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Results for “reaching”

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PubMed2003

Comparison of three different sit and reach tests for measurement of hamstring flexibility in female university students.

BACKGROUND: The sit and reach test is the most common flexibility test used in health related fitness test batteries. OBJECTIVE: To examine and compare three different sit and reach tests as a measure of hamstring flexibility in 102 female students. METHOD: The traditional sit and reach test, the chair sit and reach test, the back saver sit and reach test, and passive straight leg raise were administered in three trials to all 102 students (mean (SD) age 22 (1) years) on the same day. RESULTS: A Pearson correlation coefficient analysis was significant (p<0.01) for the traditional sit and reach test with back saver sit and reach test and flexibility of hamstrings (r = 0.45 and 0.65 for left and right legs, and 0.63 and 0.53 for left and right legs respectively). Also, the back saver sit and reach test for the left (p<0.01) and right (p<0.05) leg was significantly associated with hamstring flexibility (r = 0.37 and 0.25 for the left leg and 0.50 and 0.44 for the right leg respectively). CONCLUSION: The results indicate that the back saver sit and reach test produces reasonably accurate and stable measures of hamstring flexibility. Moreover, it appears that this test is a safe and acceptable alternative to the traditional and chair sit and reach tests as a measure of hamstring flexibility in young women.

Adult↗

PubMed2006

Descending signals from the pontomedullary reticular formation are bilateral, asymmetric, and gated during reaching movements in the cat.

We examined the contribution of neurons within the pontomedullary reticular formation (PMRF) to the control of reaching movements in the cat. We recorded the activity of 127 reticular neurons, including 56 reticulospinal neurons, during movements of each forelimb; 67/127 of these neurons discharged prior to the onset of activity in the prime flexor muscles during the reach of the ipsilateral limb and form the focus of this report. Most neurons (63/67) showed similar patterns and levels of discharge activity during reaches of either limb, although activity was slightly greater during reach of the ipsilateral limb. In 26/67 cells, the initial change in discharge activity was time-locked to the go signal during reaches of either limb; we have argued that this early discharge contributes to the anticipatory postural adjustments that precede movement. In 11/26 cells, the initial change in activity was reciprocal for reaches with the left and right limbs, although activity during the movement was nonreciprocal. Spike-triggered averaging produced postspike facilitation or depression (PSD) in 12/50 cells during reaches of the limb ipsilateral to the recording site and in 17/49 cells during reach of the contralateral limb. Some cells produced PSD in ipsilateral extensor muscles before the start of the reach and during reaches made with the contralateral, but not the ipsilateral limb; this suggests the signal must be differentially gated. Overall, the results suggest a strong bilateral, albeit asymmetric, contribution from the PMRF to the control of posture and movement during voluntary movement.

Animals↗

PubMed2004

Monkey hand postural synergies during reach-to-grasp in the absence of vision of the hand and object.

Understanding how the CNS controls reach-to-grasp will require behavioral and neurophysiological studies of reach-to-grasp in the monkey, including the evaluation of whole-hand grasp with explicit force requirements. In this study, monkeys performed a reach-to-grasp task in which the size, shape, and orientation of the objects were varied. The monkeys were required to grasp each object at five force levels based on visual feedback. Seventeen positions on the wrist and hand were monitored to quantify kinematics. Hand shaping began with initiation of reach and continued throughout the reach, matching object properties even without vision of the hand or object. Grasp aperture scaled to object size. Singular value decomposition analysis of the marker positions identified two dominant hand postures. The first eigenvector or "eigenposture" consisted of an open hand configuration midway between flexion and extension that explained >93% of the variance. The second eigenposture consisted of hyperextension of all joints that accounted for another 4-5% of the variance. The two eigenpostures were similar across force levels and between monkeys. Reach kinematics consisted of a U-shaped hand path with a bell-shaped velocity profile. Trajectory and speed were independent of grasp force and object properties. In summary, hand shaping during the reach occurred without vision of the hand or object, and hand kinematics were not dependent on grasp force. Furthermore, the reach was independent of grasp force and object properties. These observations imply that the kinematics of reach-to-grasp and grasp force are controlled independently. Similar to humans, monkeys may use a simplifying strategy to reduce the degrees of freedom of the hand during reach-to-grasp.

Animals↗

PubMed1995

Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm.

