Abnormalities in skilled reaching movements are improved by peripheral anesthetization of the less-affected forelimb after sensorimotor cortical infarcts in rats

Changes in ipsilesional hand motor function differ after unilateral injury to frontal versus frontoparietal cortices in Macaca mulatta

We tested the hypothesis that injury to frontoparietal sensorimotor areas causes greater initial impairments in performance and poorer recovery of ipsilesional dexterous hand/finger movements than lesions limited to frontal motor areas in rhesus monkeys. Reaching and grasping/manipulation of small targets with the ipsilesional hand were assessed for 6-12 months post-injury using two motor tests. Initial post-lesion motor skill and long-term recovery of motor skill were compared in two groups of monkeys: (1) F2 group-five cases with lesions of arm areas of primary motor cortex (M1) and lateral premotor cortex (LPMC) and (2) F2P2 group-five cases with F2 lesions + lesions of arm areas of primary somatosensory cortex and the anterior portion of area 5. Initial post-lesion reach and manipulation skills were similar to or better than pre-lesion skills in most F2 lesion cases in a difficult fine motor task but worse than pre-lesion skill in most F2P2 lesion cases in all tasks. Subsequently, reaching and manipulation skills improved over the post-lesion period to higher than pre-lesion skills in both groups, but improvements were greater in the F2 lesion group, perhaps due to additional task practice and greater ipsilesional limb use for daily activities. Poorer and slower post-lesion improvement of ipsilesional upper limb motor skill in the F2P2 cases may be due to impaired somatosensory processing. The persistent ipsilesional upper limb motor deficits frequently observed in humans after stroke are probably caused by greater subcortical white and gray matter damage than in the localized surgical injuries studied here.

Refinement of learned skilled movement representation in motor cortex deep output layer

The mechanisms underlying the emergence of learned motor skill representation in primary motor cortex (M1) are not well understood. Specifically, how motor representation in the deep output layer 5b (L5b) is shaped by motor learning remains virtually unknown. In rats undergoing motor skill training, we detect a subpopulation of task-recruited L5b neurons that not only become more movement-encoding, but their activities are also more structured and temporally aligned to motor execution with a timescale of refinement in tens-of-milliseconds. Field potentials evoked at L5b in vivo exhibit persistent long-term potentiation (LTP) that parallels motor performance. Intracortical dopamine denervation impairs motor learning, and disrupts the LTP profile as well as the emergent neurodynamical properties of task-recruited L5b neurons. Thus, dopamine-dependent recruitment of L5b neuronal ensembles via synaptic reorganization may allow the motor cortex to generate more temporally structured, movement-encoding output signal from M1 to downstream circuitry that drives increased uniformity and precision of movement during motor learning.

Motor compensation and its effects on neural reorganization after stroke

Stroke instigates a dynamic process of repair and remodelling of remaining neural circuits, and this process is shaped by behavioural experiences. The onset of motor disability simultaneously creates a powerful incentive to develop new, compensatory ways of performing daily activities. Compensatory movement strategies that are developed in response to motor impairments can be a dominant force in shaping post-stroke neural remodelling responses and can have mixed effects on functional outcome. The possibility of selectively harnessing the effects of compensatory behaviour on neural reorganization is still an insufficiently explored route for optimizing functional outcome after stroke.

Enduring Poststroke Motor Functional Improvements by a Well-Timed Combination of Motor Rehabilitative Training and Cortical Stimulation in Rats

BACKGROUND

In animal stroke models, peri-infarct cortical stimulation (CS) combined with rehabilitative reach training (RT) enhances motor functional outcome and cortical reorganization, compared with RT alone. It was unknown whether the effects of CS + RT (a) persist long after treatment, (b) can be enhanced by forcing greater use of the paretic limb, and (C) vary with treatment onset time.

OBJECTIVE

To test the endurance, time sensitivity, and the potential for augmentation by forced forelimb use of CS + RT treatment effects following ischemic stroke.

METHODS

Adult rats that were proficient in skilled reaching received unilateral ischemic motor cortical lesions. RT was delivered for 3 weeks alone or concurrently with 100-Hz cathodal epidural CS, delivered at 50% of movement thresholds. In study 1, this treatment was initiated at 14 days postinfarct, with some subgroups receiving an overlapping period of continuous constraint of the nonparetic forelimb to force use of the paretic limb. The function of the paretic limb was assessed weekly for 9 to 10 months posttreatment. In study 2, rats underwent CS, RT, and the combination during the chronic postinfarct period.

