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PubMed1998

Early motor influences on visuomotor transformations for reaching: a positive image of optic ataxia.

Coding of reaching in the cerebral cortex is based on the operation of distributed populations of parietal and frontal neurons, whose main functional characteristics reside in their combinatorial power, i.e., in the capacity for combining different information related to the spatial aspects of reaching. The tangential distribution of reach-related neurons endowed with different functional properties changes gradually in the cortex and defines, in the parieto-frontal network, trends of functional properties. These visual-to-somatic gradients imply the existence of cortical regions of functional overlaps, i.e., of combinatorial domains, where the integration of different reach-related signals occurs. Studies of early coding of reaching in the mesial parietal areas show how somatomotor information, such as that related to arm posture and movement, influences neuronal activity in the very early stages of the visuomotor transformation underlying the composition of the motor command and is not added "downstream" in the frontal cortex. This influence is probably due to re-entrant signals traveling through fronto-parietal-association connections. Together with the gradient architecture of the network and the reciprocity of cortico-cortical connections, this implies that coding of reaching cannot be regarded as a top-down, serial sequence of coordinate transformation, each performed by a given cortical area, but as a recursive process, where different signals are progressively matched and further elaborated locally, due to intrinsic cortical connections. This model of reaching is also supported by psychophysical studies stressing the parallel processing of the different relevant parameters and the "hybrid" nature of the reference frame where they are combined. The theoretical frame presented here can also offer a background for a new interpretation of a well-known visuomotor disorder, due to superior parietal lesions, i.e., optic ataxia. More than a disconnection syndrome, this can now be interpreted as the consequence of the breakdown of the operations occurring in the combinatorial domains of the superior parietal segment of the parieto-frontal network.

Animals↗

PubMed1999

Proximodistal structure of early reaching in human infants.

Nine infants were tested, at the age of onset of reaching, seated on their parent's lap and reaching for a small plastic toy. Kinematic analysis revealed that infants largely used shoulder and torso rotation to move their hands to the toy. Many changes in hand direction were observed during reaching, with later direction changes correcting for earlier directional errors. Approximately half of the infants started many reaches by bringing their hands backward or upward to a starting location that was similar across reaches. Individual infants often achieved highly similar peak speeds across their reaches. These results support the hypothesis that infants reduce the complexity of movement by using a limited number of degrees-of-freedom, which could simplify and accelerate the learning process. The proximodistal direction of maturation of the neural and muscular systems appears to restrict arm and hand movement in a way that simplifies learning to reach.

Biomechanical Phenomena↗

PubMed1990

The reaching reaction in the rat: a part of the digging pattern?

The relationship between acquired lateralized reaching and analogous innate movement patterns was examined in adult rats. In Expt. I, 8 naive rats were trained to reach into a narrow trough-shaped feeder. Analysis of the videorecorded movement showed that the forelimb extension starts 120 ms before the forepaw enters the feeder, lasts 190 ms and can be repeated at 280-ms intervals. Before reaching, the rat assumes a stereotyped posture and inserts its nose into the feeder entrance. Twelve rats used in Expt. II were raised from weaning with limited opportunity to practice manipulative skills. Six of these animals were then trained as in Expt. I. In spite of the lack of experience, they learned the reaching task as efficiently as normal rats. The remaining 6 rats were offered food placed into a wide tunnel-shaped feeder. The animals did not take advantage of the possibility of using both forelimbs, but developed typical lateralized reaching. In Expt. III, 4 rats were trained to retrieve food pellets buried under a layer of sand. The videorecorded digging movement essentially resembled reaching but the two forepaws alternated, the extension amplitude was shorter and the movement was never terminated by grasping. It is concluded that the lateralized reaching develops from modified digging and that the kinship of the two movements accounts for the stereotypy and limited modifiability of the acquired reaction.

Animals↗

PubMed1996

Prehension with trunk assisted reaching.