1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur despite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

Adaptation, Physiological↗

PubMed2002

Quantitative and qualitative impairments in skilled reaching in the mouse (Mus musculus) after a focal motor cortex stroke.

BACKGROUND AND PURPOSE: Skilled reaching movements are an important aspect of human motor behavior but are impaired after motor system stroke. The purpose of this study was to document skilled movements in mice before and after a focal motor cortex stroke for the purpose of developing a mouse model of human stroke. METHODS: Male C57/BL6 mice were trained to reach with a forelimb for food pellets and then given a motor cortex stroke, induced by pial stripping, contralateral to their preferred reaching limb. Reaching success and the movements used in reaching were analyzed by frame-by-frame inspection of presurgical and postsurgical video records. RESULTS: Reaching success was severely impaired after the stroke. Improvement in success over 2 postsurgical weeks was moderate. Analysis of 10 movement components comprising reaches pre- and postsurgically indicated that most of the rotatory movements of the limb used for aiming, advancing, pronating, and supinating the paw were impaired. When successful reaches did occur, body movements that compensated for the impairments in limb rotatory movements aided them. CONCLUSIONS: The results indicate that skilled reaching in the mouse is impaired by focal motor cortex stroke and they suggest that the mouse, and the skilled reaching task, provides an excellent model for studying impairments, compensation, and recovery after motor system stroke.

Animals↗

PubMed2006

Recovery of grasp versus reach in people with hemiparesis poststroke.

BACKGROUND AND OBJECTIVE: The authors recently found that grasping was not relatively more disrupted than reaching in people with acute hemiparesis. They now extend this work to the recovery of reach versus grasp. METHODS: Hemiparetic subjects were tested acutely, after 90 days, and then after 1 year poststroke, and a control group was evaluated once. Using kinematic techniques, subjects were studied performing reach and reach-to-grasp movements. The authors quantified 3 characteristics of performance for each movement: speed, accuracy, and efficiency, where an efficient movement was defined as a movement directly to the target without extraneous or abnormally circuitous movements. To evaluate the relative deficits and recovery in reach versus grasp, performance measures were converted to z scores using control group means and standard deviations. RESULTS: The authors' results showed that, starting with small deficits in speed acutely, both reach speed and grasp speed improved over time. Deficits in accuracy were greater in the reach than the grasp acutely, and these deficits lessened such that by the 90-day time point, the relative accuracy of the 2 movements was the same. In contrast, deficits in efficiency were greater in the grasp than the reach acutely, and grasp efficiency did not recover. The majority of recovery in reaching and grasping occurred by the 90-day time point, with little change occurring between the 90-day and 1-year time points. CONCLUSIONS: The authors hypothesize that, in chronic hemiparesis, purposeful movements requiring distal control may be more impaired than purposeful movements requiring proximal control, not because of the initial lesion, but because, over the course of recovery, spared components of the descending motor systems may be able to compensate for the accuracy deficits in reaching (proximal control) but not the efficiency deficits in grasping (distal muscular control).

Adaptation, Physiological↗

PubMed2006

Robot-assisted reaching exercise promotes arm movement recovery in chronic hemiparetic stroke: a randomized controlled pilot study.

BACKGROUND AND PURPOSE: Providing active assistance to complete desired arm movements is a common technique in upper extremity rehabilitation after stroke. Such active assistance may improve recovery by affecting somatosensory input, motor planning, spasticity or soft tissue properties, but it is labor intensive and has not been validated in controlled trials. The purpose of this study was to investigate the effects of robotically administered active-assistive exercise and compare those with free reaching voluntary exercise in improving arm movement ability after chronic stroke. METHODS: Nineteen individuals at least one year post-stroke were randomized into one of two groups. One group performed 24 sessions of active-assistive reaching exercise with a simple robotic device, while a second group performed a task-matched amount of unassisted reaching. The main outcome measures were range and speed of supported arm movement, range, straightness and smoothness of unsupported reaching, and the Rancho Los Amigos Functional Test of Upper Extremity Function. RESULTS AND DISCUSSION: There were significant improvements with training for range of motion and velocity of supported reaching, straightness of unsupported reaching, and functional movement ability. These improvements were not significantly different between the two training groups. The group that performed unassisted reaching exercise improved the smoothness of their reaching movements more than the robot-assisted group. CONCLUSION: Improvements with both forms of exercise confirmed that repeated, task-related voluntary activation of the damaged motor system is a key stimulus to motor recovery following chronic stroke. Robotically assisting in reaching successfully improved arm movement ability, although it did not provide any detectable, additional value beyond the movement practice that occurred concurrently with it. The inability to detect any additional value of robot-assisted reaching may have been due to this pilot study's limited sample size, the specific diagnoses of the participants, or the inclusion of only individuals with chronic stroke.