RESULTS

Early onset CS + RT resulted in greater functional improvements than RT alone. The CS-related gains persisted for 9 to 10 months posttreatment and were not significantly influenced by forced use of the paretic limb. When treatment onset was delayed until 3 months post-infarct, RT alone improved function, but CS + RT was no more effective than RT alone.

CONCLUSION

CS can enhance the persistence, as well as the magnitude of RT-driven functional improvements, but its effectiveness in doing so may vary with time postinfarct.

Mirror therapy enhances upper extremity motor recovery in stroke patients

The purpose of this study was to evaluate the effects of mirror therapy program in addition with physical therapy methods on upper limb recovery in patients with subacute ischemic stroke. 15 subjects followed a comprehensive rehabilitative treatment, 8 subjects received only control therapy (CT) and 7 subjects received mirror therapy (MT) for 30 min every day, five times a week, for 6 weeks in addition to the conventional therapy. Brunnstrom stages, Fugl-Meyer Assessment (upper extremity), the Ashworth Scale, and Bhakta Test (finger flexion scale) were used to assess changes in upper limb motor recovery and motor function after intervention. After 6 weeks of treatment, patients in both groups showed significant improvements in the variables measured. Patients who received MT showed greater improvements compared to the CT group. The MT treatment results included: improvement of motor functions, manual skills and activities of daily living. The best results were obtained when the treatment was started soon after the stroke. MT is an easy and low-cost method to improve motor recovery of the upper limb.

Training Intensity Affects Motor Rehabilitation Efficacy Following Unilateral Ischemic Insult of the Sensorimotor Cortex in C57BL/6 Mice

BACKGROUND

Motor rehabilitative training improves behavioral functionality and promotes beneficial neural reorganization following stroke but is often insufficient to normalize function. Rodent studies have relied on skilled reaching tasks to model motor rehabilitation and explore factors contributing to its efficacy. It has been found that greater training intensity (sessions/day) and duration (training days) facilitates motor skill learning in intact animals. Whether rehabilitative training efficacy varies with intensity following stroke is unclear.

METHODS

Mice were trained preoperatively on a skilled reaching task. Following focal ischemic lesions, mice received rehabilitative training either twice daily (high intensity [HI]), once daily (low intensity [LI]), or not at all (control) to determine the effects of rehabilitative training intensity on skilled motor performance.

RESULTS

Within 7 days, the HI-trained mice achieved preischemic levels of performance. Mice receiving LI training eventually reached similar performance levels but required a greater quantity of training. Training intensity did not consistently affect the maintenance of performance gains, which were partially lost over time in both groups.

DISCUSSION

These data indicate that increased training intensity increases the rate of functional improvements per time and per training session following ischemic insult. Thus, training intensity is an important variable to consider in efforts to optimize rehabilitation efficacy.

Compensatory limb use and behavioral assessment of motor skill learning following sensorimotor cortex injury in a mouse model of ischemic stroke

Mouse models have become increasingly popular in the field of behavioral neuroscience, and specifically in studies of experimental stroke. As models advance, it is important to develop sensitive behavioral measures specific to the mouse. The present protocol describes a skilled motor task for use in mouse models of stroke. The Pasta Matrix Reaching Task functions as a versatile and sensitive behavioral assay that permits experimenters to collect accurate outcome data and manipulate limb use to mimic human clinical phenomena including compensatory strategies (i.e., learned non-use) and focused rehabilitative training. When combined with neuroanatomical tools, this task also permits researchers to explore the mechanisms that support behavioral recovery of function (or lack thereof) following stroke. The task is both simple and affordable to set up and conduct, offering a variety of training and testing options for numerous research questions concerning functional outcome following injury. Though the task has been applied to mouse models of stroke, it may also be beneficial in studies of functional outcome in other upper extremity injury models.

The bradykinesia assessment task: an automated method to measure forelimb speed in rodents

Bradykinesia in upper extremities is associated with a wide variety of motor disorders; however, there are few tasks that assay forelimb movement speed in rodent models. This study describes the bradykinesia assessment task, a novel method to quantitatively measure forelimb speed in rats. Rats were trained to reach out through a narrow slot in the cage and rapidly press a lever twice within a predefined time window to receive a food reward. The task provides measurement of multiple parameters of forelimb function, including inter-press interval, number of presses per trial, and success rate. The bradykinesia assessment task represents a significant advancement in evaluating bradykinesia in rat models because it directly measures forelimb speed. The task is fully automated, so a single experimenter can test multiple animals simultaneously with typically in excess of 300 trials each per day, resulting in high statistical power. Several parameters of the task can be modified to adjust difficulty, which permits application to a broad spectrum of motor dysfunction models. Here we show that two distinct models of brain damage, ischemic lesions of primary motor cortex and hemorrhagic lesions of the dorsolateral striatum, cause impairment in all facets of performance measured by the task. The bradykinesia assessment task provides insight into bradykinesia and motor dysfunction in multiple disease models and may be useful in assessing therapies that aim to improve forelimb function following brain damage.

