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Converting left-handers to their non-dominant right hand was previously widespread, particularly for handwriting. The present study aimed to explore the extent to which adult, converted left-handers can learn writing with their dominant left hand during a 2-year training program. Eleven converted left-handers participated in the training. Handwriting kinematics were assessed at regular intervals (seven sessions) and compared to those of 11 innate left-handed controls matched for age, gender, and overall handedness score for basic (Finger, Wrist, Circle) and complex (Sentence, Copy) handwriting tasks. Regarding basic tasks in the training group, we found rapid increases in left and right-hand frequency and no significant differences between both hands at any time point, indicating successful hand transfer. After 24 months, training participants significantly surpassed controls for writing frequency in basic tasks with their left hand. For complex tasks, we identified significant increases in the training groups' left-hand writing frequency and duration between the first and last session. While training participants' left-hand writing remained significantly slower than their right-hand writing, statistics confirmed final differences between hands only for the duration of the Sentence task. Importantly, left-hand writing in the training group was characterized by lower frequency, lower automaticity, and prolonged duration after 24 months compared to innate left-handers. With training participants' left-hand writing skills significantly increasing for complex tasks and no final statistically significant differences between hands for frequency and automaticity, the program was considered effective. Nevertheless, within 2 years, training participants did not reach innate left-handers handwriting proficiency for complex tasks. Underlying reasons may be various, such as a non-optimal training program, a sensitive period for learning to write, irreversible neural changes during conversion in childhood, age-related decline of motor learning capacity, or retrograde interference between right- and left-hand writing., (© 2023. The Author(s).)

Objective: To determine factors characterizing the differences in fine motor performance between stroke patients and controls. To confirm the relevance of the factors by analyzing their predictive power with regard to the Jebsen Taylor Hand Function Test (JTHFT), a common clinical test of fine motor control., Methods: Twenty-two people with slight paresis in an early chronic phase following stroke and twenty-two healthy controls were examined. Performance on the JTHFT, Nine-Hole Peg Test and 2-point discrimination was evaluated. To analyze object manipulation skills, grip forces and temporal measures were examined during (1) lifting actions with variations of weight and surface (2) cyclic movements (3) predictive/reactive catching tasks. Three other aspects of force control included (4) visuomotor tracking (5) fast force changes and (6) grip strength., Results: Based on 9 parameters which significantly distinguished fine motor performance in the two groups, we identified three principal components (factors): grip force scaling, motor coordination and speed of movement. The three factors are shown to predict JTHFT scores via linear regression (R 2 =0.687, p<0.001)., Conclusions: We revealed a factor structure behind fine motor impairments following stroke and showed that it explains JTHFT results to a large extend., Significance: This result can serve as a basis for improving diagnostics and enabling more targeted therapy., (Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

One way to foster the understanding of the impressively skilled fine motor control of human object manipulation is to investigate the rules of the underlying fundamental mechanisms. Examining the action of grasping and lifting objects of various characteristics reveals that one vital step to handle objects in a skilled and fluent way is to predict their properties and plan motor actions accordingly. A large number of behavioral studies have extracted the factors on which we rely when we interact with objects in an anticipatory mode of action. At the same time, considerable effort was taken to elucidate the neuroanatomical areas and networks involved and crucial for anticipatory behavior by conducting functional imaging and stimulation studies and examining the deficits of patients with localized brain damage. This chapter gives an overview of these studies and tries to reconcile their findings, in order to provide an insight into the basic principles of anticipatory motor control and their underlying neural substrates.

Objective: We introduced a new visually controlled tracking task that can be assessed on a handheld device in shift workers to evaluate time-of-day dependent modulations in visuomotor performance., Background: Tracking tasks have been used to predict performance fluctuations depending on time of day mainly under laboratory conditions. One challenge to an extended use at the actual working site is the complex and fixed test setup consisting of a test unit, a monitor, and a manipulation object, such as a joystick., Method: Participants followed an unpredictably moving target on the screen of a handheld device with an attachable stylus. A total of 11 shift workers (age range: 20-59, mean: 33.64, standard deviation: 10.56) were tested in the morning, the evening, and the night shift in 2-hr intervals with the tracking task and indicated their fatigue levels on visual analogue scales. We evaluated tracking precision by calculating the mean spatial deviation from the target for each session., Results: Tracking precision was significantly influenced by the interaction between shift and session, suggesting a clear time-of-day effect of visuomotor performance under real-life conditions. Tracking performance declined during early-morning hours whereas fatigue ratings increased., Conclusion: These findings suggest that our setup is suitable to detect time-of-day dependent performance changes in visually guided tracking., Application: Our task could be used to evaluate fluctuations in visuomotor coordination, a skill that is decisive in various production steps at the actual working place to assess productivity.

