Manual asymmetries in reaching movement control. I: Study of right-handers

Interhemispheric imbalance and bradykinesia features in Parkinson's disease

In patients with Parkinson's disease, the connectivity between the two primary motor cortices may be altered. However, the correlation between asymmetries of abnormal interhemispheric connections and bradykinesia features has not been investigated. Furthermore, the potential effects of dopaminergic medications on this issue remain largely unclear. The aim of the present study is to investigate the interhemispheric connections in Parkinson's disease by transcranial magnetic stimulation and explore the potential relationship between interhemispheric inhibition and bradykinesia feature asymmetry in patients. Additionally, we examined the impact of dopaminergic therapy on neurophysiological and motor characteristics. Short- and long-latency interhemispheric inhibition was measured in 18 Parkinson's disease patients and 18 healthy controls, bilaterally. We also assessed the corticospinal and intracortical excitability of both primary motor cortices. We conducted an objective analysis of finger-tapping from both hands. Correlation analyses were performed to explore potential relationships among clinical, transcranial magnetic stimulation and kinematic data in patients. We found that short- and long-latency interhemispheric inhibition was reduced (less inhibition) from both hemispheres in patients than controls. Compared to controls, finger-tapping movements in patients were slower, more irregular, of smaller amplitudes and characterized by a progressive amplitude reduction during movement repetition (sequence effect). Among Parkinson's disease patients, the degree of short-latency interhemispheric inhibition imbalance towards the less affected primary motor cortex correlated with the global clinical motor scores, as well as with the sequence effect on the most affected hand. The greater the interhemispheric inhibition imbalance towards the less affected hemisphere (i.e. less inhibition from the less to the most affected primary motor cortex than that measured from the most to the less affected primary motor cortex), the more severe the bradykinesia in patients. In conclusion, the inhibitory connections between the two primary motor cortices in Parkinson's disease are reduced. The interhemispheric disinhibition of the primary motor cortex may have a role in the pathophysiology of specific bradykinesia features in patients, i.e. the sequence effect.

Enhanced efficiency in visually guided online motor control for actions redirected towards the body midline

Reaching objects in a dynamic environment requires fast online corrections that compensate for sudden object shifts or postural changes. Previous studies revealed the key role of visually monitoring the hand-to-target distance throughout action execution. In the current study, we investigate how sensorimotor asymmetries associated with space perception, brain lateralization and biomechanical constraints, affect the efficiency of online corrections. Participants performed reaching actions in virtual reality, where the virtual hand was progressively displaced from the real hand to trigger online corrections, for which it was possible to control the total amount of the redirection and the region of space in which the action unfolded. The efficiency of online corrections and the degree of awareness of the ensuing motor corrections were taken as assessment variables. Results revealed more efficient visuo-motor corrections for actions redirected towards, rather than away from the body midline. The effect is independent on the reaching hand and the hemispace of action, making explanations associated with laterality effects and biomechanical constraints improbable. The result cannot either be accounted for by the visual processing advantage in the straight-ahead region. An explanation may be found in the finer sensorimotor representations characterizing the frontal space proximal to body, where a preference for visual processing has been documented, and where high-value functional actions, like fine manipulative skills, typically take place. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Movement Kinematics and Interjoint Coordination Are Influenced by Target Location and Arm in 6-Year-Old Children

Rapid aiming movements are typically used to study upper limb motor control and development. Despite the large corpus of work in this area, few studies have examined kinematic manual asymmetries in children who have just started formal schooling and until now, none have characterized how children coordinate their joints to complete these movements (i.e., interjoint coordination). In the present study, manual asymmetries in kinematics and interjoint coordination in strongly right-handed 6-year-old children were investigated when reaching for ipsilateral and contralateral targets with their dominant right arm and the non-dominant left arm. Overall, manual asymmetries in interjoint coordination are apparent for both 6-year-old children and young adults, although young children completed the task by adopting a different strategy than adults. Also, control strategies employed by 6-year-old children were influenced by both the location of the target as well as the arm used to perform the task. Specifically, compared to all other conditions, children’s trajectories were more curved when performing contralateral movements with the non-dominant left arm, which were driven by smaller shoulder excursions combined with larger elbow excursions for this condition. Based on these results, we argue that the differences in interjoint coordination reflect the stage of development of 6-year-old children, the origin of which derives from maturational (e.g., hand dominance) and environmental factors (e.g., school-based experience).

Online corrective responses following target jump in altered gravitoinertial force field point to nested feedforward and feedback control

Studies on goal-directed arm movements have shown a close link between feedforward and feedback control in protocols where both planning and online control processes faced a similar type of perturbation, either mechanical or visual. This particular context might have facilitated the use of an adapted internal model by feedforward and feedback control. Here, we considered this link in a context where, after feedforward control was adapted through proprioception-based processes, feedback control was tested under visual perturbation. We analyzed the response of the reaching hand to target displacements following adaptation to an altered force field induced by rotating participants at constant velocity. Reaching corrections were assessed through variables related to the accuracy (lateral and longitudinal end point errors) and kinematics (movement time, peak velocity) of the corrective movements. The electromyographic activity of different arm muscles (pectoralis, posterior deltoid, biceps brachii, and triceps brachii) was analyzed. Statistical analyses revealed that accuracy and kinematics of corrective movements were strikingly alike between normal and altered gravitoinertial force fields. However, pectoralis and biceps muscle activities recorded during corrective movements were significantly modified to counteract the effect of rotation-induced Coriolis and centrifugal forces on the arm. Remarkably, feedback control was functional from the very first time participants encountered a target jump in the altered force field. Overall, the present results demonstrate that feedforward control enables immediate functional feedback control even when applied to distinct sensorimotor processes.NEW & NOTEWORTHY We investigated the link between feedforward and feedback control when applying a double-step perturbation (visual target jump) during reaching movements performed in modified gravitoinertial environments. Altogether, kinematics and EMG analyses showed that movement corrections were highly effective in the different force fields, suggesting that, although feedforward and feedback control were driven by different sensory inputs, feedback control was remarkably functional from the very first time participants encountered a target jump in the altered force field.