The isometric pull task: a novel automated method for quantifying forelimb force generation in rats

Reach-to-grasp tasks are commonly used to assess forelimb function in rodent models. While these tasks have been useful for investigating several facets of forelimb function, they are typically labor-intensive and do not directly quantify physiological parameters. Here we describe the isometric pull task, a novel method to measure forelimb strength and function in rats. Animals were trained to reach outside the cage, grasp a handle attached to a stationary force transducer, and pull with a predetermined amount of force to receive a food reward. This task provides quantitative data on operant forelimb force generation. Multiple parameters can be measured with a high degree of accuracy, including force, success rate, pull attempts, and latency to maximal force. The task is fully automated, allowing a single experimenter to test multiple animals simultaneously with usually more than 300 trials per day, providing more statistical power than most other forelimb motor tasks. We demonstrate that an ischemic lesion in primary motor cortex yields robust deficits in all forelimb function parameters measured with this method. The isometric pull task is a significant advance in operant conditioning systems designed to automate the measurement of multiple facets of forelimb function and assess deficits in rodent models of brain damage and motor dysfunction.

Experience-dependent neural plasticity in the adult damaged brain

Behavioral experience is at work modifying the structure and function of the brain throughout the lifespan, but it has a particularly dramatic influence after brain injury. This review summarizes recent findings on the role of experience in reorganizing the adult damaged brain, with a focus on findings from rodent stroke models of chronic upper extremity (hand and arm) impairments. A prolonged and widespread process of repair and reorganization of surviving neural circuits is instigated by injury to the adult brain. When experience impacts these same neural circuits, it interacts with degenerative and regenerative cascades to shape neural reorganization and functional outcome. This is evident in the cortical plasticity resulting from compensatory reliance on the "good" forelimb in rats with unilateral sensorimotor cortical infarcts. Behavioral interventions (e.g., rehabilitative training) can drive functionally beneficial neural reorganization in the injured hemisphere. However, experience can have both behaviorally beneficial and detrimental effects. The interactions between experience-dependent and injury-induced neural plasticity are complex, time-dependent, and varied with age and other factors. A better understanding of these interactions is needed to understand how to optimize brain remodeling and functional outcome.

LEARNING OUTCOMES

Readers will be able to describe (a) experience effects that are maladaptive for behavioral outcome after brain damage, (b) manipulations of experience that drive functionally beneficial neural plasticity, and (c) reasons why rehabilitative training effects can be expected to vary with age, training duration and timing.

Volumetric effects of motor cortex injury on recovery of ipsilesional dexterous movements

Damage to the motor cortex of one hemisphere has classically been associated with contralateral upper limb paresis, but recent patient studies have identified deficits in both upper limbs. In non-human primates, we tested the hypothesis that the severity of ipsilesional upper limb motor impairment in the early post-injury phase depends on the volume of gray and white matter damage of the motor areas of the frontal lobe. We also postulated that substantial recovery would accompany minimal task practice and that ipsilesional limb recovery would be correlated with recovery of the contralesional limb. Gross (reaching) and fine hand motor functions were assessed for 3-12 months post-injury using two motor tests. Volumes of white and gray matter lesions were assessed using quantitative histology. Early changes in post-lesion motor performance were inversely correlated with white matter lesion volume indicating that larger lesions produced greater decreases in ipsilesional hand movement control. All monkeys showed improvements in ipsilesional hand motor skill during the post-lesion period, with reaching skill improvements being positively correlated with total lesion volume indicating that larger lesions were associated with greater ipsilesional motor skill recovery. We suggest that reduced trans-callosal inhibition from the lesioned hemisphere may play a role in the observed skill improvements. Our findings show that significant ipsilesional hand motor recovery is likely to accompany injury limited to frontal motor areas. In humans, more pronounced ipsilesional motor deficits that invariably develop after stroke may, in part, be a consequence of more extensive subcortical white and gray matter damage.