Journal Article↗

PubMed2002

Effect of task context on reaching performance in children with spastic hemiparesis.

OBJECTIVE: To investigate the effect of task context on the quality of reaching movements in children with spastic hemiparesis. DESIGN: Randomized controlled experimental trial. SETTING: Institute for the Study of Education and Human Development (ISED). SUBJECTS: Twelve children (8-14 years of age) with spastic hemiplegic cerebral palsy. INTERVENTIONS: Subjects made fast reaching movements with the affected or nonaffected arm on a digitizer in three context conditions: (a) reach to press a light switch to turn on a red light (functional), (b) reach to press the light switch; no light (semi-functional), and (c) reach to a marker (nonfunctional). MAIN OUTCOME MEASURES: Kinematics of reaching movements of affected and nonaffected arms: movement time (MT), peak velocity (PV), time to PV, percentage of MT where peak velocity occurred (PPV), and smoothness (i.e. number of movement units (MU)). RESULTS: The functional condition elicited better quality of reaching for the nonaffected, but particularly the affected arm. Reaching of the affected arm was faster (larger MT; F = 10.21, p < 0.01), smoother (fewer MU; F = 19.95, p < 0.001), and better-controlled (right shift of PPV; F = 16.03, p < 0.001) compared with the semi- and nonfunctional condition. Reaching of the nonaffected arm was also faster (longer MT, F = 4.81, p < 0.05), and more smooth (fewer MU, F = 7.23, p < 0.05). CONCLUSIONS: These findings suggest that providing a functional context to perform a task may enhance the quality of reaching movements of the affected arm in children with spastic hemiparesis.

Adolescent↗

PubMed2006

Neural dynamics in monkey parietal reach region reflect context-specific sensorimotor transformations.

We investigated the neural dynamics of sensorimotor transformations in the parietal reach region (PRR) of monkeys. To dissociate sensory from motor goal representations, we used a memory-guided anti-reach task. The monkeys had to reach either to a visually instructed, memorized peripheral target position (pro-reach) or to a diametrically opposed position (anti) while keeping central ocular fixation. Pro- and anti-reaches were randomly interleaved and indicated by a color instruction from the beginning of each trial. We analyzed spatiotemporal single-cell tuning and performed time-resolved population decoding to quantify the dynamic representation of the spatial visual cue, the reach goal, and the currently valid task rule (pro/anti mapping). Sensory information regarding the visual cue position was represented weakly during a short period of cue visibility. PRR predominantly encoded the reach goal from the end of the cue period on. The representation of the reach goal in the memory task evolves later for the anti- compared with pro-reaches, consistent with a 40-50 ms difference in reaction time between the two task rules. The task rule could be decoded before the appearance of the spatial cue, which indicates that abstract rule information is present in PRR that is independent of spatial cue or motor goal representations. Our findings support the hypothesis that PRR immediately translates current sensory information into reach movement plans, rather than storing the memorized cue location in the instructed-delay task. This finding indicates that PRR represents integrated knowledge on spatial sensory information combined with abstract behavioral rules to encode the desired movement goal.

Action Potentials↗

PubMed1993

Visual guidance in infants' reaching toward suddenly displaced targets.

This experiment evaluated the role of visual input about the location of a target object and the location of the hand in reaching by infants and adults. 5- and 9-month-old infants were presented with illuminated toys to reach for in a dark room. On no-switch trials, the toy remained illuminated throughout the infant's reach, whereas on switch trials the first-lit toy was replaced during the reach by a second-lit toy at a different position. On approximately half of the trials of each type a luminescent marker was attached to the reaching hand. Adult subjects (tested without the hand marker) fully compensated to the second-lit toy on switch trials, during a second reaching segment. On switch trials, 9-month-olds partially adjusted to the second-lit toy when wearing the hand marker and did not adjust without it. On no-switch trials, 9-month-olds reached just as accurately with or without the hand marker. 5-month-olds were generally inaccurate in their reaching and were unaffected by the presence or absence of the hand marker. The findings suggest that during the development of reaching there is an increase in visual guidance during the approach phase of reaches.

