The purpose of the present study was to determine the feasibility of using a common laboratory rat strain for locating cortical motor representations of the hindlimb reliably.
Intracortical Microstimulation (ICMS) techniques were used to derive detailed maps of the hindlimb motor representations in six adult Fischer-344 rats.
The organization of the hindlimb movement representation, while variable across individuals in topographic detail, displayed several commonalities. The hindlimb representation was positioned posterior to the forelimb motor representation and postero-lateral to the motor trunk representation. The areal extent of the hindlimb representation across the cortical surface averaged 2.00 +/− 0.50 mm2. Superimposing individual maps revealed an overlapping area measuring 0.35 mm2, indicating that the location of the hindlimb representation can be predicted reliably based on stereotactic coordinates. Across the sample of rats, the hindlimb representation was found 1.25–3.75 mm posterior to Bregma, with an average center location ~ 2.6 mm posterior to Bregma. Likewise, the hindlimb representation was found 1–3.25 mm lateral to the midline, with an average center location ~ 2 mm lateral to midline.
The location of the cortical hindlimb motor representation in Fischer-344 rats can be reliably located based on its stereotactic position posterior to Bregma and lateral to the longitudinal skull suture at midline. The ability to accurately predict the cortical localization of functional hindlimb territories in a rodent model is important, as such animal models are being used increasingly in the development of brain-computer interfaces for restoration of function after spinal cord injury.
Motor Cortex; Hindlimb; Fischer-344; Intracortical Microstimulation
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.
Grip force; power grip; monkey; stroke; hand; primates
Current research in brain computer interface (BCI) technology is advancing beyond preclinical studies, with trials beginning in human patients. To date, these trials have been carried out with several different types of recording interfaces. The success of these devices has varied widely, but different factors such as the level of invasiveness, timescale of recorded information, and ability to maintain stable functionality of the device over a long period of time all must be considered in addition to accuracy in decoding intent when assessing the most practical type of device moving forward. Here, we discuss various approaches to BCIs, distinguishing between devices focusing on control of operations extrinsic to the subject (e.g., prosthetic limbs, computer cursors) and those focusing on control of operations intrinsic to the brain (e.g., using stimulation or external feedback), including closed-loop or adaptive devices. In this discussion, we consider the current challenges facing the translation of various types of BCI technology to eventual human application.
brain-computer interface (BCI); microelectrodes; electrocorticography (ECoG); electroencephalography (EEG); closed-loop neuroprosthetic devices; neural prostheses
We investigated whether precision grasping of small objects between the index and thumb of the impaired hand recovers without forced use after surgically placed lesions to the hand/arm areas of M1 and M1 + lateral premotor cortex (LPMC) in two monkeys. The unilateral lesions were contralateral to the monkey's preferred hand, which was established in pre-lesion testing as the hand used most often to acquire raisins in a foraging board task in which the monkey was free to use either hand to acquire the treats. The lesions initially produced a clear paresis of the contralesional hand and use of only the ipsilesional hand to acquire raisins in the foraging board task. However, beginning about 3 weeks after the lesion the monkey spontaneously began using the impaired contralesional hand in the foraging board task and increased use of that hand over the next few tests. Moreover, the monkeys clearly used precision grasp to acquire the raisins in a similar manner to pre-lesion performances, although grasp durations were longer. Although the monkeys used the contralesional hand more often than the ipsilesional hand in some post-lesion testing sessions they did not recover to use the hand as often as in pre-lesion testing when the preferred hand was used almost exclusively. These findings suggest that recovery of fine hand/digit motor function after localized damage to the lateral frontal motor areas in rhesus monkeys does not require forced use of the impaired hand.
finger; grip; dexterity
The past 20 years have represented an important period in the development of principles underlying neuroplasticity, especially as they apply to recovery from neurological injury. It is now generally accepted that acquired brain injuries, such as occur in stroke or trauma, initiate a cascade of regenerative events that last for at least several weeks, if not months. Many investigators have pointed out striking parallels between post-injury plasticity and the molecular and cellular events that take place during normal brain development. As evidence for the principles and mechanisms underlying post-injury neuroplasticity has been gleaned from both animal models and human populations, novel approaches to therapeutic intervention have been proposed. One important theme has persisted as the sophistication of clinicians and scientists in their knowledge of neuroplasticity mechanisms has grown: behavioral experience is the most potent modulator of brain plasticity. While there is substantial evidence for this principle in normal, healthy brains, the injured brain is particularly malleable. Based on the quantity and quality of motor experience, the brain can be reshaped after injury in either adaptive or maladaptive ways. This paper reviews selected studies that have demonstrated the neurophysiological and neuroanatomical changes that are triggered by motor experience, by injury, and the interaction of these processes. In addition, recent studies using new and elegant techniques are providing novel perspectives on the events that take place in the injured brain, providing a real-time window into post-injury plasticity. These new approaches are likely to accelerate the pace of basic research, and provide a wealth of opportunities to translate basic principles into therapeutic methodologies.
