Cardiopulmonary response to exercise testing in people with chronic stroke: a retrospective study.

Background and Purpose. This study investigated the cardiopulmonary response and safety of exercise testing at peak effort in people during the chronic stage of stroke recovery. Methods. This retrospective study examined data from 62 individuals with chronic stroke (males: 32; mean (SD); age: (12.0) yr) participating in an exercise test. Results. Both males and females had low cardiorespiratory fitness levels. No significant differences were found between gender for peak HR (P = 0.27), or VO(2) peak (P = 0.29). Males demonstrated higher values for minute ventilation, tidal volume, and respiratory exchange ratio. No major adverse events were observed in the exercise tests conducted. Discussion and Conclusion. There are differences between gender that may play a role in exercise testing performance and should be considered when developing exercise programs. The low VO(2) peak of this cohort of chronic stroke survivors suggests the need for participation in exercise interventions.

Effect of bilateral macular scotomas from age-related macular degeneration on reach-to-grasp hand movement.

PURPOSE: Vision plays a critical role in reaching and grasping objects. Consequently, bilateral macular scotomas from age-related macular degeneration (AMD) may affect reach-to-grasp movements. The purpose of this work was to investigate changes in reach-to-grasp movement dynamics and to relate those changes to the characteristics of subjects' preferred retinal loci (PRL), scotomas, and visual acuities. METHODS: Three-dimensional positions of the index finger and thumb were recorded while subjects with bilateral scotomas and subjects with normal vision reached for and grasped blocks of three widths at two distances under binocular and monocular viewing conditions. Reach-dynamic parameters and the grip aperture (thumb-index finger distance) were calculated. Retinal locations and sizes of subjects' scotomas and PRLs were mapped with a scanning laser ophthalmoscope. RESULTS: Scotoma subjects' hand trajectories had longer movement durations, lower maximum velocities, and longer visual reaction times than those of control subjects. With monocular viewing, maximum grip aperture (MGA) increased as a function of block width at a significantly higher rate for scotoma subjects than for control subjects. MGA decreased with increasing PRL bivariate normal ellipse area, and visual reaction time increased with decreasing acuity of the eye tested. CONCLUSIONS: Compared with normally sighted subjects, subjects with bilateral macular scotomas from AMD have reach-to-grasp movements with longer trajectories, longer visual reaction times, lower velocities, and altered MGA-block width scaling. Visual reaction time and MGA are directly related to PRL characteristics. Deficits in reach-to-grasp movement caused by macular scotomas are greater in degree than those reported by others for real or artificial peripheral scotomas.

Visuomotor training improves stroke-related ipsilesional upper extremity impairments.

BACKGROUND: Unilateral middle cerebral artery infarction has been reported to impair bilateral hand grasp. METHODS: Individuals (5 males and 5 females; age 33-86 years) with chronic unilateral middle cerebral artery stroke (4 right lesions and 6 left lesions) repeatedly lifted a 260-g object. Participants were then trained to lift the object using visuomotor feedback via an oscilloscope that displayed their actual grip force (GF) and a target GF, which roughly matched the physical properties of the object. RESULTS: The subjects failed to accurately modulate the predictive GF when relying on somatosensory information from the previous lifts. Instead, for all the lifts, they programmed excessive GF equivalent to the force used for the first lift. The predictive GF was lowered for lifts following the removal of the visual feedback. The mean difference in predictive GF between the lifts before and after visual training was significant (4.35 +/- 0.027 N; P

Aerobic exercise improves cognition and motor function poststroke.

BACKGROUND: Cognitive deficits impede stroke recovery. Aerobic exercise (AEX) improves cognitive executive function (EF) processes in healthy individuals, although the learning benefits after stroke are unknown. OBJECTIVE: To understand AEX-induced improvements in EF, motor learning, and mobility poststroke. METHODS: Following cardiorespiratory testing, 38 chronic stroke survivors were randomized to 2 different groups that exercised 3 times a week (45-minute sessions) for 8 weeks. The AEX group (n = 19; 9 women; 10 men; 64.10 +/- 12.30 years) performed progressive resistive stationary bicycle training at 70% maximal heart rate, whereas the Stretching Exercise (SE) group (n = 19; 12 women; 7 men; 58.96 +/- 14.68 years) performed stretches at home. Between-group comparisons were performed on the change in performance at "Post" and "Retention" (8 weeks later) for neuropsychological and motor function measures. RESULTS: VO(2)max significantly improved at Post with AEX (P = .04). AEX also improved motor learning in the less-affected hand, with large effect sizes (Cohen's d calculation). Specifically, AEX significantly improved information processing speed on the serial reaction time task (SRTT; ie, "procedural motor learning") compared with the SE group at Post (P = .024), but not at Retention. Also, at Post (P = .038), AEX significantly improved predictive force accuracy for a precision grip task requiring attention and conditional motor learning of visual cues. Ambulation and sit-to-stand transfers were significantly faster in the AEX group at Post (P = .038), with balance control significantly improved at Retention (P = .041). EF measurements were not significantly different for the AEX group. CONCLUSION: AEX improved mobility and selected cognitive domains related to motor learning, which enhances sensorimotor control after stroke.