Adult↗

PubMed2002

Interaction of levodopa and cues on voluntary reaching in Parkinson's disease.

The bradykinesia associated with Parkinson's disease (PD) can be improved by both levodopa and the use of external cues. We examined the combined effect of levodopa and external cueing on the voluntary reaching movements of individuals with PD. Nine subjects with PD and nine matched controls were studied reaching to a ball target. Subjects with PD were studied after being off levodopa overnight and again on their morning dose. Kinematic data were collected as all subjects made both accurate and fast reaches under two different cue conditions: noncued (self-initiated) and cued (triggered by a light). Subjects with PD reached more slowly than controls under all conditions. PD subjects increased their reach velocity and decreased movement time after taking levodopa and also when moving to a cue. However, the effects of levodopa and cueing were not additive. Instead, levodopa improved reach velocity to a greater extent in the noncued vs. cued condition. We also found that levodopa improved accurate (self-paced) reaches more than fast reaches. These data suggest that levodopa may preferentially improve voluntary reaches that are more internally generated.

Antiparkinson Agents↗

PubMed2003

Effects of pallidotomy and levodopa on walking and reaching movements in Parkinson's disease.

We examined the effects of levodopa and unilateral pallidotomy on quantitative measures of walking and reaching in Parkinson's disease (PD). We also compared quantitative measures of movement with standard clinical rating scales. We used kinematic measures and the Unified Parkinson's Disease Rating Scale (UPDRS) motor subscale (subscale III) to evaluate the movement of 10 people with PD. Subjects were tested after withholding PD medications for at least 8 hours and again 30 to 45 minutes after taking the first morning dose of levodopa. They were studied in this manner before unilateral pallidotomy and then 3.5 to 10 months after surgery. The UPDRS motor subscale was performed in each state. Kinematic data were collected as subjects reached to a target and walked. The UPDRS motor subscale ratings were similar to those reported in the literature: pallidotomy improved the overall motor score and the contralateral bradykinesia + rigidity score, but not the gait + posture score. In contrast, kinematic measures demonstrated that levodopa and pallidotomy had different effects on walking and reaching speed. Both treatments improved walking speed, and the effect was additive. Levodopa improved reaching speed before pallidotomy but did not improve it as much after pallidotomy. Additionally, pallidotomy had inconsistent effects on reaching; some subjects were faster and others were slower. The subjects who initially reached more slowly improved after pallidotomy; the subjects who initially reached more normally (faster) worsened after pallidotomy. On the basis of our results, we speculate that basal ganglia output pathways that control walking and reaching may be distinct, such that bilateral projections to the pedunculopontine area influence walking, whereas ipsilateral thalamocortical projections influence reaching.

Aged↗

PubMed1989

Trajectories of reaches to prismatically-displaced targets: evidence for "automatic" visuomotor recalibration.

The present study examined the kinematics of unrestricted reaches to prismatically-displaced targets. The kinematic analysis allowed us (1) to document how and where in the reach adjustments were made to compensate for the prismatic displacement. (2) to detail the changes that occur in the characteristics of reaches during the course of adaptation to the prisms, and (3) to look at the effects of providing information (or not) to the subject about the presence and nature of the prismatic distortion. The experiment differed from classic studies of prism adaptation in that subjects were permitted full visual feedback of their moving limb at all times, and entire reaching movements were recorded in addition to terminal errors. Experimental subjects were tested either with large-displacement prisms of the sort typically used in such experiments (20 diopters) or with small-displacement prisms (5 diopters) the properties of which went undetected in uninformed subjects. By using small displacements, it was possible to examine the process of visuomotor recalibration directly, free of contamination by "conscious" correction strategies. There were no differences in the terminal accuracies of the reaches made by subjects in any of the conditions. The availability of visual feedback allowed subjects to place their finger accurately on the target, despite the fact that in some cases their vision was displaced by as much as 11.4 degrees to the right. When the entire reach was examined, however, it was found that the amount of curvature in the path increased when large or small diopter prisms were unexpectedly introduced, with the subjects showing large deviations to the right. This rightward deviation was corrected in the final approach with a larger terminal correction. On some occasions, nonetheless, corrections were observed very early in the course of the reaching movement and appeared to be part of a natural process of trajectory fine-tuning. Uninformed subjects exposed to either large or small prismatic displacements also showed evidence of adaptation through an increased number of on-line corrections which compensated for a tendency to reach into the side of space opposite to the direction of the displacement (a "negative after-effect" in the path of the reach). Moreover, when questioned after the experiment, it became clear that uninformed subjects exposed to small prismatic displacements had apparently failed to detect any visual displacement whatsoever. Taken together, these results suggest that visuomotor recalibration can take place "automatically" without feedback from terminal errors and without the use of conscious strategies.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗

PubMed1997

The role of posterior parietal cortex in visually guided reaching movements in humans.