For prehensile tasks, where objects are located beyond the normal reaching space, the trunk is bent forward to assist in the transport of the wrist to the object. Such task behaviors raise complex motor control issues such as how is the trunk movement incorporated into the motor plan. In this experiment, seated subjects were asked to reach and grasp a small and a large object placed on a table located beyond their maximal reach. Forward trunk bending was required to extend the reach distance. For such reaching movements, the wrist velocity consisted of a bell shape profile similar to those seen when the arm is the sole transport agent. In most trials, the trunk was the first to initiate movement, although there was no strict pattern of initiation order. The transport data showed that trunk and arm movement components were decoupled at the end of the reach. While the object was being grasped and lifted, the trunk continued moving for approximately 180 ms after the grasp. Wrist deceleration time expressed in absolute and relative values was sensitive to object size. The time from maximum peak aperture to the end of wrist movement also was significantly longer for grasping the small compared to the large object. No such relationships were observed for the trunk. Temporal coupling was only observed between the grip and wrist transport component. Time to maximum aperture was significantly correlated with time to peak wrist deceleration and only rarely with time to trunk deceleration peak. When the trunk participates in the transport of the wrist to an object, these findings suggest that only the wrist component is directly related to the achievement of the grasp. While the trunk assisted the arm to reach the object, the kinematic parameter recorded did not reveal any evidence of direct coupling. The presented data suggests that the planning takes place at the level of the hand and that endpoint is the primary variable controlled.

Acceleration↗

PubMed2005

Exploiting interlimb coupling to improve paretic arm reaching performance in people with chronic stroke.

OBJECTIVE: To determine whether paretic arm reaching performance is improved in bilateral compared with unilateral conditions. DESIGN: Cohort study. SETTING: University human performance laboratory. PARTICIPANTS: Thirty-two subjects with chronic stroke (57+/-14y; on Fugl-Meyer Assessment arm score, 37+/-14). INTERVENTION: Unilateral and bilateral reaching. Bilateral tasks included varying levels of weight on the nonparetic hand. MAIN OUTCOME MEASURES: An electromagnetic tracking system recorded hand peak acceleration, velocity, and movement time. A 2-way repeated-measures analysis of variance and Tukey-adjusted pairwise comparisons were used to analyze the results (alpha=.05). RESULTS: Paretic differed significantly from nonparetic peak acceleration and velocity in unilateral reaching but not bilateral reaching. Within limbs, the paretic arm attained a higher peak acceleration (P<.001) and velocity (P=.03) in the bilateral compared with the unilateral task, but movement time was unchanged between tasks. Nonparetic peak acceleration was higher (P=.015), velocity was unchanged, and movement time increased (P=.005) in the bilateral compared with the unilateral task. The addition of a weight to the nonparetic arm during bilateral reaching did not result in further improvement in paretic arm performance. CONCLUSIONS: Interlimb coupling effects during bilateral reaching are retained even after chronic stroke and can be used to produce an immediate improvement in paretic arm reaching performance.

Adult↗

PubMed2004

The effects of skill demands and object position on the distribution of preferred hand reaches.

Performance-based measures of hand preference have been developed as an objective method of examining handedness. Previous research using this method showed that both skill demands and the position of the object in working space affect preferential hand reaching. Specifically, preferred hand reaches predominated in left hemispace, in spite of the biomechanical inefficiency involved in reaching across the body midline. This was mediated by the skill demands, with a higher frequency of preferred hand reaches for tasks requiring more skill. To further examine this issue, we increased the task skill demands. Twenty-two right-handed adults reached for five tools located in an array of five positions in front of them. Participants were required to pick up the tool, pick up and demonstrate how to use it, or pick up and actually use the tool on the materials provided. The results showed that the frequency of right hand reaches was greatest for the tool use condition. This effect was mediated by the position of the object in hemispace, with more right hand reaches occurring for the Use task in left hemispace than the other tasks, in support of our previous work.

Adult↗

PubMed2005

Pallidal deep brain stimulation and L-dopa do not improve qualitative aspects of skilled reaching in Parkinson's disease.

OBJECTIVE: To determine effects of dopaminergic medication and pallidal deep brain stimulation (DBS) on skilled reach in Parkinson's disease (PD). BACKGROUND: PD is a neurodegenerative disorder affecting motor control. While speed and execution of movements are improved by L-dopa, not all motor symptoms are alleviated. Little is known about the effects of DBS or medication on reaching. DESIGN METHOD: Eight PD patients with unilateral pallidal DBS reached with the contra-lateral hand for a piece of food, placing it in the mouth, and returning to starting position. Testing was performed on no treatment, medication only, DBS only, and combined treatment. Reaches were digitally recorded and analyzed on a 21 point scale adapted from Eshkol-Wachman Notation. Analysis was blinded, with patients compared to age-matched controls. RESULTS: Patients were tested 6-13 months after surgery. All showed significant improvement clinically and in UPDRS (III) scores. The following data were obtained on the reaching scale: normal controls 16.5-21.0 (mean 18.3), no treatment 3.0-12.5 (mean 7.4), medication only 7.0-14.0 (mean 10.3), DBS only 4.5-16.0 (mean 9.2), combined treatment 4.0-15.0 (mean 9.5). The difference between controls and all treatment groups was statistically significant (P<0.005). All aspects of reach were compromised. No significant differences were found among the four conditions. CONCLUSIONS: This study is consistent with accumulating evidence that some aspects of motor performance in PD patients, such as reaching, are resistant to L-dopa. Also, pallidal DBS does not improve those parameters that are resistant to L-dopa, either alone or in combination with medication.