A novel device to measure power grip forces in squirrel monkeys.

Understanding the neural bases for grip force behaviors in both normal and neurologically impaired animals is imperative prior to improving treatments and therapeutic approaches. The present paper describes a novel device for the assessment of power grip forces in squirrel monkeys. The control of grasping and object manipulation represents a vital aspect of daily living by allowing the performance of a wide variety of complex hand movements. However, following neurological injury such as stroke, these grasping behaviors are often severely affected, resulting in persistent impairments in strength, grip force modulation and kinematic hand control. While there is a significant clinical focus on rehabilitative strategies to address these issues, there exists the need for translational animal models. In the study presented here, we describe a simple grip force device designed for use in non-human primates, which provides detailed quantitative information regarding distal grip force dynamics. Adult squirrel monkeys were trained to exceed a specific grip force threshold, which was rewarded with a food pellet. One of these subjects then received an infarct of the M1 hand representation area. Results suggest that the device provides detailed and reliable information on grip behaviors in healthy monkeys and can detect deficits in grip dynamics in monkeys with cortical lesions (significantly longer release times). Understanding the physiological and neuroanatomical aspects of grasping function following neurological injury may lead to more effective rehabilitative interventions.

Retinal image location of hand, fingers, and objects during manual tasks.

PURPOSE: A new method was developed using the scanning laser ophthalmoscope (SLO) to investigate the effects of central visual loss on eye-hand coordination in manual tasks. Using the SLO, the retinal positions of the hand, fingers, and objects are imaged and recorded while a subject performs a manual task. METHOD: A video camera images the subject's hand and objects to be manipulated in the SLO laser-beam raster, producing a video image of a subject's hand, fingers, and objects on the subject's retina while the objects are manipulated. A subject with bilateral central scotomas and an age-matched control subject with normal vision traced an ellipse with the index finger, tapped four disks in sequence, and carried out a pattern duplication task with pegs. Retinal positions of the fovea or preferred retinal locus (PRL), fingers, and objects were measured from digitized SLO images. RESULTS: In all tasks, the fovea or PRL was directed to an object or position before the fingers arrived. This lead time was much greater for the scotoma subject than the control subject ( approximately 1400 vs. approximately 400 ms, respectively). The scotoma subject was much less accurate in placing the PRL and fingers on objects and required substantially more time for task completion than the control subject. CONCLUSIONS: The coordination of foveal fixation and finger placement found with the SLO method was similar to that found by others using eyetracking techniques with visually normal subjects. The presence of a central scotoma and use of a PRL caused marked deterioration in the quality of this coordination. Unlike eyetracking methods, the SLO technique does not require calibration because the positions of the fingers and objects are directly observable on the retina. This method could be useful in studying eye-hand coordination of individuals with scotomas that affect foveal vision.

Between-day reliability of upper extremity H-reflexes.

H-reflexes are useful for evaluating the group Ia monosynaptic reflex excitability in the lower and upper extremities (UEs). However, there is no established between-day protocol for measuring H-reflex excitability in the UE extensor carpi radialis longus (ECRL). The purpose of this study was to develop a reliable protocol to measure the H-reflex excitability between-days for the ECRL, and the antagonist muscle, the flexor carpi radialis (FCR). H-reflex recruitment curves were recorded from eight healthy young subjects over 3 consecutive days in both muscles. Variables associated with the H-reflex excitability were measured: (a) maximum amplitude (Hmax); (b) gain (HGN); (c) threshold (HTH, visHTH, and sdHTH). All variables were normalized with respect to the M-wave. Within individual muscles, there were no statistically significant differences between-days for the group (p>0.05) and variables showed fair to good reliability (ICC=0.57-0.99). This method of reliably measuring H-reflex excitability within UE muscles will be useful for investigating the effects of pathology and rehabilitation on monosynaptic reflexes.

Neuromuscular electrical stimulation improves severe hand dysfunction for individuals with chronic stroke: a pilot study.