On the Neurocircuitry of Grasping: The influence of action intent on kinematic asymmetries in reach-to-grasp actions

Evidence from electrophysiology suggests that nonhuman primates produce reach-to-grasp movements based on their functional end goal rather than on the biomechanical requirements of the movement. However, the invasiveness of direct-electrical stimulation and single-neuron recording largely precludes analogous investigations in humans. In this review, we present behavioural evidence in the form of kinematic analyses suggesting that the cortical circuits responsible for reach-to-grasp actions in humans are organized in a similar fashion. Grasp-to-eat movements are produced with significantly smaller and more precise maximum grip apertures (MGAs) than are grasp-to-place movements directed toward the same objects, despite near identical mechanical requirements of the two subsequent (i.e., grasp-to-eat and grasp-to-place) movements. Furthermore, the fact that this distinction is limited to right-handed movements suggests that the system governing reach-to-grasp movements is asymmetric. We contend that this asymmetry may be responsible, at least in part, for the preponderance of right-hand dominance among the global population.

Kinematics of ventrally mediated grasp-to-eat actions: right-hand advantage is dependent on dorsal stream input

Studies have suggested a left-hemisphere specialization for visually guided grasp-to-eat actions by way of task-dependent kinematic asymmetries (i.e., smaller maximum grip apertures for right-handed grasp-to-eat movements than for right-handed grasp-to-place movements or left-handed movements of either type). It is unknown, however, whether this left-hemisphere/right-hand kinematic advantage is reliant on the dorsal "vision-for-action" visual stream. The present study investigates the kinematic differences between grasp-to-eat and grasp-to place actions performance during closed-loop (i.e., dorsally mediated) and open-loop delay (i.e., ventrally mediated) conditions. Twenty-one right-handed adult participants were asked to reach to grasp small food items to (1) eat them, or (2) place them in a container below the mouth. Grasps were performed in both closed-loop and open-loop delay conditions, in separate sessions. We show that participants displayed the right-hand grasp-to-eat kinematic advantage in the closed-loop condition, but not in the open-loop delay condition. As no task-dependent kinematic differences were found in ventrally mediated grasps, we posit that the left-hemisphere/right-hand advantage is dependent on dorsal stream processing.

Leftward Deviation and Asymmetric Speed of Egocentric Judgment between Left and Right Visual Fields

The egocentric reference frame is essential for body orientation and spatial localization of external objects. Recent neuroimaging and lesion studies have revealed that the right hemisphere of humans may play a more dominant role in processing egocentric information than the left hemisphere. However, previous studies of egocentric discrimination mainly focused on assessing the accuracy of egocentric judgment, leaving its timing unexplored. In addition, most previous studies never monitored the subjects' eye position during the experiments, so the influence of eye position on egocentric judgment could not be excluded. In the present study, we systematically assessed the processing of egocentric information in healthy human subjects by measuring the location of their visual subjective straight ahead (SSA) and their manual reaction time (RT) during fixation (monitored by eye tracker). In an egocentric discrimination task, subjects were required to judge the position of a visual cue relative to the subjective mid-sagittal plane and respond as quickly as possible. We found that the SSA of all subjects deviated to the left side of the body mid-sagittal plane. In addition, all subjects but one showed the longest RT at the location closest to the SSA; and in population, the RTs in the left visual field (VF) were longer than that in the right VF. These results might be due to the right hemisphere's dominant role in processing egocentric information, and its more prominent representation of the ipsilateral VF than that of the left hemisphere.

Programming of left hand exploits task set but that of right hand depends on recent history

There are many differences between the left hand and the right hand. But it is not clear if there is a difference in programming between left hand and right hand when the hands perform the same movement. In current study, we carried out two experiments to investigate whether the programming of two hands was equivalent or they exploited different strategies. In the first experiment, participants were required to use one hand to grasp an object with visual feedback or to point to the center of one object without visual feedback on alternate trials, or to grasp an object without visual feedback and to point the center of one object with visual feedback on alternating trials. They then performed the tasks with the other hand. The result was that previous pointing task affected current grasping when it was performed by the left hand, but not the right hand. In experiment 2, we studied if the programming of the left (or right) hand would be affected by the pointing task performed on the previous trial not only by the same hand, but also by the right (or left) hand. Participants pointed and grasped the objects alternately with two hands. The result was similar with Experiment 1, i.e., left-hand grasping was affected by right-hand pointing, whereas right-hand grasping was immune from the interference from left hand. Taken together, the results suggest that when open- and closed-loop trials are interleaved, motor programming of grasping with the right hand was affected by the nature of the online feedback on the previous trial only if it was a grasping trial, suggesting that the trial-to-trial transfer depends on sensorimotor memory and not on task set. In contrast, motor programming of grasping with the left hand can use information about the nature of the online feedback on the previous trial to specify the parameters of the movement, even when the type of movement that occurred was quite different (i.e., pointing) and was performed with the right hand. This suggests that trial-to-trial transfer with the left hand depends on some sort of carry-over of task set for dealing with the availability of visual feedback.

Do left hand reaction time advantages depend on localising unpredictable targets?