Adult↗

PubMed2004

Scaling affordances for human reach actions.

A methodology developed by Cesari and Newell [Cesari, P., & Newell, K. M. (1999). The scaling of human grip configuration. Journal of Experimental Psychology: Human Perception and Performance 25, 927-935; Cesari, P., & Newell, K. M. (2000). The body-scaling of grip configurations in children aged 6-12 years. Developmental Psychobiology 36, 301-310] was used to delineate the roles of an object's weight (W) and distance (D) as well as the actor's strength (S) in determining the macroscopic action used to reach for the object. Participants reached for objects of five different weights placed at 10 distances. The findings of a single discriminant analysis revealed that when object weight is scaled in terms of each individual's strength and reach distance is scaled in terms of each individual's maximum-seated reach distance, a single discriminant analysis was able to predict 90% of the reach modes used by both men and women. The result of the discriminant analysis was used to construct a body-scaled equation, K=lnD+ln(W/S)/36, similar in form to the one derived by Cesari and Newell, accurately predicted the reach action used. Our findings indicate that Cesari and Newell's method can identify a complex relationship between geometric and dynamic constraints that determine the affordances for different reach actions.

Adult↗

PubMed2006

Coordination and timing of spine and hip joints during full body reaching tasks.

Coupling of spine and hip joints during full body reaching tasks was investigated in 16 participants (8 male and 8 female) who performed reaching tasks at comfortable and fast-paced movement speeds to three targets located in a para-sagittal plane. The participants paused at target contact for 500ms and then returned to an upright posture. Three-dimensional joint motions of the spine and hip were recorded using an electromagnetic tracking device. We found an effect of movement phase (i.e., reach and return) on the onset timing of the spine and hip joints. For most target locations and movement speeds, spine motion onset preceded hip motion onset during the reaching phase of the movement task. In the reach phase, when averaged across all movement conditions, spine joint motion preceded hip joint motion by an average of 48.9ms. In contrast, in the return phase, hip joint motion preceded spine joint motion by an average of 63.0ms. Additionally, when participants were instructed to use either a knee flexion or knee extension strategy to perform the reaching tasks there was no effect of movement strategy on timing of the spine and hip. There was also no effect of target height on the spine-hip ratio, but as movement speed increased, the spine/hip ratio decreased for all target locations due primarily to an increase in hip joint excursion. The findings indicate clear differences in onset timing of the spine and hip joints during reaching tasks that necessitate some forward bending of the trunk and that onset timing is reversed for the return to an upright posture.

Adult↗

PubMed2006

The impact of object size and rigidity on infant reaching.

Although the changes in kinematics of infant reaching have been studied, few researchers have investigated the improvement of reaching regarding objects of distinct physical properties. The aim of this longitudinal study was to verify the impact of object size and rigidity on the development of reaching in 4-6-month-old infants. Four infants were observed with a motion capture system during trials with four objects of distinct sizes and rigidity. A total of 188 reaches were analyzed by using the 3D movement reconstruction. Our results showed that reaching frequency, mean velocity, and straightness index increased with age. The number of movement units decreased with age and increased for small objects. Rigidity was not shown to affect reaching trajectories. These findings suggest that infants are capable of perceiving the more relevant object properties, thus using their available motor capabilities to modify the essential variables so that they can reach the target more accurately.

Distance Perception↗

PubMed2004

Different Gestalt processing for different actions? Comparing object-directed reaching and looking time measures.