motor cortex; stroke; traumatic brain injury; axonal sprouting; motor learning; recovery
It is generally assumed that proprioceptive feedback plays a crucial role in limb posture and movement. However, the role of afferent signals from extraocular muscles (EOM) in the control of eye movement has been a matter of continuous debate. These muscles have atypical sensory receptors in several species and it has been proposed that they are not supported by stretch reXexes. We recorded electromyographic activity of EOM during passive rotations of the eye in sedated rats and squirrel monkeys and observed typical stretch reXexes in these muscles. Results suggest that there is a similarity in the reXexive control of limb and eye movement, despite substantial differences in their biomechanics and sensory receptors. Like in some limb skeletal muscles, the stretch reflex in EOM in the investigated species might be mediated by other length-sensitive receptors, rather than muscle spindles.
Motor control; Sensorimotor integration; Eye movement; Proprioception; Electromyogram
We report the results of controlled cortical impact (CCI) centered on the caudal forelimb area (CFA) of rat motor cortex to determine the feasibility of examining cortical plasticity in a spared cortical motor area (rostral forelimb area, RFA). We compared the effects of three CCI parameter sets (groups CCI-1, CCI-2, and CCI-3) that differed in impactor surface shape, size, and location, on behavioral recovery and RFA structural and functional integrity. Forelimb deficits in the limb contralateral to the injury were evident in all three CCI groups assessed by skilled reach and footfault tasks that persisted throughout the 35-day post-CCI assessment period. Nissl-stained coronal sections revealed that the RFA was structurally intact. Intracortical microstimulation experiments conducted at 7 weeks post-CCI demonstrated that RFA was functionally viable. However, the size of the forelimb representation decreased significantly in CCI-1 compared to the control group. Subdivided into component movement categories, there was a significant group effect for proximal forelimb movements. The RFA area reduction and reorganization are discussed in relation to possible diaschisis, and to compensatory functional behavior, respectively. Also, an inverse correlation between the anterior extent of the lesion and the size of the RFA was identified and is discussed in relation to corticocortical connectivity. The results suggest that CCI can be applied to rat CFA while sparing RFA. This CCI model can contribute to our understanding of neural plasticity in premotor cortex as a substrate for functional motor recovery.
behavioral recovery; cortical plasticity; intracortical microstimulation; motor impairment; traumatic brain injury
Background and Purpose
Although myelin-associated neurite outgrowth disinhibitors have shown promise in restoring motor function after stroke, their interactive effects with motor training have rarely been investigated. The present study examined whether a combinatorial treatment (NEP 1–40+motor rehabilitation) is more effective than either treatment alone in promoting motor recovery after focal ischemic injury.
Adult rats were assigned to one of 3 treatment groups (infarct/NEP 1–40+motor training, infarct/NEP 1–40 only, infarct/motor training only) and 2 control groups (infarct/no treatment, intact/no treatment). A focal ischemic infarct was induced by microinjecting endothelin-1 into the motor cortex. Therapeutic treatments were initiated 1 week postinfarct and included intraventricular infusion of the pharmacological agent NEP 1–40 and motor training (skilled reach task). Behavioral assessments on skilled reach, foot fault, and cylinder tests were conducted before the infarct and for 5 weeks postinfarct.
Rats demonstrated significant forelimb impairment on skilled reach and foot fault tests after the infarct. Although all infarct groups improved over time, motor training alone and NEP 1–40 alone facilitated recovery on the skilled reach task at the end of treatment Weeks 2 and 4, respectively. However, only NEP 1–40 paired with motor training facilitated recovery after 1 week of treatment in addition to treatment at Weeks 2 and 4. Finally, only the NEP 1–40+motor training group maintained a performance level equivalent to that of the intact group over the entire period of posttreatment assessment.