Positron emission tomography (PET) was used to identify the brain areas involved in visually guided reaching by measuring regional cerebral blood flow (rCBF) in six normal volunteers while they were fixating centrally and reaching with the left or right arm to targets presented in either the right or the left visual field. The PET images were registered with magnetic resonance images from each subject so that increases in rCBF could be localized with anatomical precision in individual subjects. Increased neural activity was examined in relation to the hand used to reach, irrespective of field of reach (hand effect), and the effects of target field of reach, irrespective of hand used (field effect). A separate analysis on intersubject, averaged PET data was also performed. A comparison of the results of the two analyses showed close correspondence in the areas of activation that were identified. We did not find a strict segregation of regions associated exclusively with either hand or field. Overall, significant rCBF increases in the hand and field conditions occurred bilaterally in the supplementary motor area, premotor cortex, cuneus, lingual gyrus, superior temporal cortex, insular cortex, thalamus, and putamen. Primary motor cortex, postcentral gyrus, and the superior parietal lobule (intraparietal sulcus) showed predominantly a contralateral hand effect, whereas the inferior parietal lobule showed this effect for the left hand only. Greater contralateral responses for the right hand were observed in the secondary motor areas. Only the anterior and posterior cingulate cortices exhibited strong ipsilateral hand effects. Field of reach was more commonly associated with bilateral patterns of activation in the areas with contralateral or ipsilateral hand effects. These results suggest that the visual and motor components of reaching may have a different functional organization and that many brain regions represent both limb of reach and field of reach. However, since posterior parietal cortex is connected with all of these regions, we suggest that it plays a crucial role in the integration of limb and field coordinates.

Adult↗

PubMed2005

Development of reaching in infancy.

The development of reaching for stationary objects was studied longitudinally in 12 human infants: 5 from the time of reach onset to 5 months of age, 5 from 6 to 20 months of age, and 2 from reach onset to 20 months of age. We used linear mixed-effects statistical modeling and found a gradual slowing of reach speed and a more rapid decrease of movement jerk with increasing age. The elbow was essentially locked during early reaching, but was prominently used by 6 months. Differences between infants were distributed normally and no evidence of different types of reachers was found. The current work combined with other longitudinal studies of infant reaching shows that the increase in skill over the first 2 years of life is seen, not by an increase in reaching speed, but by an increase in reach smoothness. By the end of the second year, the overall speed profile of reaching is approaching the typical adult profile where an early acceleration of the hand brings the hand to the region of the target with a smooth transition to a lower-speed phase where grasp is accomplished.

Age Factors↗

PubMed2001

Influence of stimulus color on the control of reaching-grasping movements.

This kinematic study aimed to determine whether color is a stimulus property involved in the control of reaching-grasping movements. Subjects reached and grasped a target-object, located either on the right or on the left of the subject's midline. A distractor, placed along the subject's midline, could be randomly presented. The colors, i.e., both chromaticity (red and green stimuli were presented) and lightness, of the target and distractor were varied in experiment 1. Only stimulus lightness and only stimulus chromaticity were varied in experiments 2 and 3, respectively. In experiment 4 subjects matched with their thumb and index finger the size of the target-stimuli presented in experiment 1. Chromaticity (experiments 1 and 3) of the target and distractor influenced grasp, but not reach. Maximal finger aperture was larger during grasping the red than the green target. Data collected in the matching task (experiment 4) confirmed a trend to overestimate the red target and to underestimate the green one. During grasp, hand shaping was influenced by distractor chromaticity when it was different from target chromaticity. Distractor lightness affected reach, but not grasp (experiments 1 and 2). Reach was slower when the distractor was lighter and arm trajectory veered away from it. The results of the present study suggest that color, that is the ensemble of chromaticity and lightness, is a stimulus property involved in the control of reaching-grasping. The different effects of target color on reach and grasp support the notion that intrinsic object properties, such as color, affect grasp more than reach. In addition, the different effects of distractor chromaticity and lightness on reach and grasp confirm that target-objects are visually extracted from surrounding cues by means of different processes, according to the required motor response.

