR was significantly higher (P<0.05; Wilcoxon test) for digit pair II + I (1.69+/- 0.15) compared to digit pair II + V (1.14+/- 0.12). These results indicate that there is an overlap of finger representations in human SI which differs between anatomically adjacent and non-adjacent digit pairs.

Adult↗

PubMed1998

Kinematics of goal-directed arm movements in neglect: control of hand velocity.

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.

Adolescent↗

PubMed1998

Coordination of multi-joint arm movements in cerebellar ataxia: analysis of hand and angular kinematics.

Kinematic abnormalities of fast multijoint movements in cerebellar ataxia include abnormally increased curvature of hand trajectories and an increased hand path and are thought to originate from an impairment in generating appropriate levels of muscle torques to support normal coordination between shoulder and elbow joints. Such a mechanism predicts that kinematic abnormalities are pronounced when fast movements are performed and large muscular torques are required. Experimental evidence that systematically explores the effects of increasing movement velocities on movement kinematics in cerebellar multijoint movements is limited and to some extent contradictory. We, therefore, investigated angular and hand kinematics of natural multijoint pointing movements in patients with cerebellar degenerative disorders and healthy controls. Subjects performed self-paced vertical pointing movements with their right arms at three different target velocities. Limb movements were recorded in three-dimensional space using a two-camera infrared tracking system. Differences between patients and healthy subjects were most prominent when the subjects performed fast movements. Peak hand acceleration and deceleration were similar to normals during slow and moderate velocity movements but were smaller for fast movements. While altering movement velocities had little or no effect on the length of the hand path and angular motion of elbow and shoulder joints in normal subjects, the patients exhibited overshooting motions (hypermetria) of the hand and at both joints as movement velocity increased. Hypermetria at one joint always accompanied hypermetria at the neighboring joint. Peak elbow angular deceleration was markedly delayed in patients compared with normals. Other temporal movement variables such as the relative timing of shoulder and elbow joint motion onsets were normal in patients. Kinematic abnormalities of multijoint arm movements in cerebellar ataxia include hypermetria at both the elbow and the shoulder joint and, as a consequence, irregular and enlarged paths of the hand, and they are marked with fast but not with slow movements. Our findings suggest that kinematic movement abnormalities that characterize cerebellar limb ataxia are related to an impairment in scaling movement variables such as joint acceleration and deceleration normally with movement speed. Most likely, increased hand paths and decomposition of movement during slow movements, as described earlier, result from compensatory mechanisms the patients may employ if maximum movement accuracy is required.

Adult↗

PubMed1998

Multijoint arm movements in cerebellar ataxia: abnormal control of movement dynamics.

In cerebellar ataxia, kinematic aberrations of multijoint movements are thought to originate from deficiencies in generating muscular torques that are adequate to control the mechanical consequences of dynamic interaction forces. At this point the exact mechanisms that lead to an abnormal control of interaction torques are not known. In principle, the generation of inadequate muscular torques may result from an impairment in generating sufficient levels of torques or from an inaccurate assessment and prediction of the mechanical consequences of movements of one limb segment on adjacent joints. We sought to differentiate the relative contribution of these two mechanisms and, therefore, analyzed intersegmental dynamics of multijoint pointing movements in healthy subjects and in patients with cerebellar degeneration. Unrestrained vertical arm movements were performed at three different target movement velocities and recorded using an optoelectronic tracking system. An inverse dynamics approach was employed to compute net joint torques, muscular torques, dynamic interaction torques and gravitational torques acting at the elbow and shoulder joint. In both groups, peak dynamic interaction forces and peak muscular forces were largest during fast movements. In contrast to normal subjects, patients produced hypermetric movements when executing fast movements. Hypermetric movements were associated with smaller peak muscular torques and smaller rates of torque change at elbow and shoulder joints. The patients' deficit in generating appropriate levels of muscular force were prominent during two different phases of the pointing movement. Peak muscular forces at the elbow were reduced during the initial phase of the movement when simultaneous shoulder joint flexion generated an extensor influence upon the elbow joint. When attempting to terminate the movement, gravitational and dynamic interaction forces caused overshooting extension at the elbow joint. In normal subjects, muscular torque patterns at shoulder and elbow joint were synchronized in that peak flexor and extensor muscular torques occurred simultaneously at both joints. This temporal pattern of muscular torque generation at shoulder and elbow joint was preserved in patients. Our data suggest that an impairment in generating sufficient levels of phasic muscular torques significantly contributes to the patients' difficulties in controlling the mechanical consequences of dynamic interaction forces during multijoint movements.