Breeder and batch-dependent variability in the acquisition and performance of a motor skill in adult Long-Evans rats

Reaching tasks are popular tools for investigating the neural mechanisms of motor skill learning and recovery from brain damage in rodents, but there is considerable unexplained variability across studies using these tasks. We investigated whether breeder, batch effects, experimenter, time of year, weight and other factors contribute to differences in the acquisition and performance of a skilled reaching task, the single pellet retrieval task, in adult male Long-Evans hooded rats. First, we retrospectively analyzed task acquisition and performance in rats from different breeding colonies that were used in several studies spanning a 3 year period in our laboratory. Second, we compared reaching variables in age-matched rats from different breeders that were trained together as a batch by the same experimenters. All rats had received daily training on the reaching task until they reached a criterion of successful reaches per attempt. We found significant breeder-dependent differences in learning rate and final performance level. This was found even when age-matched rats from different breeders were trained together by the same experimenters. There was also significant batch-to-batch variability within rats from the same breeder trained by the same experimenter. Other factors, including weight, paw preference and the experimenter, were not as strong or consistent in their contributions to differences across studies. The breeder and batch effects found within the same rat strain may reflect genetic and environmental influences on the neural substrates of motor skill learning. This is an important consideration when comparing baseline performance across studies and for controlling variability within studies.

The "good" limb makes the "bad" limb worse: experience-dependent interhemispheric disruption of functional outcome after cortical infarcts in rats

Following stroke-like lesions to the sensorimotor cortex in rats, experience with the ipsi-to-lesion (ipsilesional), "nonparetic", forelimb worsens deficits in the contralesional, "paretic", forelimb. We tested whether the maladaptive effects of experience with the nonparetic limb are mediated through callosal connections and the contralesional sensorimotor cortex. Adult male rats with proficiency in skilled reaching with their dominant (for reaching) forelimb received ischemic bilateral sensorimotor cortex lesions, or unilateral lesions, with or without callosal transections. After assessing dominant forelimb function (the paretic forelimb in rats with unilateral lesions), animals were trained with their nonparetic/nondominant forelimb or underwent control procedures for 15 days. Animals were then tested with their paretic/dominant forelimb. In animals with unilateral lesions only, nonparetic forelimb training worsened subsequent performance with the paretic forelimb, as found previously. This effect was not found in animals with both callosal transections and unilateral lesions. After bilateral lesions, training the nondominant limb did not worsen function of the dominant limb compared with controls. Thus, the maladaptive effects of training the nonparetic limb on paretic forelimb function depend upon the contralesional cortex and transcallosal projections. This suggests that this experience-dependent disruption of functional recovery is mediated through interhemispheric connections of the sensorimotor cortex.

Sensorimotor behavioral effects of endothelin-1 induced small cortical infarcts in C57BL/6 mice

Mouse models have not paralleled rat models of stroke in advances in sensitive, species appropriate measures of neurological and behavioral recovery. Most available tests of mouse sensorimotor function are adaptations of those originally developed in rats and may not be as sensitive in detecting behavioral deficits after small cortical lesions in mice. Our purpose was to test the use of a vasoconstricting peptide, endothelin-1 (ET-1), to produce focal infarcts of the mouse sensorimotor cortex and to establish a behavioral test battery sensitive to resulting sensorimotor deficits. Young adult (3-5-month-old) male C57BL/6 mice received intracortical infusions of ET-1 that produced unilateral lesions of the forelimb region of the sensorimotor cortex, intracortical infusions of sterile saline, or sham surgeries. Pre-operatively and at various time points over 3 weeks post-surgery, they were administered a test battery that included measures of sensorimotor asymmetry (Corner and Bilateral Tactile Stimulation Tests), coordinated forepaw use (Cylinder and Ladder Rung Tests), and dexterous forepaw function (Pasta Matrix Reaching Test). ET-1 infusions resulted in consistently placed, focal cortical infarcts and forelimb impairments as measured with the Ladder Rung, Bilateral Tactile Stimulation, and Pasta Matrix Reaching Tests. On the Bilateral Tactile Stimulation and Pasta Matrix Reaching Tests, impairments persisted throughout the time span of observation (26 days). These results support ET-1 as a viable option for creating small, reproducible lesions of anatomical subregions in the mouse neocortex that result in lasting functional impairments in the forelimb, as observed with sufficiently sensitive measures.