Impairment of patients with cerebellar disease in prehension is well recognized. So far specific localizations within the human cerebellum associated with the impairment have rarely been assessed. To address this question we performed voxel-based lesion symptom mapping (VLSM) in patients with chronic focal cerebellar lesions in relation to specific deficits in prehensile movements. Patients with stroke within the posterior inferior cerebellar artery territory (n = 13) or the superior cerebellar artery (SCA) territory (n = 7) and corresponding control subjects were included in the study. Participants reached out, grasped, and lifted an object with either the left or right hand and with fast or normal movement speed. Both kinematic and grip-force parameters were recorded. Magnetic resonance imaging anatomical scans of the cerebellum were acquired, and lesions were marked as regions of interest. For VLSM analysis, a nonparametric test (Brunner-Munzel) was applied. Cerebellar patients showed clear abnormalities in hand transport (impaired movement speed and straightness) and, to a lesser degree, in hand shaping (increased finger touch latencies) while grip function was preserved. Deficits were most prominent in patients with SCA lesions and for ipsilesional, fast movements. Disorders in hand transport may be more difficult to compensate than deficits in hand shaping and grip-force control in chronic focal lesions of the cerebellum because of higher demands on predictive control of interaction torques. Lesions of the superior cerebellar cortex (lobules IV, V, VI) were associated with slower hand transport, whereas lesions of both superior (lobules VI, V, VI) and inferior cerebellar cortex (lobules VII, VIII) were associated with impaired movement straightness. These findings show that both the superior and inferior hand representations within the cerebellum contribute to hand transport during prehensile movements; however, they may have a different functional role.

Callosal disconnection can reveal asymmetrical contributions of the two brain hemispheres to praxis. In this paper, we revisit a study of a patient with callosal disconnection (Goldenberg et al., 2001, Neuropsychologia, 39:1432-1443), who perfectly imitated meaningless gestures when imitation was controlled only by the left hemisphere, but was severely impaired when the right hemisphere was in charge of motor control. We decomposed the gestures into a set of geometric variables that were to be reproduced, such as the orientation of the hand and the position of contact between the hand and the face. Whereas orientation of the hand in extrinsic coordinates was replicated correctly by both hemispheres, only the left hemisphere reproduced correctly the position of contact between the hand and the face. This goal-dissociation as well as several partial perseveration errors speak against the hypothesis of a direct route from perception to motor replication of gestures, as interruption of a direct route would probably impair all the features of the gesture. We speculate that incorrect coordination between the reproductions of multiple goals may be the core deficit underlying callosal apraxia., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Objective: To evaluate the use of a modified pen grip and subsequent handwriting training in patients with writer's cramp (WC)., Design: Handwriting performance with normal and modified pen grip was examined once in healthy controls and repeatedly in patients with WC (2 baseline tests before training, directly after training, after a 3-month follow-up)., Setting: Ambulatory care for motor writing disorders., Participants: Patients with WC (n=26) and healthy controls (n=14)., Intervention: Seven sessions of handwriting training with various motor exercises were conducted by an occupational therapist. During training, the patients always used a modified pen grip (stabilized between index and middle finger)., Main Outcome Measures: Writing frequency and fluency, grip force on the pen, writing pressure, Fahn dystonia scale, visual analog scales for impairment and pain., Results: Patients with WC showed increased writing pressure and grip force before training. Using the modified pen grip caused in both patients with WC and controls a decrease in pressure and grip force. Handwriting training resulted in a further improvement of both parameters in patients with WC. Grip force reduction remained stable over follow-up., Conclusions: Results suggest that patients with WC benefit from the use of the modified pen grip in combination with handwriting training.