Six experiments compared the Gestalt processing that mediates infant reaching and looking behaviors. Experiment 1 demonstrated that the positioning and timing of 8- and 9-month-olds' reaching was influenced by remembered relative motion. Experiment 2 suggested that a visible gap, without this relative motion, was not sufficient to produce these effects. Experiment 3 found that 6- and 7-month-olds required both remembered relative motion and a continuously visible gap to affect reaching; when two separate objects were placed adjacent to one another, they were treated as though they were connected. Experiments 4 and 5, using a looking time measure, identified a dissociation between looking and reaching performance. In Experiment 6, 6- and 7-month-olds' reaching was influenced when display parts differed in shape and color. In these experiments, Gestalt processing for looking was more influenced by remembered information than was Gestalt processing for reaching. For reaching, a low weighting of separation cues was also apparent.

Female↗

PubMed2000

A kinematic study of contextual effects on reaching performance in persons with and without stroke: influences of object availability.

OBJECTIVE: To examine the effects of context on reaching performance in neurologically impaired and intact populations. Context was varied by the presence or absence of objects used to complete a task. DESIGN: A counterbalanced repeated-measures design. SETTING: A motor control laboratory in a university setting. PARTICIPANTS: Fourteen persons with stroke and 25 neurologically intact adults. INTERVENTIONS: Each participant was tested under two conditions: the presence of the object, in which the participant reached forward with the impaired arm (or corresponding arm) to scoop coins off the table into the other hand; and the absence of the object, in which the participant reached forward to the place where the coins would be placed in the condition of object present. MAIN OUTCOME MEASURES: Kinematic Variables of movement time, total displacement, peak velocity, percentage of reach where peak velocity occurs, and movement units (derived from acceleration data) for reaching tasks. RESULTS: The condition of using real objects elicited kinematically better performance of reaching movements than the condition of performing movements without relevant objects present. Better performance was reflected by shorter movement time, less total displacement, higher peak velocity, greater percentage of reach where peak velocity occurs, and fewer movement units. CONCLUSION: The results of this study showed that the condition of object present elicited better performance of movements represented by kinematic variables than the condition of object absent. The clinical implication is that the use of real and functional objects might be an effective way of facilitating efficient, smooth, and coordinated movement with the impaired arm in persons with stroke. This study, however, should be replicated and extended to confirm the validity of its findings and to allow for generalization in various functional activities.

Adult↗

PubMed1997

Reaching with cerebral tunnel vision.

We studied reaching movements in a 48-year-old man with bilateral lesions of the calcarine cortex which spared the foveal representation and caused severe tunnel vision. Three-dimensional (3D) reconstruction of brain MR images showed no evidence of damage beyond area 18. The patient could not see his hand during reaching movements, providing a unique opportunity to test the role of peripheral visual cues in limb control. Optoelectronic recordings of upper limb movements showed normal hand paths and trajectories to fixated extrinsic targets. There was no slowing, tremor, or ataxia. Self-bound movements were also preserved. Analyses of limb orientation at the endpoints of reaches showed that the patient could transform an extrinsic target's visual coordinates to an appropriate upper limb configuration for target acquisition. There was no disadvantage created by blocking the view of the reaching arm. Moreover, the patient could not locate targets presented in the hemianopic fields by pointing. Thus, residual nonconscious vision or 'blindsight' in the aberrant fields was not a factor in our patient's reaching performance. The findings in this study show that peripheral visual cues on the position and velocity of the moving limb are not critical to the control of goal directed reaches, at least not until the hand is close to target. Other cues such as kinesthetic feedback can suffice. It also appears that the visuomotor transformations for reaching do not take place before area 19 in humans.

Cerebrovascular Disorders↗

PubMed1998

Postural control during reaching in young infants: a dynamic systems approach.

We conceptualize the coordinated development of posture and reaching within Schöner's (Ecological Psychology, 7:291-314, 1995) dynamic model of coupled levels of control: load, timing, and goal. In particular, the goal of postural stability must be maintained during a reach. Using longitudinal data from four infants followed from 3 weeks to 1 year, we show that coordination of the head with upper and lower arm activity is critical for successful reaching. First, infants acquire stable head control several weeks before reaching onset. Furthermore, reaching onset is characterized by a reorganization of muscle patterns to include more trapezius and deltoid activity, serving to stabilize the head and shoulder and provide a stable base from which to reach. We argue that initially, the system is working on postural stability and reaching as goals. Infants secondarily select appropriate muscle patterns to achieve those goals depending, in part, on their individual body sizes, body proportions and energy levels. Motor development proceeds as a continual dialogue between the nervous system, body, and environment.