Restoring hand function is difficult post-stroke. We sought to determine if applying neuromuscular electrical stimulation (NMES) was beneficial for reducing severe hand impairments. Subjects with chronic stroke (N=8; 3 Fe, 5 M; 58.3 +/- 6.9 y/o) received 10 sessions of NMES using two different methods applied in a counterbalanced order. In one intervention, we applied NMES (active) in a novel fashion using multiple stimulators on the forearm flexors and extensors to assist subjects with grasping and releasing a tennis ball. In the other intervention, the NMES ('passive') stimulated repeated wrist extension and flexion. Motor performance was assessed prior to and immediately following the interventions and at retention. Upper extremity (UE) Fugl-Myer scores significantly improved (p < 0.002) immediately following either intervention. Significant improvement was also observed in the Modified Ashworth Spasticity Scale (MASS) (p < 0.03), immediately following intervention, primarily due to the NMESpassive treatment (p < 0.034). Subjects performed grasping tasks significantly faster (p < 0.0433) following interventions, with performance speeds on dexterous manipulation increasing approximately 10% for NMESactive immediately following intervention, compared to only 0.1% improvement following NMESpassive. Generally, improvements in motor speed remained 10 days following NMESactive intervention, although slightly diminished. In conclusion, severe hand impairment was reduced after a short duration of NMES therapy in this pilot data set for individuals with chronic stroke. NMES-assisted grasping trended towards greater functional benefit than traditional NMES-activation of wrist flexors/extensors.

Impaired grip force modulation in the ipsilesional hand after unilateral middle cerebral artery stroke.

Understanding grasping control after stroke is important for relearning motor skills. The authors examined 10 individuals (5 males; 5 females; ages 32-86) with chronic unilateral middle cerebral artery (MCA) stroke (4 right lesions; 6 left lesions) when lifting a novel test object using skilled precision grip with their ipsilesional ("unaffected") hand compared to healthy controls (n = 14; 6 males; 8 females; ages 19-86). All subjects possessed normal range of motion, cutaneous sensation, and proprioception in the hand tested and had no apraxia or cognitive deficits. Subjects lifted the object 10 times at each object weight (260 g, 500 g, 780 g) using a moderately paced self-selected lifting speed. The normal horizontal ("grip") force and vertical tangential ("lift") force were separately measured at the thumb and index finger. Regardless of the object weight or stroke location, the stroke group generated greater grip forces at liftoff of the object (> or =39%; P < or = 0.05) and across the dynamic (P < or = 0.05) and static portions (P < or = 0.05) of the lifts compared to the healthy group. Peak lift forces were equivalent between groups, suggesting accurate load force information processing occurred. These results warrant further investigation of altered sensorimotor processing or compensatory biomechanical strategies that may lead to inaccurate grip force execution after strokes.

Dissociation of sensorimotor deficits after rostral versus caudal lesions in the primary motor cortex hand representation.

Primary motor cortex (M1) has traditionally been considered a motor structure. Although neurophysiologic studies have demonstrated that M1 is also influenced by somatosensory inputs (cutaneous and proprioceptive), the behavioral significance of these inputs has yet to be fully defined in primates. The present study describes differential sensory-related deficits after small ischemic lesions in either the rostral or caudal subregion of the M1 hand area in a nonhuman primate. Squirrel monkeys retrieved food pellets out of different sized wells drilled into a Plexiglas board. Before the lesion, monkeys retrieved pellets by directing the hand to the well, inserting fingers directly into it, and extracting the pellet. After a lesion to the rostral portion of M1, monkeys frequently failed to direct the hand accurately to the well. Instead, fingers contacted the surface of the board outside the well before entering the well. These aiming errors are consistent with both the large amount of proximal motor outputs and the predominant proprioceptive inputs of rostral M1. Overall, these aiming errors are suggestive of dysfunctional processing of proprioceptive information or the failure to integrate proprioceptive information with motor commands. In contrast, after a lesion to the caudal portion of M1, monkeys frequently examined their palm visually for the presence of the pellet after an attempted retrieval. These errors are consistent with both the large amount of distal motor outputs and the predominant cutaneous inputs of caudal M1. Thus these errors are suggestive of a deficit in processing of cutaneous information or the failure to integrate cutaneous information with motor commands. Rostral and caudal M1 lesions result in different deficits in sensory-dependent motor control that appear to correlate with broad segregation of motor outputs and previously described sensory inputs of M1.

Can internal models of objects be utilized for different prehension tasks?

We examined if object information obtained during one prehension task is used to produce fingertip forces for handling the same object in a different prehension task. Our observations address the task specificity of the internal models presumed to issue commands for grasping and transporting objects. Two groups participated in a 2-day experiment in which they lifted a novel object (230 g; 1.2 g/cm3). On Day One, the high force group (HFG) lifted the object by applying 10 N of grip force prior to applying vertical lift force. This disrupted the usual coordination of grip and lift forces and represented a higher grip force than necessary. The self-selected force group (SSFG) lifted the object on Day One with no instructions regarding their grip or lift forces. They first generated grip forces of 5.8 N, which decreased to 2.6 N by the 10th lift. Four hours later, they lifted the same object in the manner of the HFG. On Day Two, both groups lifted the same object "naturally and comfortably" with the opposite hand. The SSFG began Day Two using a grip force of 2.5 N, consistent with the acquisition of an accurate object representation during Day One. The HFG began Day Two using accurately scaled lift forces, but produced grip forces that virtually replicated those of the SSFG on Day One. We concur with recent suggestions that separate, independently adapted internal models produce grip and lift commands. The object representation that scaled lift force was not available to scale grip force. Furthermore, the concept of a general-purpose object representation that is available across prehension tasks was not supported.