Adult↗

PubMed1997

The temporal control of repetitive articulatory movements in Parkinson's disease.

Recent clinical data indicate that internal cueing mechanisms required for the triggering of movement sequences are impaired in Parkinson's disease (PD). Nevertheless, most PD subjects produce maximal syllable repetition rates similar to those observed in healthy control individuals during oral diadochokinesis tasks. There is some evidence that tremor oscillations may pace repetitive movements in Parkinsonians giving rise to hastening phenomena. Conceivably, the performance of PD patients in syllable repetition tasks thus reflects a specific timing deficit, i.e., articulatory hastening. It is the aim of the present study to investigate the contribution of speech hastening to oral diadochokinesis in the presence of internal and external cues. By means of an optoelectric movement analysis system, the displacements of the lips during repetitions of the syllable /pa/ were recorded in two akinetic-rigid PD individuals. Subjects were asked to synchronize labial diadochokinesis to sequences of periodic acoustic stimuli (2.5-6 Hz). One of the PD patients showed speech hastening, i.e., he produced repetitions of 8 to 9 Hz whenever stimulus frequencies exceeded 4 Hz. The other Parkinsonian adequately matched the stimulus frequencies required. However, she achieved a higher diadochokinesis rate in the matching task than under the instruction to repeat "as fast as possible." Thus, the presence of an external cue improved performance. In conclusion, our data indicate two deficits of the temporal control of repetitive articulatory gestures in PD: speech hastening and impaired self-paced sequencing. These two pathomechanisms may allow to reconcile the controversial findings on oral diadochokinesis in PD reported so far.

Female↗

PubMed1997

Control of repetitive lip and finger movements in Parkinson's disease: influence of external timing signals and simultaneous execution on motor performance.

This study addresses the question of whether external timing signals and/or simultaneous rhythmic movements of other limbs can alleviate sequencing motor deficits associated with Parkinson's disease (PD). Subjects performed rhythmic lip and finger movements simultaneously or in isolation. In addition, they had to self-pace their movements or match them to an external signal. Our results are summarized as follows: (1) Seven of 12 patients had adequate mean repetition rates; that is, they fulfilled the task requirements on a global scale. The remaining five patients had various degrees of hastened responses and were not fully able to synchronize their movements to an external pacing signal. (b) PD patients exhibited hypometria in their finger tapping, but not in their lip movements. Their movements were not abnormally slowed, but peak velocity was appropriately scaled, even to reduced movement amplitudes. (c) Mean repetition rates, stability of frequency response, and kinematics did not differ between conditions of external and internal stimulation within the PD group, but were different form the control group performance. (d) Kinematic measures were not improved during dual-task execution. PD patients were not able to maintain a 1:1 rhythm between effectors. The incidence of hastening increased during simultaneous motor execution. We conclude that the use of external pacing signals might aid movement initiation of PD patients, but does not improve their temporal or spatial coordination when generating repetitive movements. Simultaneous execution does not necessarily enhance motor performance, but might actually have detrimental effects in patients prone to hastening.

Aged↗

PubMed1997

The development of goal-directed reaching in infants. II. Learning to produce task-adequate patterns of joint torque.

Nine young infants were followed longitudinally from 4 to 15 months of age. They performed multi-joint reaching movements to a stationary target presented at shoulder height. Time-position data of the hand, shoulder, and elbow were collected using an optoelectronic measurement system. In addition, we recorded electromyographic activity (EMG) from arm extensors and flexors. This paper documents how control problems of proximal torque generation may account for the segmented hand paths seen during early reaching. Our analysis revealed the following results: first, muscular impulse (integral of torque) increased significantly between the ages of 20 (reaching onset) and 64 weeks. That is, as infants got older they produced higher levels of mean muscular flexor torque during reaching. Data were normalized by body weight and movement time, so differences are not explained by anthropometric changes or systematic variations in movement time. Second, while adults produced solely flexor muscle torque to accomplish the task, infants generated flexor and extensor muscle torque at shoulder and elbow throughout a reach. At reaching onset more than half of the trials revealed this latter kinetic profile. Its frequency declined systematically as infants got older. Third, we examined the pattern of muscle coordination in those trials that exhibited elbow extensor muscle torque. We found that during elbow extension coactivation of flexor and extensor muscles was the predominant pattern in 67% of the trials. This pattern was notably absent in comparable adult reaching movements. Fourth, fluctuations in force generation, as measured by the rate of change of total torque (NET) and muscular torque (MUS), were more frequent in early reaching (20-28 weeks) than in the older cohort (52-64 weeks), indicating that muscular torque production became increasingly smoother and task-efficient. Our data demonstrate that young infants have problems in generating smooth profiles of proximal joint torques. One possible reason for this imprecision in infant force control is their inexperience in predicting the magnitude and direction of external forces. That infants learned to consider external forces is documented by their increasing reliance on these forces when performing voluntary elbow extensions. The patterns of muscle coordination underlying active elbow extensions were basically the same as during the prereaching phase, indicating that the formation of functional synergies is based on a basal repertoire of innervation patterns already observable in very early, spontaneous movements.