Asymmetries in hand movements have routinely been attributed to properties of the two cerebral hemispheres. In right-handed participants, the non-dominant left hand tends to have shorter reaction times, with the dominant right hand achieving shorter movement durations as well as higher peak velocities. The root cause of the surprising left hand RT effect has been debated, largely in the context of right hemisphere specialisation in attention, visuospatial abilities, or "premotor" processes. Mieschke et al. (Brain Cognit 45:1, 2001) and Barthélémy and Boulinguez ( Behav Brain Res 133:1, 2002) both tried to dissociate "premotor" processes explaining the left hand RT advantage, using reaching paradigms where at least one condition required target detection, but no visually guided aiming movement. Unfortunately, the studies obtained conflicting results and conclusions. In the present study, we attempted to re-examine this kind of paradigm with methodological improvements, such as using a task with higher visuospatial demands. Our results demonstrate that whilst RTs are longer as movement complexity increases across three conditions, the left hand RT advantage is present across all conditions-and no significant interaction between hand and condition was found. No significant hand differences were found in peak velocity or duration. These results suggest that the left hand RT advantage cannot be due to movement planning advantages of the right hemisphere, and instead should be attributed to sustained attention/vigilance lateralisation to the right cerebral hemisphere.

The influence of action execution on end-state comfort and underlying movement kinematics: An examination of right and left handed participants

People typically move in an anticipatory manner, planning the intended action in advance to minimize the energy costs associated with producing the action (e.g., Rosenbaum et al., 2009). This is exemplified behaviorally in the end-state comfort effect, which is characterized by the selection of an uncomfortable initial posture to enable a comfortable posture upon completion of the movement (Rosenbaum et al., 1990). The main objective of this study was to further investigate the end-state comfort effect in left- and right-handers (N=20). More specifically, to: (a) understand the influence of mode of action execution; and (b) delineate the role of handedness. The overturned glass task (Fischman, 1997) was used as means of assessment, where participants were asked to demonstrate picking up a glass to pour water in four modes of execution: (1) pantomime without a stimulus; (2) pantomime with image of the glass as a guide; (3) pantomime with glass as a guide; and (4) grasping the glass. End-state comfort was displayed regardless of mode of execution, hand used to complete the task or handedness group. However, kinematic analysis revealed distinct differences, highlighting how movement parameters are altered as a result the mode of action execution.

Relationship of diminished interjoint coordination after stroke to hand path consistency

Differences between 12 left-brain (LCVA, 65.4 ± 11.7 years old) and 10 right-brain (RCVA, 61 ± 12.1 years old) chronic stroke survivors and 10 age-matched control adults in coordinating specific joint motions of the arm to stabilize hand path when reaching to a central target were investigated in this study. The importance of coordinating joints to stabilize hand path was tested by comparing results from uncontrolled manifold (UCM) analysis performed on experimental data versus simulated data where the covariation (coordination) between particular joint motions was removed from the original data set. UCM analysis allowed estimation of the joint configuration variance magnitude that led to hand path variability (V ORT), where the extent of increase in V ORT after removing a joint's covariation indicated how well coordinated its motion actually was with those of the other joints. The more strongly coordinated a joint was with other joints, the greater effect removal of its covariance should have on indices of hand path stability. For the paretic arm of stroke survivors, simulated removal of a joint's covariation, mainly that of shoulder with elbow and wrist, led to less change in the magnitude of V ORT compared to the same arm of control subjects. These findings confirm a reduced ability of the motion of proximal joint from paretic arm to combine flexibly with motions of the distal joints to stabilize hand path.

Are there right hemisphere contributions to visually-guided movement? Manipulating left hand reaction time advantages in dextrals

Many studies have argued for distinct but complementary contributions from each hemisphere in the control of movements to visual targets. Investigators have attempted to extend observations from patients with unilateral left- and right-hemisphere damage, to those using neurologically-intact participants, by assuming that each hand has privileged access to the contralateral hemisphere. Previous attempts to illustrate right hemispheric contributions to the control of aiming have focussed on increasing the spatial demands of an aiming task, to attenuate the typical right hand advantages, to try to enhance a left hand reaction time advantage in right-handed participants. These early attempts have not been successful. The present study circumnavigates some of the theoretical and methodological difficulties of some of the earlier experiments, by using three different tasks linked directly to specialized functions of the right hemisphere: bisecting, the gap effect, and visuospatial localization. None of these tasks were effective in reducing the magnitude of left hand reaction time advantages in right handers. Results are discussed in terms of alternatives to right hemispheric functional explanations of the effect, the one-dimensional nature of our target arrays, power and precision given the size of the left hand RT effect, and the utility of examining the proportions of participants who show these effects, rather than exclusive reliance on measures of central tendency and their associated null hypothesis significance tests.

Development of kinesthetic-motor and auditory-motor representations in school-aged children

In two experiments using a center-out task, we investigated kinesthetic-motor and auditory-motor integrations in 5- to 12-year-old children and young adults. In experiment 1, participants moved a pen on a digitizing tablet from a starting position to one of three targets (visuo-motor condition), and then to one of four targets without visual feedback of the movement. In both conditions, we found that with increasing age, the children moved faster and straighter, and became less variable in their feedforward control. Higher control demands for movements toward the contralateral side were reflected in longer movement times and decreased spatial accuracy across all age groups. When feedforward control relies predominantly on kinesthesia, 7- to 10-year-old children were more variable, indicating difficulties in switching between feedforward and feedback control efficiently during that age. An inverse age progression was found for directional endpoint error; larger errors increasing with age likely reflect stronger functional lateralization for the dominant hand. In experiment 2, the same visuo-motor condition was followed by an auditory-motor condition in which participants had to move to acoustic targets (either white band or one-third octave noise). Since in the latter directional cues come exclusively from transcallosally mediated interaural time differences, we hypothesized that auditory-motor representations would show age effects. The results did not show a clear age effect, suggesting that corpus callosum functionality is sufficient in children to allow them to form accurate auditory-motor maps already at a young age.

