Useless, considering something doesn't help at all. The mentors and senior researchers need to be fired for crapola like this. NOTHING HERE HELPS SURVIVORS! All my reaching problems are due to spasticity. And there is NOTHING that cures spasticity.
Mild Stroke Affects Pointing Movements Made in Different Frames of Reference
Abstract
Background
Motor performance is a complex process controlled in task-specific spatial frames of reference (FRs). Movements can be made within the framework of the body (egocentric FR) or external space (exocentric FR). People with stroke have impaired reaching, which may be related to deficits in movement production in different FRs.
Objective
To characterize rapid motor responses to changes in the number of degrees of freedom for movements made in different FRs and their relationship with sensorimotor and cognitive impairment in individuals with mild chronic stroke.
Methods
Healthy and poststroke individuals moved their hand along the contralateral forearm (egocentric task) and between targets in the peripersonal space (exocentric task) without vision while flexing the trunk. Trunk movement was blocked in randomized trials.
Results
For the egocentric task, controls produced the same endpoint trajectories in both conditions (free- and blocked-trunk) by preserving similar shoulder-elbow interjoint coordination (IJC). However, endpoint trajectories were dissimilar because of altered IJC in stroke. For the exocentric task, controls produced the same endpoint trajectories when the trunk was free or blocked by rapidly changing the IJC, whereas this was not the case in stroke. Deficits in exocentric movement after stroke were related to cognitive but not sensorimotor impairment.
Conclusions
Individuals with mild stroke have deficits rapidly responding to changing conditions for complex reaching tasks. This may be related to cognitive deficits and limitations in the regulation of tonic stretch reflex thresholds. Such deficits should be considered in rehabilitation programs encouraging the reintegration of the affected arm into activities of daily living.
Introduction
Reaching movements require perceptual-motor transformations depending on the spatial frame of reference (FR) in which they are performed.1-6 A FR or system of coordinates consists of elements, the positions of which are defined by their distance from a specific point called the origin or referent point. The brain can use different FRs to accomplish motor actions. For example, reaching movements can be directed to a person’s body in an egocentric FR, or away from the body to a target located in external space in an exocentric FR.
Arm trajectories and interjoint coordination (IJC) differ for reaches made in egocentric and exocentric FRs.7 Healthy individuals have no difficulty rapidly changing reaching patterns in different FRs, practically without learning (ie, 1-trial adaptation).8 This behavior illustrates the principle of motor equivalence9: the ability to reach the same motor goal using different combinations of joint rotations, often referred to as kinematic redundancy.10,11 This type of rapid reaction, critical for everyday life, is related to sensory feedback and the cognitive ability to find motor-equivalent solutions through motor problem-solving.5,8,12-15
Egocentric and exocentric reaches involve partially overlapping but different neural structures. The parietal cortex constructs multiple spatial FRs5 and strongly interacts with the frontal cortex (premotor cortex, supplementary eye fields), which encodes object locations in different spatial FRs.16 Egocentric coding is associated with the parietal and frontal cortices, whereas exocentric coding is associated with the temporal cortex.17,18 Damage to the parietal cortex and associated areas, such as that occurring after stroke, may lead to impairments in producing movements in both egocentric and exocentric FRs,19 but rapid motor responsiveness in different FRs has not been investigated.
Upper limb (UL) motor impairment is a common and challenging sensorimotor deficit after stroke.20 Compared with healthy individuals, movements of the affected UL after stroke are generally slower, more variable, more spatially and temporally segmented, and characterized by abnormal patterns of muscle activation and IJC, which may be related to deficits in the regulation of tonic stretch reflex thresholds.21,22 Stroke research has mainly focused on UL reaching in exocentric FRs. For example, in trunk-assisted reaching to beyond-reach exocentric targets, when trunk movement was suddenly arrested, healthy individuals preserved the hand trajectory and reaching accuracy by rapidly modifying shoulder and elbow movements.23 However, those with stroke had difficulty modifying arm joint movements in response to trunk arrest. Only one study assessed differences in egocentric and exocentric movements in poststroke individuals during a finger-to-nose test.7 Individuals with stroke had impaired IJC and used more trunk compensation for both egocentric and exocentric pointing phases compared with controls,7 but the causes of movement deficits in different FRs were not elucidated.
Mechanisms underlying motor deficits after stroke may be better understood using perturbation methods compared with movement description alone.24 Our objective was to identify deficits in producing pointing movements in egocentric and exocentric FRs in individuals with stroke. We hypothesized that individuals with stroke, unlike healthy controls, would have impairments in rapidly modifying shoulder-elbow IJC to reproduce similar reaching trajectories when trunk movements were present or blocked, in both egocentric and exocentric FRs. Because this behavior depends on sensory information and problem-solving, we also hypothesized that deficits in rapid response ability would be related to levels of UL sensorimotor and cognitive impairment. Preliminary results have appeared in abstract form.25
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