Distributing vertical forces between the digits during gripping and lifting: the effects of rotating the hand versus rotating the object.

During pinch grip we partition the vertical tangential forces at the digits according to the friction at the grip surfaces, and the mass distribution of the object. However, we cannot predictively partition the vertical forces to adjust to new frictional conditions after viewing a 180-deg rotation of an object with different textures at each grip surface. Hence, the processes that lead to predictive force partitioning may not access object representations, thereby suggesting that these processes are digit-specific. If this is true, then we should fail to predictively partition our fingertip forces when we rotate our hand. We tested this prediction by comparing the effects of object rotation with hand rotation for repeated lifts of an object that had one slippery grip surface and one rough grip surface. Subjects did not predictively redistribute the vertical tangential forces upon grasping the rotated object. Following object rotation, the vertical tangential force trajectories during the first 100 ms after contact indicated that 12/15 subjects failed to anticipate the reversed digit-friction relationships. All subjects appropriately partitioned the vertical tangential forces between the digits by the second lift after object rotation, confirming previous reports that sensory signals update the memory associated with lifting the object. In contrast, after hand rotation, 13/15 subjects anticipated the new digit-friction relationships and upon grasping the object immediately generated a steep rise in the vertical force trajectory at the rough surface. They also delayed the initial rise in vertical tangential force at the digit encountering the low-friction surface by approximately 65 ms. Thus, anticipatory partitioning of vertical fingertip forces is not strictly digit-specific. Internally driven motor plans can access the relevant memories or internal models for predictively partitioning the vertical tangential forces. It is not clear if this process involves rotating internal representations of fingertip force directly, or if the forces are derived after internally rotating a representation of the object. In contrast to the robust effects of vision on reach kinematics, or on wrist and finger configuration, visual signals about object rotation and orientation apparently do not influence vertical tangential fingertip forces.

Post-infarct cortical plasticity and behavioral recovery using concurrent cortical stimulation and rehabilitative training: a feasibility study in primates.

Stroke is often characterized by incomplete recovery and chronic motor impairments. A nonhuman primate model of cortical ischemia was used to evaluate the feasibility of using device-assisted cortical stimulation combined with rehabilitative training to enhance behavioral recovery and cortical plasticity. Following pre-infarct training on a unimanual motor task, maps of movement representations in primary motor cortex were derived. Then, an ischemic infarct was produced which destroyed the hand representation. Several weeks later, a second cortical map was derived to guide implantation of a surface electrode over peri-infarct motor cortex. After several months of spontaneous recovery, monkeys underwent subthreshold electrical stimulation combined with rehabilitative training for several weeks. Post-therapy behavioral performance was tracked for several additional months. A third cortical map was derived several weeks post-therapy to examine changes in motor representations. Monkeys showed significant improvements in motor performance (success, speed, and efficiency) following therapy, which persisted for several months. Cortical mapping revealed large-scale emergence of new hand representations in peri-infarct motor cortex, primarily in cortical tissue underlying the electrode. Results support the feasibility of using a therapy approach combining peri-infarct electrical stimulation with rehabilitative training to alleviate chronic motor deficits and promote recovery from cortical ischemic injury.

Sensorimotor memory for fingertip forces: evidence for a task-independent motor memory.

When repetitively lifting an object with randomly varying mechanical properties, the fingertip forces reflect the previous lift. We examined the specificity of this "sensorimotor memory" by observing the effects of an isolated pinch on the subsequent lift of a known object. In this case, the pinch force was unrelated to the fingertip forces necessary to grip the object efficiently. The peak grip force used to lift the test object (4 N weight) depended on the preceding task. Compared with repetitively lifting the 4 N test object, the peak grip force was 2 N greater when a lift of the same object was preceded by a lift in which a hidden mass was attached to the object to increase the weight to 8 N. This 2 N increase in grip force also occurred when subjects lifted the 4 N test object after pinching a force transducer with a force of 8 N. Thus, similar grip forces were stored in sensorimotor memory for both tasks, and reflected subjects' use of 7.9 +/- 1.1 N to lift the 8 N object. Similar effects occurred when the preceding pinch or lift was performed with the opposite hand. The peak lift force was unaffected by the isolated pinch, suggesting that a generalized increase in fingertip and limb forces did not occur. We conclude that the sensorimotor memory is not specific for lifting an object. It is doubtful that this particular memory stores the physical properties of objects or reflects a forward internal model for predictively controlling fingertip forces.