Remodeling the brain with behavioral experience after stroke

BACKGROUND AND PURPOSE

Behavioral experience can drive brain plasticity, but we lack sufficient knowledge to optimize its therapeutic use after stroke.

METHODS

We outline recent findings from rodent models of cortical stroke of how experiences interact with postinjury events to influence synaptic connectivity and functional outcome. We focus on upper extremity function.

RESULTS

After unilateral cortical infarcts, behavioral experiences shape neuronal structure and activity in both hemispheres. Experiences that matter include interventions such as skill training and constraint-like therapy as well as unguided behaviors such as learned nonuse and behavioral compensation. Lateralized behaviors have bihemispheric influences. Ischemic injury can alter the sensitivity of remaining neocortical neurons to behavioral change and this can have positive and negative functional effects.

CONCLUSIONS

Because experience is ongoing in stroke survivors, a better understanding of its interaction with brain reorganization is needed so that it can be manipulated to improve function and prevent its worsening.

Experience--a double edged sword for restorative neural plasticity after brain damage

During the time period following damage, the brain undergoes widespread reorganizational processes. Manipulations of behavioral experience can be potent therapeutic interventions for shaping this reorganization and enhancing long-term functional outcome. Recovery of function is a major concern for survivors of central nervous system damage and management of post-injury rehabilitation is increasingly becoming a topic of chief importance. Animal research, the focus of this review, suggests that, in the absence of behavioral manipulations, the brain is unlikely to realize its full potential for supporting function. However, experiences also have the capacity to be maladaptive for brain and behavioral function. From a treatment perspective, it may be unwise to adopt the canon of "first, do no harm" because maladaptive experiences include behaviors that individuals learn to do on their own. A better understanding of how behavioral experience interacts with brain reorganization could result in rehabilitative therapies, individually tailored and optimized for functional outcome.

Maladaptive effects of learning with the less-affected forelimb after focal cortical infarcts in rats

It is common following stroke to focus early rehabilitation efforts on developing compensatory use of the less-affected body side. Here we used a rat model of focal cortical infarct to examine how motor skill acquisition with the less-affected ("intact") forelimb influences sensorimotor function of the infarct-impaired forelimb and neural activity in peri-infarct cortex. Rats proficient in skilled reaching with one forelimb were given focal ischemic lesions in the contralateral sensorimotor cortex (SMC). Recovery in this forelimb was tested following a period of reach training focused on the intact forelimb or control procedures. Quantitative measures of the cumulatively expressed transcription factor, FosB/DeltaFosB, were used to assay intact forelimb training effects on neuronal activity in remaining SMC of the infarcted hemisphere. Intact forelimb training worsened behavioral recovery in the impaired forelimb following unilateral focal ischemia. Furthermore, it decreased neuronal FosB/DeltaFosB expression in layer II/III of peri-infarct SMC. These effects were not found in sham-operated rats trained sequentially with both forelimbs or in animals receiving bilateral forelimb training after unilateral infarcts. Thus, focused use of the intact forelimb has detrimental effects on recovery of impaired forelimb function following a focal ischemic injury and this is linked to reduced neuronal activation in remaining cortex. These results suggest that peri-infarct cortex becomes vulnerable to early post-stroke experience with the less-affected forelimb and that this experience may drive neural plasticity here in a direction that is maladaptive for functional outcome.

Rat Models of Upper Extremity Impairment in Stroke

Stroke remains the leading cause of adult disability, with upper extremity motor impairments being the most prominent functional deficit in surviving stroke victims. The development of animal models of upper extremity dysfunction after stroke has enabled investigators to examine the neural mechanisms underlying rehabilitation-dependent motor recovery as well as the efficacy of various adjuvant therapies for enhancing recovery. Much of this research has focused on rat models of forelimb motor function after experimentally induced ischemic or hemorrhagic stroke. This article provides a review of several different methods for inducing stroke, including devascularization, photothrombosis, chemical vasoconstriction, and hemorrhagia. We also describe a battery of sensorimotor tasks for assessing forelimb motor function after stroke. The tasks range from measures of gross motor performance to fine object manipulation and kinematic movement analysis, and we offer a comparison of the sensitivity for revealing motor deficits and the amount of time required to administer each motor test. In addition, we discuss several important methodological issues, including the importance of testing on multiple tasks to characterize the nature of the impairments, establishing stable baseline prestroke motor performance measures, dissociating the effects of acute versus chronic testing, and verifying lesion location and size. Finally, we outline general considerations for conducting research using rat models of stroke and the role that these models should play in guiding clinical trials.