Coordination of digit force variability during dominant and non-dominant sustained precision pinch

This study examined the effects of handedness on the inter-digit coordination of force variability with and without concurrent visual feedback during sustained precision pinch. Twenty-four right-handed subjects were instructed to pinch an instrumented apparatus with their dominant and non-dominant hands, separately. During the pinch, the subjects were required to maintain a stable force output at 5 N for 1 min. Visual feedback was given for the first 30 s and removed for the second 30 s. Coefficient of variation and detrended fluctuation analysis were employed to examine the amount and structural variability of the thumb and index finger forces. Similarly, correlation coefficient and detrended cross-correlation analysis were applied to quantify the inter-digit correlation of force amount and structural variability. Results showed that, compared to the non-dominant hand, the dominant hand had higher inter-digit difference in the amount of digit force variability. Without visual feedback, the dominant hand exhibited lower digit force structural variability but higher inter-digit force structural correlation than the non-dominant hand. These results implied that the dominant hand would be more independent, less flexible and with lower dynamic degrees of freedom than the non-dominant hand in coordination of the thumb and index finger forces during sustained precision pinch. The effects of handedness on inter-digit force coordination were dependent on sensory condition, which shed light on higher-level sensorimotor mechanisms that may be responsible for the asymmetries in coordination of digit force variability.

Influence of spatial accuracy constraints on reaction time and maximum speed of performance of unilateral movements

The goal was to study reaction time and maximal velocity of upper limbs of healthy young adults of both sexes during transition from a simple to a more involved task. Performance of dominant and non-dominant arms was recorded. Participants were 43 healthy, right-handed, untrained men (n=22) and women (n=21), 18-22 years old. The simple task required a single jerk-like movement. The involved task required both speed and accuracy where necessity for high speed of performance was emphasized. The effectiveness of transition between tasks was calculated for both reaction time and maximal velocity. No lateral differences were found. Men usually had a shorter reaction time on both tasks and a higher maximal velocity in the simple task. Women were more effective at modifying velocity.

Attentional asymmetries - cause or consequence of human right handedness?

It is well established that the vast majority of the population favors their right hand when performing complex manual tasks. However, the developmental and evolutionary underpinnings of human manual asymmetries remain contentious. One often overlooked suggestion is that right handedness may stem from an asymmetrical bias in attention, with the right hand being allocated more attentional resources during bimanual tasks than the left hand (Peters, 1981). This review examines the evidence for attentional asymmetries during a variety of bimanual tasks, and critically evaluates the explanatory power of this hypothesis for explaining the depth and breadth of individual- and population-level manual asymmetries. We conclude that, while the attentional bias hypothesis is well-supported in adults, it requires further validation from a developmental perspective to explain the full breadth of adult manual laterality.

Eating interrupted: the effect of intent on hand-to-mouth actions

Evidence from recent neurophysiological studies on nonhuman primates as well as from human behavioral studies suggests that actions with similar kinematic requirements but different end-state goals are supported by separate neural networks. It is unknown whether these different networks supporting seemingly similar reach-to-grasp actions are lateralized, or if they are equally represented in both hemispheres. Recently published behavioral evidence suggests certain networks are lateralized to the left hemisphere. Specifically, when participants used their right hand, their maximum grip aperture (MGA) was smaller when grasping to eat food items than when grasping to place the same items. Left-handed movements showed no difference between tasks. The present study investigates whether the differences between grasp-to-eat and grasp-to-place actions are driven by an intent to eat, or if placing an item into the mouth (sans ingestion) is sufficient to produce asymmetries. Twelve right-handed adults were asked to reach to grasp food items to 1) eat them, 2) place them in a bib, or 3) place them between their lips and then toss them into a nearby receptacle. Participants performed each task with large and small food items, using both their dominant and nondominant hands. The current study replicated the previous finding of smaller MGAs for the eat condition during right-handed but not left-handed grasps. MGAs in the eat and spit conditions did not significantly differ from each other, suggesting that eating and bringing a food item to the mouth both utilize similar motor plans, likely originating within the same neural network. Results are discussed in relation to neurophysiology and development.

Limb dominance results from asymmetries in predictive and impedance control mechanisms

Handedness is a pronounced feature of human motor behavior, yet the underlying neural mechanisms remain unclear. We hypothesize that motor lateralization results from asymmetries in predictive control of task dynamics and in control of limb impedance. To test this hypothesis, we present an experiment with two different force field environments, a field with a predictable magnitude that varies with the square of velocity, and a field with a less predictable magnitude that varies linearly with velocity. These fields were designed to be compatible with controllers that are specialized in predicting limb and task dynamics, and modulating position and velocity dependent impedance, respectively. Because the velocity square field does not change the form of the equations of motion for the reaching arm, we reasoned that a forward dynamic-type controller should perform well in this field, while control of linear damping and stiffness terms should be less effective. In contrast, the unpredictable linear field should be most compatible with impedance control, but incompatible with predictive dynamics control. We measured steady state final position accuracy and 3 trajectory features during exposure to these fields: Mean squared jerk, Straightness, and Movement time. Our results confirmed that each arm made straighter, smoother, and quicker movements in its compatible field. Both arms showed similar final position accuracies, which were achieved using more extensive corrective sub-movements when either arm performed in its incompatible field. Finally, each arm showed limited adaptation to its incompatible field. Analysis of the dependence of trajectory errors on field magnitude suggested that dominant arm adaptation occurred by prediction of the mean field, thus exploiting predictive mechanisms for adaptation to the unpredictable field. Overall, our results support the hypothesis that motor lateralization reflects asymmetries in specific motor control mechanisms associated with predictive control of limb and task dynamics, and modulation of limb impedance.