Adult↗

PubMed1999

Parieto-frontal coding of reaching: an integrated framework.

In the last few years, anatomical and physiological studies have provided new insights into the organization of the parieto-frontal network underlying visually guided arm-reaching movements in at least three domains. (1) Network architecture. It has been shown that the different classes of neurons encoding information relevant to reaching are not confined within individual cortical areas, but are common to different areas, which are generally linked by reciprocal association connections. (2) Representation of information. There is evidence suggesting that reach-related populations of neurons do not encode relevant parameters within pure sensory or motor "reference frames", but rather combine them within hybrid dimensions. (3) Visuomotor transformation. It has been proposed that the computation of motor commands for reaching occurs as a simultaneous recruitment of discrete populations of neurons sharing similar properties in different cortical areas, rather than as a serial process from vision to movement, engaging different areas at different times. The goal of this paper was to link experimental (neurophysiological and neuroanatomical) and computational aspects within an integrated framework to illustrate how different neuronal populations in the parieto-frontal network operate a collective and distributed computation for reaching. In this framework, all dynamic (tuning, combinatorial, computational) properties of units are determined by their location relative to three main functional axes of the network, the visual-to-somatic, position-direction, and sensory-motor axis. The visual-to-somatic axis is defined by gradients of activity symmetrical to the central sulcus and distributed over both frontal and parietal cortices. At least four sets of reach-related signals (retinal, gaze, arm position/movement direction, muscle output) are represented along this axis. This architecture defines informational domains where neurons combine different inputs. The position-direction axis is identified by the regular distribution of information over large populations of neurons processing both positional and directional signals (concerning the arm, gaze, visual stimuli, etc.) Therefore, the activity of gaze- and arm-related neurons can represent virtual three-dimensional (3D) pathways for gaze shifts or hand movement. Virtual 3D pathways are thus defined by a combination of directional and positional information. The sensory-motor axis is defined by neurons displaying different temporal relationships with the different reach-related signals, such as target presentation, preparation for intended arm movement, onset of movements, etc. These properties reflect the computation performed by local networks, which are formed by two types of processing units: matching and condition units. Matching units relate different neural representations of virtual 3D pathways for gaze or hand, and can predict motor commands and their sensory consequences. Depending on the units involved, different matching operations can be learned in the network, resulting in the acquisition of different visuo-motor transformations, such as those underlying reaching to foveated targets, reaching to extrafoveal targets, and visual tracking of hand movement trajectory. Condition units link these matching operations to reinforcement contingencies and therefore can shape the collective neural recruitment along the three axes of the network. This will result in a progressive match of retinal, gaze, arm, and muscle signals suitable for moving the hand toward the target.

Animals↗

PubMed2006

Skilled reaching impairments follow intrastriatal hemorrhagic stroke in rats.

The infusion of autologous blood into the brain of rats is a widely used model of intracerebral hemorrhage (ICH). Careful assessment of functional recovery is an essential part of preclinical testing (e.g., putative cytoprotectants). However, few tests detect long-term deficits in this model. In this study, we used the staircase and single pellet tests to characterize skilled reaching ability after striatal ICH. Rats were trained to reach for food pellets in these tasks before ICH, which was created by infusing 100muL of autologous blood into the striatum. We assessed reaching success in both tasks for 5 days starting 7 and 28 days after ICH. We counted the number of reaching attempts made with each forelimb in the staircase task and performed kinematic analysis of reaching in the single pellet task. The contralateral (to lesion) forelimb reaching success was significantly impaired in the staircase task 1 week after ICH, but this recovered to pre-surgical levels thereafter. Reaching deficits in the single pellet task were more severe and persistent. Detailed analysis of reaches on day 11 revealed several abnormalities in the following movement components: pronation, grasping, supinating the paw and releasing the pellet. At 1 month, only digit opening and supination were impaired. Accordingly, the single pellet task is better at detecting long-term skilled reaching impairments in the whole blood model of ICH. Thus, the single pellet task seems suited to cytoprotection and rehabilitation studies.

Animals↗