Humans↗

PubMed1992

Skilled reaching in rats and humans: evidence for parallel development or homology.

Forelimb reaching by the rat is used as a paradigm for the experimental study of neural control, plasticity, and recovery of function after injury, in the expectation that results are generalizable to humans. The present study was done to compare rat to human reaching movements. The movements of both species were videorecorded and subjected to frame-by-frame analysis using Cartesian (spatial and velocity) and Eshkol-Wachman Movement Notation (EWMN) systems. The component movements of reaching, their sequence and velocity profiles, and their topography were similar in the two species. Both species also displayed more supination and lengthened grasping times when reaching for small as opposed to large objects. Both rats and humans moved the limb medially using the upper arm to aim it when they were required to reach through an aperture but in a free reaching test only rats continued to aim the limb. Human movements were characterized by greater blending of movement components, more variability, and independent digit use. Arguments are presented that the similarities and differences in rat and human reaching are not trivially accounted for by limb and task similarities. The many similarities in the movements of the two species provide evidence for at least parallel development or perhaps even homology.

Adult↗

PubMed1999

Kinematic characterization of standing reach: comparison of younger vs. older subjects.

OBJECTIVE: To characterize typical spinal motions that occur during standing reach and to describe differences in spinal motions and center of pressure displacements during reach between younger and older healthy adults. DESIGN: Exploratory, cross sectional investigation utilizing video motion and biomechanics force platform analysis. BACKGROUND: Standing reach provides a means for assessing both arm function and balance control in the context of a common functional activity. The interaction between age-related declines in spinal mobility and the spinal motion occurring during reach is poorly understood. The characterization of spinal motions during task performance for healthy subjects of different age groups is an important first step for understanding the relationship between impairments and physical performance in disabled populations. METHODS: Thirty-four subjects ages 20-36 and 33 subjects ages 60-76 participated. Video motion and force plate analysis were used to characterize spinal motion and center of pressure displacements during the functional reach test for younger and older subjects. RESULTS: Spinal motion during standing reach was characterized by forward trunk flexion, lateral trunk flexion, thoracolumbar rotation, and lower body rotation. Younger and older subjects differed (P = 0.05) in the amount of forward trunk flexion and thoracolumbar rotation which occurred but not lower body rotation. Younger subjects displaced their center of pressure further forward (P = 0.0001) and through a greater percentage of their initial base of support (P = 0.0001) than older subjects. CONCLUSION: This study provides the first multiplanar characterization of spinal motion used during standing reach. Significant differences for a number of variables existed between younger and older subjects.

Adult↗

PubMed1999

Visual control of reaching and grasping in infants.

The role of visual input during reaching and grasping was evaluated. Groups of infants (5, 7, and 9 months old) and adults reached for an illuminated object that sometimes darkened during the reach. Behavioral and kinematic measures were assessed during transport and grasp. Both infants and adults could complete a reach and grasp to a darkened object. However, vision was used during the reach when the object remained visible. Infants contacted the object more often when it remained visible, though they had longer durations and more movement units. In contrast, adults reached faster and more precisely during transport and grasp when the object remained visible. Thus, continuous sight of the object was not necessary, but when it was available, infants used it for contacting the object whereas adults used it to reach and grasp more efficiently.

Adult↗

PubMed1975

Comparison of visually guided reaching in normal and deprived infant monkeys.

A stump-tailed macaque, deprived of sight of its hands and body since shortly after birth, appears to be deficient in the accuracy and precision of its visually guided reaching. These deprived monkeys quickly develop adequate reaches if they are allowed to view their hands. To assess the deficit, we developed a method of open-loop testing (no sight of the reaching limb) for use on both an experimental group deprived of sight of limbs and a control group raised under identical restraints but allowed sight of limbs. The results show that the deprived monkeys can learn to reach a given visible target, but the learned reach is not as precise in the training condition or as precise to new target directions as it is for controls. Furthermore, there is little intermanual transfer of reaching skill for the experimentals but nearly 100% transfer for the controls. Finally, experimentals show a loss of precision in retention testing following a lack of practice, but controls do not. We conclude that the differences in visually guided reaching behavior of the two groups is evidence that the normal accuracy results from unconstrained vision of the hands which produces a mapping of the coordinates of motor response onto the space of vision.

Animals↗