Study Design: Pre-post, single-group., Introduction: Writer's cramp (WC) is a focal dystonia causing impairments in daily life. Behavioral treatment approaches have been shown to improve handwriting performance, though outcomes remain sub-optimal., Purpose of the Study: To examine the effects of the handwriting training and auditory grip force feedback in seven patients with WC., Methods: Handwriting performance was examined before and after treatment. Writing frequency, fluency, and pressure were recorded with a digitizing tablet and grip forces during handwriting were recorded. Subjective writing performance and pain were rated on visual analog scales., Results: The treatment resulted in significant reductions in writing pressure and pain, while writing performance was significantly improved., Conclusions: Patients in this study with WC, who exhibit grip force and pressure problems, benefit from feedback-supported handwriting training.

Background: Although feed-forward mechanisms of grip force control are a prerequisite for skilled object manipulation, somatosensory feedback is essential to acquire, maintain, and adapt these mechanisms., Objective: Individuals with complete peripheral deafferentation provide the unique opportunity to study the function of the motor system deprived of somatosensory feedback., Methods: Two individuals (GL and IW) with complete chronic deafferentation of the trunk and limbs were tested during cyclic vertical movements of a hand-held object. Such movements induce oscillating loads that are typically anticipated by parallel modulations of the grip force. Load magnitude was altered by varying either the movement frequency or object weight., Results: GL and IW employed excessive grip forces probably reflecting a compensatory mechanism. Despite this overall force increase, both deafferented participants adjusted their grip force level according to the load magnitude, indicating preserved scaling of the background grip force to physical demands. The dynamic modulation of the grip force with the load force was largely absent in GL, whereas in IW only slower movements were clearly affected., Conclusions: The authors hypothesize that the deafferented patients may have utilized visual and vestibular cues and/or an efferent copy of the motor command of the arm movement to scale the grip force level. Severely impaired grip force-load coupling in GL suggests that sensory information is important for maintaining a precise internal model of dynamic grip force control. However, comparably better performance in IW argues for the possibility that alternative cues can be used to trigger a residual internal model.

Impaired hand function is a frequent finding in movement disorders. The skilled control of prehensile finger forces is an essential feature of tool use in daily life. In healthy subjects, grip force is precisely adjusted to the mechanical object properties, such as weight and surface friction. Grip force is accurately scaled to be only a small amount higher than the minimum necessary to prevent a hand-held object from slipping. When an object is lifted and moved around in space, grip force is modulated in parallel with the movement-induced fluctuations in load. The absence of a temporal delay between grip and load force profiles implies that the central nervous system is able to predict the load variations before the intended manipulation. Sensory information is used to adjust the level of applied finger forces efficiently to the requirements of the mechanical object properties and the task at hand. The characteristics of impaired finger force control include inefficient grip force scaling and imprecision of the temporal coupling between grip and load force profiles. Here, we review the characteristics of deficient grip force behavior in movement disorders, e.g. Parkinson's disease, task-specific dystonia, Gille de la Tourette's syndrome and cerebellar disease. Grip force analysis is a highly sensitive method to document even subtle impairments of finger force control and may be used both as a diagnostic tool and for the objective evaluation of treatment in neurological movement disorders.

Impairments of the ipsilesional hand after brain damage have been reported in goal-directed motor acts and in pantomimes; the relationship between both movement conditions is largely unknown. In the presented study, pantomimed and actual prehension was examined in 29 stroke patients with left brain damage (LBD) or right brain damage (RBD) as well as in 21 control subjects. Kinematic analyses revealed various performance differences between the conditions of movement execution and the subject groups. The differences depended on the hand tested and on the side of the brain lesion. During actual prehension deviations from normal performance were obvious in the peak velocity of the transport component of the movement, which was reduced in RBD patients, and in the duration of the final adjustment phase, which was prolonged in both patient groups. Pantomime changed various features of movement execution. The transport component was particularly altered in the groups performing with the right hand. Hand aperture was significantly smaller during pantomime than during actual movement execution in all groups. However, this effect was particularly obvious in LBD patients, in whom the hand aperture was even completely absent during many of their pantomimes. Actual movement execution immediately preceding the pantomimes did not change the characteristic features of pantomimes. Thus, the cerebral processes for actually executed and pantomimed motor acts differ. Actual movements seem to be governed by external affordances and constraints; whereas, pantomimes may represent a symbolic act. During prehension, differences in grip formation reveal most directly this dichotomy. We argue that the left hemisphere plays a special role in the generation of the symbolic act; a lesion may abolish grip formation and causes the clinical symptom of apraxia.