This study suggests that behavioral training interacts with the effects of the axonal growth promoter, NEP 1–40, and may accelerate behavioral recovery after focal cortical ischemia.
cerebral infarct; motor cortex; rehabilitation; recovery; regeneration
Abnormal task-related activation in primary motor cortices (M1) has been consistently found in functional imaging studies of subcortical stroke. Whether the abnormal activations are associated with neuronal alterations in the same or homologous area is not known.
Our goal was to establish the relationships between M1 measures of motor task-related activation and a neuronal marker, N-acetylaspartate, in patients with severe to mild hemiparesis.
Eighteen survivors of an ischemic subcortical stroke (confirmed on T2-weighted images) at more than six months post-onset and sixteen age- and sex-matched right-handed healthy controls underwent functional MRI during a handgrip task (impaired hand in patients, dominant hand in controls) and proton magnetic resonance spectroscopy (1H-MRS) imaging. Spatial extent and magnitude of blood oxygen level-dependent response (or activation) and N-acetylaspartate levels were measured in each M1. Relationships between activation and N-acetylaspartate were determined.
Compared to controls, patients had greater extent of contralesional (ipsilateral to impaired hand, p<.001) activation, higher magnitude of activation and lower N-acetylaspartate in both ipsilesional (p=.008 and p<.001 respectively) and contralesional (p<.0001, p<.05) M1. There were significant negative correlations between extent of activation and N-acetylaspartate in each M1 (p=.02) and a trend between contralesional activation and ipsilesional N-acetylaspartate (p=.08) in patients but not in controls.
Our results suggest that greater neuronal recruitment could be a compensatory response to lower neuronal metabolism. Dual-modality imaging may be a powerful tool for investigating relationships between complementary data regarding post-stroke brain reorganization.
subcortical stroke; primary motor cortex; 1H-MRS; fMRI; functional-biochemistry relationship
Approximately 700,000 people in the United States have an ischemic stroke annually. Substantial research has tested therapies for the very early treatment of ischemic stroke but, to date, only intravenous thrombolysis and intra-arterial measures to restore perfusion have shown success. Despite a 15-year effort to increase the use of these therapies, only approximately 5% of patients with stroke are currently being treated. Although most patients with stroke have some neurological recovery, more than half of stroke survivors have residual impairments that lead to disability or long-term institutionalized care. Laboratory research has demonstrated several mechanisms that help the brain to recover after a stroke. New pharmacological and cell-based approaches that are known to promote brain plasticity are emerging from laboratory studies and may soon expand the window for stroke treatment to restore function. It is time to build on this knowledge and to translate the understanding of recovery after stroke into the clinical setting. Measures that might augment recovery should become a major focus of clinical research in stroke in the 21st century.
ischemic stroke; stroke recovery; rehabilitation
Although functional imaging and neurophysiological approaches reveal alterations in motor and premotor areas after stroke, insights into neurobiological events underlying these alterations are limited in human studies.
We tested whether cerebral metabolites related to neuronal and glial compartments are altered in the hand representation in bilateral motor and premotor areas and correlated with distal and proximal arm motor impairment in hemiparetic persons.
In twenty participants at >6 months post-onset of a subcortical ischemic stroke and sixteen age and sex-matched healthy controls, the concentrations of N-acetylaspartate and myoinositol were quantified by proton magnetic resonance spectroscopy (1H-MRS). Regions of interest, identified by functional MRI, included primary (M1), dorsal premotor (PMd), and supplementary (SMA) motor areas. Relationships between metabolite concentrations and distal (hand) and proximal (shoulder/elbow) motor impairment using Fugl-Meyer Upper Extremity (FMUE) subscores were explored.
N-acetylaspartate was lower in M1 (p=0.04) and SMA (p=0.004) and myo-inositol was higher in M1 (p=0.003) and PMd (p=0.03) in the injured (ipsilesional) hemisphere after stroke compared to the left hemisphere in controls. N-acetylaspartate in ipsilesional M1 was positively correlated with hand FMUE subscores (p=0.04). Significant positive correlations were also found between N-acetylaspartate in ipsilesional M1, PMd, and SMA and in contralesional M1 and shoulder/elbow FMUE subscores (p=0.02, 0.01, 0.02 and 0.02 respectively).