Manual asymmetries in the kinematics of a reach-to-grasp action

In the present study, we manipulated the perceived demand of an ecologically valid task to investigate the possible presence of manual asymmetries in a reach-to-grasp action. Participants reached, grasped and sipped from a water glass under low (nearly empty) and high (nearly full) demand conditions. Participants reached to grasp in closed-loop, open-loop and delay visual conditions. Manual asymmetries were found in movement time, peak velocity and maximum grip aperture variability. Consistent with reach-to-point literature: (1) right-handed actions were completed in less time than left-handed actions in visually and memory-guided conditions; (2) right-handed movements were more accurate (i.e., produced more consistent maximum grip apertures) than left-handed movements in visually guided conditions. The results support a theory of left-hemisphere specialization for visual control of action.

Hemifield or hemispace: what accounts for the ipsilateral advantages in visually guided aiming?

Aiming movements to targets presented on the same side as the reaching limb are faster and more accurate than movements made across the body. These advantages are typically attributed to within-hemisphere sensorimotor control. However, contrary to the within- versus between-hemisphere model, we have shown that some of these advantages tend to go with the side of the movement, rather than the side of the target (Carey et al. Exp Brain Res 112:496-504, 1996; Carey and Otto-de Haart Neuropsychologia 39:894, 2001). Barthélémy and Boulinghez (Exp Brain Res 147:305-312, 2002) acknowledge that our biomechanical account fits data for post-onset movement parameters such as peak velocity and duration, yet they report evidence for some within- versus between-hemisphere contributions to reaction time (RT) advantages. To examine a possible difference between early and late movement kinematics fitting these alternative models, we have dissociated field and space in a different way, which required arm movements with differential inertial consequences, as well as unpredictability of target location in terms of visual field. The data suggest that visual field may contribute some of the variance to hemispatial effects, but only for the right hand. In a second experiment, we used an antipointing task to examine hemispatial versus visual field effects on RTs and to revisit the possible hand difference identified in experiment 1. We found that hemispace accounted for all of the ipsilateral advantages, including RT, for both right and left hands. Results are discussed in terms of the computational requirements of eye-hand coordination in relative unconstrained conditions.

Diminished joint coordination with aging leads to more variable hand paths

Differences in joint coordination between arms and due to aging were studied in healthy young and older adults reaching to either a fixed, central target or to the same target when it could unexpectedly change location after reach initiation. Joint coordination was investigated by artificially removing the covariation of each joint's motions with other joints' motions. Uncontrolled manifold analysis was used to partition joint configuration variance into variance reflecting motor abundance (VUCM) and variance causing hand path variability (VORT). The extent to which VORT, related to the consistency of the hand path, increased after removing a joint's covariation indicated the strength of its coordination with other joints. Young adults exhibited stronger indices of joint coordination, evidenced by a larger increase in VORT after removing joint covariation than for older adults. This effect was more striking for the dominant right compared to the left arm for young adults, but not for older adults, especially with target uncertainty. The results indicate that interjoint coordination in young adults leads to less hand path variability compared to older adults.

Asymmetric Influence of Egocentric Representation onto Allocentric Perception

Objects in the visual world can be represented in both egocentric and allocentric coordinates. Previous studies have found that allocentric representation can affect the accuracy of spatial judgment relative to an egocentric frame, but not vice versa. Here we asked whether egocentric representation influenced the processing speed of allocentric perception. We measured the manual reaction time of human subjects in a position discrimination task in which the behavioral response purely relied on the target's allocentric location, independent of its egocentric position. We used two conditions of stimulus location: the compatible condition-allocentric left and egocentric left or allocentric right and egocentric right; the incompatible condition-allocentric left and egocentric right or allocentric right and egocentric left. We found that egocentric representation markedly influenced allocentric perception in three ways. First, in a given egocentric location, allocentric perception was significantly faster in the compatible condition than in the incompatible condition. Second, as the target became more eccentric in the visual field, the speed of allocentric perception gradually slowed down in the incompatible condition but remained unchanged in the compatible condition. Third, egocentric-allocentric incompatibility slowed allocentric perception more in the left egocentric side than the right egocentric side. These results cannot be explained by interhemispheric visuomotor transformation and stimulus-response compatibility theory. Our findings indicate that each hemisphere preferentially processes and integrates the contralateral egocentric and allocentric spatial information, and the right hemisphere receives more ipsilateral egocentric inputs than left hemisphere does.

Early manifestations of manual specialisation in infants: a longitudinal study from 20 to 30 weeks

This longitudinal study examined lateral differences between latency time of the two hands during the development of prehension in 12 infants from 20 to 30 weeks. Latency time (LT) is defined as the delay between the visual localisation of a reachable target and the beginning of the movement and could be considered as a phase in the preparation of action. If LT varies with the hand used and the type of movement, this would suggest differences in information processing (nature and/or quantity). Results show that the latency time is shorter for the left hand approach movements and shorter for the right hand grasping movements. These findings are in favour of a manual specialisation--clearly present from 20 weeks--and are discussed in a possible hemispheric specialisation perspective.