Child Development↗

PubMed1997

The development toward stereotypic arm kinematics during reaching in the first 3 years of life.

We recorded reaching movements from nine infants longitudinally from the onset of reaching (5th postnatal month) up to the age of 3 years. Here we analyze hand and proximal joint trajectories and examine the emerging temporal coordination between arm segments. The present investigation seeks (a) to determine when infants acquire consistent, adult-like patterns of multijoint coordination within that 3-year period, and (b) to relate their hand trajectory formation to underlying patterns of proximal joint motion (shoulder, elbow). Our results show: First, most kinematic parameters do not assume adult-like levels before the age of 2 years. At this time, 75% of the trials reveal a single peaked velocity profile of the hand. Between the 2nd and 3rd year of life, "improvements" of hand- or joint-related movement units are only marginal. Second, infant motor systems strive to obtain velocity patterns with as few force reversals as possible (uni- or bimodal) at all three limb segments. Third, the formation of a consistent interjoint synergy between shoulder and elbow motion is not achieved within the 1st year of life. Stable patterns of temporal coordination across arm segments begin to emerge at 12-15 months of age and continue to develop up to the 3rd year. In summary, the development toward adult forms of multijoint coordination in goal-directed reaching requires more time than previously assumed. Although infants reliably grasp for objects within their workspace 3-4 months after the onset of reaching, stereotypic kinematic motor patterns are not expressed before the 2nd year of life.

Aging↗

PubMed1997

Kinematics of goal-directed arm movements in neglect: control of hand in space.

The present study investigated unrestrained, three-dimensional arm movements during goal-directed pointing in five patients with clinically manifest neglect to targets positioned either in the center or the left and right hemispace. Five patients with unilateral right hemispheric lesions without neglect and six healthy subjects served as controls. All subjects were able to point to these targets. Terminal accuracy of pointing did not differ between the three groups along the horizontal, vertical and anterior-posterior axis. Subjects' hand trajectories did not reveal direction-specific deviations from a straightline hand path. Our data show that deviations in the trajectories toward the ipsilesional side are not characteristic for patients with spatial neglect. We argue that exploratory and goal-directed motor behavior might not share the same egocentric, body-centered reference frame. A spatial reference frame for exploratory behavior is disturbed in patients with neglect resulting in a failure to explore the contralesional part of space by eye or limb movements. Its failure does not induce a spatial bias in hand trajectory formation during goal-directed arm movements in peripersonal space. Such deviations of reaching or pointing rather seem to be characteristic for patients with optic ataxia.

Adolescent↗

PubMed1996

Functional training: muscle structure, function, and performance in older women.

Response to physical training at the cellular and whole muscle level has been established in older adults. However, the underlying molecular mechanism responsible for change has not been described nor have the relationships between change in muscle structure and functional performance been established. The purpose of this research study is to evaluate the changes of muscle ultrastructure, muscle strength, and whole body functional performance as a result of a functionally directed exercise program (stair climbing). Women (65-83 years old) selected either the control (no exercise; N = 6) or exercise (N = 7) group. The 1-year functionally based exercise program was both aerobic (75% heart rate reserve) and resistive (weighted stair climbing). Muscle ultrastructure, determined by quantitative morphometry of the vastus lateralis tissue, and maximal step-height achieved by each subject were related to isokinetic strength and muscle morphology. Changes in myofibrillar area accounted for 48% of the variance in muscle strength changes. Change in muscle contractile protein was the underlying basis for change in thigh strength which, in turn, was the basis for functional performance. These data provide evidence that, in older women, a mild functionally based training program results in improved muscle structure and performance of the lower body.

Aged↗