The control of prehensile finger forces is an essential feature of all skilled manual performance. The basic aspects of healthy grip force control have been well documented within the past two decades. In healthy subjects, grip force is accurately adjusted to the mechanical object properties such as weight, surface friction, and shape: when we move a hand-held object, grip force is modulated in parallel with movement-induced load fluctuations without an apparent temporal delay. At all phases of the movement, grip force is always slightly higher than the minimum necessary to prevent the object from slipping. The absence of a temporal delay between grip and load force profiles implies that the central nervous system is able to predict load variations precisely before the intended manipulation, and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the force level efficiently to the actual load requirements. Pathologic grip force control affects the efficiency of the forces produced and the predictive temporal coupling between grip and load force profiles. Here we demonstrate pathologic grip force control in various neurologic disorders. The analysis of grip force control is simple and highly sensitive for detecting healthy and pathologic motor behaviour. The examination of grip force control is well suited for an objective evaluation of therapy during sensorimotor rehabilitation of deficient hand function.

When subjects repetitively lift an object, the grip force they select is influenced by the mechanical object properties of the preceding lift. Similar effects on grip force scaling are observed whether the subsequent lift is performed with the same hand or the hand contralateral to the preceding lift. Here we demonstrate that passive vibration of the hand muscles involved in the generation of grip force in the interval between two blocks of lifting trials interferes with predictive grip force scaling. Following ten trials in which subjects lifted an object with constant mechanical properties with the dominant hand, muscle vibration was given to the first interosseus and adductor pollicis muscles of the dominant hand during a 10-min rest period. Compared with the last lift preceding vibration, peak rates of grip force increase and peak grip forces were scaled too high during the first lift following vibration whether the lift was made with the dominant or non-dominant hand. Subjects scaled grip force accurately to the object properties within three lifts following vibration. If subjects rested for 10 min after the first ten trials and received no vibration, then there was no significant difference in the peak grip force or its rate of increase between the last lift preceding rest and the first lift following it. We suggest that vibration impairs the memory processes responsible for predictive grip force scaling. Our data are consistent with the recent suggestion that these memory processes are neither specific for a certain motor action nor do they reflect internal representations of mechanical object properties.

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.

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.

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.

Accuracy of the final position and kinematics of movement were analysed during the imitation of meaningless gestures in patients with unilateral brain lesions who performed with the hand ipsilateral to the lesion and in control subjects. Controls imitated the gestures virtually without spatial errors. The kinematics of their movements was characterized by single-peaked and approximately bell-shaped velocity profiles of the transport phase combined with no or only minor corrective movements in the final phase. Patients with right brain damage (RBD) performed as well as control subjects with respect to both spatial accuracy of final hand-positions and kinematic parameters of the movement trajectories. Patients with left brain damage (LBD) committed spatial parapraxias and had a much higher frequency of kinematic abnormalities. However, there was no correlation between kinematic abnormalities and apraxic errors. There were kinematically abnormal movements which reached a correct final position as well as kinematically normal movements leading to apraxic errors. One possible explanation for the combined occurrence of kinematic abnormalities and parapraxias in LBD patients would be that they are independent sequels of left hemisphere lesions. An alternative account is that the associations and dissociations result from an interaction between one common basic deficit and strategies to cope with this deficit. The basic deficit may concern the mental representation of the target position. The LBD patients may react to the absence of an appropriate representation of the target by one of two alternative strategies; they may switch to a strategy of slowed, on-line controlled movements to find the required final position, or they may move their hand smoothly at normal speed to a roughly specified location without taking note of their deficiency. Depending on whether these strategies are successful or not they would lead to the observed associations and dissociations between kinematic abnormalities and spatial parapraxias.

Precise control of grip force and finger movement is a fundamental aspect of motor tasks in which an object is held and manipulated between the subject's fingers. A new device to measure motor performance which simultaneously records grip force and finger movement is described. The subject holds a small, compressible cylinder between thumb and index finger. The load opposing finger movements is controlled pneumatically and may be altered with computer software. Different types of loads (e.g., constant load, spring load) may be applied. In addition, reactions to perturbing stimuli (e.g., fast changes of load) may be measured. Construction principles and examples of tasks investigating different aspects of hand function are presented in the paper.