Processing of hand-related verbs specifically affects the planning and execution of arm reaching movements

Even though a growing body of research has shown that the processing of action language affects the planning and execution of motor acts, several aspects of this interaction are still hotly debated. The directionality (i.e. does understanding action-related language induce a facilitation or an interference with the corresponding action?), the time course, and the nature of the interaction (i.e. under what conditions does the phenomenon occur?) are largely unclear. To further explore this topic we exploited a go/no-go paradigm in which healthy participants were required to perform arm reaching movements toward a target when verbs expressing either hand or foot actions were shown, and to refrain from moving when abstract verbs were presented. We found that reaction times (RT) and percentages of errors increased when the verb involved the same effector used to give the response. This interference occurred very early, when the interval between verb presentation and the delivery of the go signal was 50 ms, and could be elicited until this delay was about 600 ms. In addition, RTs were faster when subjects used the right arm than when they used the left arm, suggesting that action–verb understanding is left-lateralized. Furthermore, when the color of the printed verb and not its meaning was the cue for movement execution the differences between RTs and error percentages between verb categories disappeared, unequivocally indicating that the phenomenon occurs only when the semantic content of a verb has to be retrieved. These results are compatible with the theory of embodied language, which hypothesizes that comprehending verbal descriptions of actions relies on an internal simulation of the sensory–motor experience of the action, and provide a new and detailed view of the interplay between action language and motor acts.

Synergistic control of joint angle variability: influence of target shape

Reaching movements are often used to study the effectiveness of motor control processes with respect to the final position of arm and hand. Empirical evidence shows that different targets can be grasped with similar final position accuracy. However, movements that achieve similar accuracy at their final position may nevertheless be controlled differently. In particular, control strategies may differ in the control of the abundant degrees of freedom with respect to the task-specific costs. The objective of the present study was to investigate whether the applied control strategy was influenced by the shape of the target to be grasped. It was investigated whether mechanical constraints, imposed on final hand orientation or final hand position by the shape of the targets, affected the synergistic coordination of the kinematic degrees of freedom of the arm. Subjects were asked to grasp either a cylindrical or a spherical target, which imposed different constraints on final hand orientation and position. Besides temporal movement aspects, variability of the joint angles of the arm, as well as variability of hand orientation and hand position was analyzed over the whole time course of movement execution, using the uncontrolled manifold method. Overall movement duration differed between cylindrical and spherical target condition, due to differences in deceleration duration. Reaching movements towards the cylindrical target, which was more constraint in final hand orientation and position, took longer than movements towards the spherical target. Analysis further revealed that the degrees of freedom of the arm were synergistically coordinated to stabilize both hand orientation and hand position, when grasping either the spherical or the cylindrical target. This suggests that the applied control strategy in natural reaching movements can simultaneously account for multiple task constraints. The analysis further revealed that stabilization of hand orientation was stronger when reaching towards a cylindrical target, which imposed more constraints on final hand orientation. In contrast, hand position was more strongly stabilized in the spherical target shape condition, where stronger constraints on final hand position were applied. This suggests that different target shapes do influence the control strategy of reaching movements even though variability at movement end was not affected.

Dynamic dominance varies with handedness: reduced interlimb asymmetries in left-handers

Our previous studies of interlimb asymmetries during reaching movements have given rise to the dynamic-dominance hypothesis of motor lateralization. This hypothesis proposes that dominant arm control has become optimized for efficient intersegmental coordination, which is often associated with straight and smooth hand-paths, while non-dominant arm control has become optimized for controlling steady-state posture, which has been associated with greater final position accuracy when movements are mechanically perturbed, and often during movements made in the absence of visual feedback. The basis for this model of motor lateralization was derived from studies conducted in right-handed subjects. We now ask whether left-handers show similar proficiencies in coordinating reaching movements. We recruited right- and left-handers (20 per group) to perform reaching movements to three targets, in which intersegmental coordination requirements varied systematically. Our results showed that the dominant arm of both left- and right-handers were well coordinated, as reflected by fairly straight hand-paths and low errors in initial direction. Consistent with our previous studies, the non-dominant arm of right-handers showed substantially greater curvature and large errors in initial direction, most notably to targets that elicited higher intersegmental interactions. While the right, non-dominant, hand-paths of left-handers were slightly more curved than those of the dominant arm, they were also substantially more accurate and better coordinated than the non-dominant arm of right-handers. Our results indicate a similar pattern, but reduced lateralization for intersegmental coordination in left-handers. These findings suggest that left-handers develop more coordinated control of their non-dominant arms than right-handers, possibly due to environmental pressure for right-handed manipulations.

Motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task

The issue of handedness has been the topic of great interest for researchers in a number of scientific domains. It is typically observed that the dominant hand yields numerous behavioral advantages over the non-dominant hand during unimanual tasks, which provides evidence of hemispheric specialization. In contrast to advantages for the dominant hand during motor execution, recent research has demonstrated that the right hand has advantages during motor planning (regardless of handedness), indicating that motor planning is a specialized function of the left hemisphere. In the present study we explored hemispheric advantages in motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task. Replicating previous findings, both motor planning and execution was influenced by object end-orientation congruency. In addition, although motor planning (i.e., end-state comfort) was not influenced by hand or handedness, motor execution differed between left and right hand, with shorter object transport times observed for the left hand, regardless of handedness. These results demonstrate that the hemispheric advantages often observed in unimanual tasks do not extend to discrete bimanual tasks. We propose that the differences in object transport time between the two hands arise from overt shifting visual fixation between the two hands/objects.

Effect of auditory feedback differs according to side of hemiparesis: a comparative pilot study

Background

Following stroke, patients frequently demonstrate loss of motor control and function and altered kinematic parameters of reaching movements. Feedback is an essential component of rehabilitation and auditory feedback of kinematic parameters may be a useful tool for rehabilitation of reaching movements at the impairment level. The aim of this study was to investigate the effect of 2 types of auditory feedback on the kinematics of reaching movements in hemiparetic stroke patients and to compare differences between patients with right (RHD) and left hemisphere damage (LHD).

Methods

10 healthy controls, 8 stroke patients with LHD and 8 with RHD were included. Patient groups had similar levels of upper limb function. Two types of auditory feedback (spatial and simple) were developed and provided online during reaching movements to 9 targets in the workspace. Kinematics of the upper limb were recorded with an electromagnetic system. Kinematics were compared between groups (Mann Whitney test) and the effect of auditory feedback on kinematics was tested within each patient group (Friedman test).

Results

In the patient groups, peak hand velocity was lower, the number of velocity peaks was higher and movements were more curved than in the healthy group. Despite having a similar clinical level, kinematics differed between LHD and RHD groups. Peak velocity was similar but LHD patients had fewer velocity peaks and less curved movements than RHD patients. The addition of auditory feedback improved the curvature index in patients with RHD and deteriorated peak velocity, the number of velocity peaks and curvature index in LHD patients. No difference between types of feedback was found in either patient group.

Conclusion

In stroke patients, side of lesion should be considered when examining arm reaching kinematics. Further studies are necessary to evaluate differences in responses to auditory feedback between patients with lesions in opposite cerebral hemispheres.

Does hand dominance affect the use of motor abundance when reaching to uncertain targets?

This study investigated hemispheric differences in utilizing motor abundance to achieve flexible patterns of joint coordination when reaching to uncertain target locations. Right-handed participants reached with each arm to the same central target when its final location was certain or when there was a 66% probability that its location could change after movement initiation. Use of greater motor abundance was observed when participants reached to the central target under target location uncertainty regardless of the arm used to reach. Joint variance associated with variability of movement direction was larger when reaching with the left, non-dominant arm. This arm also exhibited higher hand path variability compared to the dominant arm. These arm differences were not found when the final (central) target location was known in advance. The results provide preliminary evidence for a greater ability of the dominant (right) arm/left hemisphere to decouple directions in joint space. That is, to increase the use of motor abundance without simultaneously inducing unwanted hand path variability requires that joint variations be restricted to a limited subspace of joint space. Hemispheric differences in motor planning did not appear to account for arm differences related to the use of motor abundance.

Manual asymmetries in the temporal and spatial control of aimed movements

Right-handed participants performed aimed, left- and right-hand movements toward a fixed target in speed and precision conditions. The purpose was to determine detailed hand differences in the temporal and spatial control during the course of a movement. The results showed that hand differences pertaining to spatial control of movement direction occurred throughout movement execution, and that these differences were stronger in the high speed and low precision conditions. Furthermore, the left hand took more time to execute a movement than the right hand, especially in conditions of low speed and high precision. Detailed time analysis revealed that slowing down of the left hand specifically happened prior to peak acceleration and beyond peak deceleration. These detailed temporal hand differences reoccurred as additional discontinuities in the acceleration profile. These results suggest that the left hand has more difficulty at movement start than the right hand, possibly in overcoming initial inertia. It is discussed whether time-based manual asymmetries located near the end of movement execution should be explained in terms of increased feedback use, or should be related to hand differences regarding the possible active dissipation of mechanical energy at movement completion.

Upper Limb Asymmetries in the Matching of Proprioceptive Versus Visual Targets

The purpose of the current study was to determine the extent to which “sensory dominance” exists in right-handers with respect to the utilization of proprioceptive versus visual feedback. Thirteen right-handed adults performed two target-matching tasks using instrumented manipulanda. In the proprioceptive matching task, the left or right elbow of blindfolded subjects was passively extended by a torque motor system to a target position and held for 3 s before being returned to the start position. The target angle was then matched with either the ipsilateral or contralateral arm. In the second task, visual matching, circular targets were briefly projected to either side of a visual fixation point located in front of the subject. Subjects then matched the target positions with a laser pointer by moving either the ipsilateral or contralateral arm. Overall, marked arm differences in accuracy were seen based on the type of sensory feedback used for target presentation. For the proprioceptive matching task errors were smaller for the nonpreferred left arm, whereas during the visual matching task smaller errors were found for the preferred right arm. These results suggest a left arm/right hemisphere advantage for proprioceptive feedback processing and a right arm/left hemisphere advantage for visual information processing. Such asymmetries may reflect fundamental differences between the two arm/hemisphere systems during the performance of bimanual tasks where the preferred arm requires visual guidance to manipulate an object, whereas the nonpreferred stabilizes that object on the basis of proprioceptive feedback.

Constant error in aiming movements without visual feedback is higher in the preferred hand

There is convincing evidence for a left hand advantage for the spatial planning of aiming movements in right-handers. However, little is known about equivalent proficiency in left-handers. Therefore, 48 participants (24 right-handers and 24 left-handers) performed aiming movements of the hand without visual feedback. While the variable aiming error tended to be lower for the preferred hand, the constant aiming error was consistently lower for the non-preferred hand. Data are consistent with the idea of a spatial accuracy advantage for the controller of the non-preferred hand. Data from an ambidextrous participant suggest that this functional difference might be innate rather than acquired through practice.

Task-dependent asymmetries in the utilization of proprioceptive feedback for goal-directed movement

Whereas the majority of studies regarding upper limb asymmetries in motor performance have focused on preferred arm dominance for producing motor output, studies exploring the role of sensory feedback have suggested that the preferred and non-preferred arms are specialized for different aspects of movement. A recent study by Goble et al. (2006) found evidence of a non-preferred left arm (and presumably right hemisphere) proprioceptive dominance for a target matching task that required subjects to both memorize and transfer across hemispheres proprioceptive target information. This paradigm contrasted previous studies of proprioceptive matching asymmetry that explored only memory-based matching and produced equivocal results. The purpose of the present study, therefore, was to examine task-dependent asymmetries in proprioceptive matching performance, including differences related to active versus passive presentation of the matching target. It was found that the non-preferred left arm of right handers matched target elbow angles more accurately than the preferred arm, but only in the matching condition that required both memory and interhemispheric transfer. Task-dependent asymmetries were not affected by the mode of target presentation and assessment of matching kinematics revealed differences in strategy for both the speed and smoothness of targeted movements. Taken together, these results suggest that the non-preferred arm/hemisphere system is specialized for the processing of movement-related proprioceptive feedback.

Inhibitory control of reaching movements in humans

Behavioral flexibility provides a very large repertoire of actions and strategies, however, it carries a cost: a potential interference between different options. The voluntary control of behavior starts exactly with the ability of deciding between alternatives. Certainly inhibition plays a key role in this process. Here we examined the inhibitory control of reaching arm movements with the countermanding paradigm. Right-handed human subjects were asked to perform speeded reaching movements toward a visual target appearing either on the same or opposite side of the reaching arm (no-stop trials), but to withhold the commanded movement whenever an infrequent stop signal was presented (stop trials). As the delay between go and stop signals increased, subjects increasingly failed to inhibit the movement. From this inhibitory function and the reaction times of movements in no-stop trials, we estimated the otherwise unobservable duration of the stopping process, the stop signal reaction time (SSRT). We found that the SSRT for reaching movements was, on average, 206 ms and that it varied with the reaching arm and the target position even though the stop signal was a central stimulus. In fact, subjects were always faster to withhold reaching movements toward visual targets appearing on the same side of the reaching arm. This behavior strictly parallels the course of the reaction times of no-stop trials. These data show that the stop and go processes interacting in this countermanding task are independent, but most likely influenced by a common factor when under the control of the same hemisphere. In addition, we show that the point beyond which the response cannot be inhibited, the so-called point-of-no-return that divides controlled and ballistic phases of movement processing, lies after the inter-hemispheric transfer.

Left- versus right-hand tracking performance by right-handed boys and girls: examination of performance asymmetry

This study compared left- versus right-hand performance within healthy, right-handed, 8- or 9-yr.-old boys and girls on a finger-movement tracking task. 38 boys and 38 girls were randomly assigned to use either the left hand first and right hand second or vice versa in tracking a sine wave target with extension and flexion movements of the index finger. The data were analyzed with a three-way analysis of variance with repeated measures followed by pair-wise comparisons with a Bonferroni correction. Analysis yielded a significant hand x test interaction and a significant improvement for subjects tracking with the right hand on Test 1 and left hand on Test 2. No significant change occurred for subjects tracking with the left hand on Test 1 and right hand on Test 2. No interaction was observed with sex as a factor. This study suggests that asymmetry of performance favoring the left hand occurs in right-handed boys and girls during finger-movement tracking.

Hemispheric asymmetry for trajectory perception

Broadly, the right hemisphere is known to be specialized for spatial processing whereas the left hemisphere is known to be specialized for temporal processing. However, it remains unclear how both hemispheres interact when processing spatio-temporal information. This study investigates, from a behavioral point of view, whether spatio-temporal processing involved in trajectory perception generates hemispheric asymmetries. An experimental task requiring the prediction of coincidence between ballistic trajectories and a stationary target was used. Reaction times were analyzed according to various interhemispheric conditions determined by the visual hemifield on which the stimulus was presented and the hand of response. There was shorter reaction time for the left hand than the right hand, and shorter reaction times for the left visual hemifield than the right visual hemifield for both hands. From these findings, it is inferred that there is likely to be right hemisphere specialization for trajectory perception and that this hemispheric asymmetry is independent of handedness.

Orienting visuospatial attention generates manual reaction time asymmetries in target detection and pointing

Right-handers exhibit a left hand advantage in response preparation when pointing to targets. These manual asymmetries are generally attributed to a right hemisphere specialization for spatial processing. More precisely, the left hand reaction time (RT) advantage was recently supposed to reflect specifically the right hemisphere superiority for movement planning. This study proposes to investigate a possible attentional origin for manual RT asymmetries. In a first experiment, we used the covert orienting of attention paradigm to measure subjects' RTs when reaching at targets (pointing task) both in valid, neutral and invalid conditions, either in the left or in the right visual fields and with the left and the right hand. In a second experiment, we applied the same paradigm to a detection task (key-pressing). Results revealed that orienting of attention to spatial locations was more time consuming when responding with the right than with the left hand, whether movement planning was required or not. It is suggested that the right hemisphere dominance for orienting of visuospatial attention account, partly at least, for the RT asymmetries classically observed in manual aiming.

Manual reaction time asymmetries in human subjects: the role of movement planning and attention

Hemispheric asymmetries in spatial processing are generally considered to be responsible for the shorter reaction time (RT) of the left hand classically observed for right-handers when pointing at targets. Surprisingly, despite the special role which the right cerebral hemisphere is known to play in visual attention, the attentional hypothesis for hand movement preparation asymmetries is currently rejected. This study aims to test the respective roles of visual attention and movement planning in the left hand RT advantage for goal-directed movements. Two experiments were conducted with the same subjects, a simple visual detection task and a classical pointing task, using the same lateralized stimuli. Subjects used the left hand and the right hand alternatively in order to react to the stimuli. In the detection task, the reaction consisted of simply releasing a switch as quickly as possible after the appearance of a target, whereas in the pointing task, it consisted of performing lateralized reaching movements towards the same target. The main results of this study revealed left hand shorter RTs for both tasks, emphasizing the role which right hemisphere dominance for visuospatial attention plays in manual aiming asymmetries. Moreover, a direct comparison of the RTs obtained in both experiments showed that the specific cost of movement planning was lower when using the left hand, therefore also revealing right hemisphere dominance for movement planning.