Our preliminary results demonstrated that 1H-MRS is a sensitive method to quantify relevant neuronal changes in spared motor cortex after stroke, and consequently increase our knowledge of the factors leading from these changes to arm motor impairment.
subcortical stroke; motor and premotor cortices; proton magnetic resonance spectroscopy; distal and proximal arm motor impairment
During recovery from a unilateral cortical stroke, spared cortical motor areas in the contralateral (intact) cerebral cortex are recruited. Pre-clinical studies have demonstrated that compensation with the less-impaired limb may have a detrimental inhibitory effect on the intact cortical hemisphere and could impede recovery of the more-impaired limb. However, evidence from detailed neurophysiological mapping studies in animal models is lacking.
The present study examines neurophysiological changes in the intact hemisphere of the rat following a unilateral ischemic infarct to cortical forelimb motor areas.
Eight rats were trained for two weeks on a reach and retrieval task prior to an ischemic infarct induced by the vasoconstrictor, endothelin-1 injected into the cortical grey matter encompassing the two forelimb motor representations, the caudal forelimb area (CFA) and the rostral forelimb area (RFA). Animals were randomly assigned to an Infarct/Training group (n=4) or an Infarct/No Training group (i.e., spontaneous recovery, n=4). After a five-week post-infarct period, motor areas of the intact hemisphere (CFA and RFA) were characterized using intracortical microstimulation techniques. The resulting maps of evoked movements were compared to maps derived from CFA and RFA in normal rats (Normal, n=5; Normal/Training, n=4).
Compared with the Normal/No Training group, CFA representations were significantly smaller in the Infarct/Training group but not in the Infarct/No Training group. No significant differences were found in RFA.
Repetitive training of the more-impaired forelimb during the post-infarct recovery period reduces the size of motor representations in the intact hemisphere.
Motor Rehabilitation; Interhemispheric Competition; ICMS; Motor Cortex; Ischemia
After cortical injury resulting from stroke, some recovery can occur and may involve spared areas of the cerebral cortex reorganizing to assume functions previously controlled by the damaged cortical areas. No studies have specifically assessed gene expression changes in remote neurons with axonal processes that terminate in the infarcted tissue, i.e., the subset of neurons most likely to be involved in regenerative processes. By physiologically identifying the primary motor area controlling forelimb function in adult rats (caudal forelimb area = CFA), and injecting a retrograde tract-tracer, we labeled neurons within the non-primary motor cortex (rostral forelimb area = RFA) that project to CFA. Then, 7 days after a CFA infarct (n = 6), we used laser capture microdissection techniques to harvest labeled neurons in RFA. Healthy, uninjured rats served as controls (n = 6). Biological interactions and functions of gene profiling were investigated by Affymetrix Microarray, and Ingenuity Pathway Analysis. A total of 143 up- and 128 down-regulated genes showed significant changes (fold change ≥1.3 and p <0.05). The canonical pathway, “Axonal Guidance Signaling,” was overrepresented (p value = 0.002). Significantly overrepresented functions included: branching of neurites, organization of cytoskeleton, dendritic growth and branching, organization of cytoplasm, guidance of neurites, development of cellular protrusions, density of dendritic spines, and shape change (p = 0.000151–0.0487). As previous studies have shown that spared motor areas are important in recovery following injury to the primary motor area, the results suggest that these gene expression changes in remote, interconnected neurons may underlie reorganization and recovery mechanisms.
Stroke; Ischemic infarct; Motor cortex; Plasticity; Gene expression
Whether functional changes of the non-primary motor areas, e.g., dorsal premotor (PMd) and supplementary motor (SMA) areas, after stroke, reflect reorganization phenomena or recruitment of a pre-existing motor network remains to be clarified. We hypothesized that cellular changes in these areas would be consistent with their involvement in post-stroke reorganization. Specifically, we expected that neuronal and glial compartments would be altered in radiologically normal-appearing, i.e., spared, PMd and SMA in patients with arm paresis. Twenty survivors of a single ischemic subcortical stroke and 16 age-matched healthy controls were included. At more than six months after stroke, metabolites related to neuronal and glial compartments: N-acetylaspartate, myo-inositol, and glutamate/glutamine, were quantified by proton magnetic resonance spectroscopy in PMd and SMA in both injured (ipsilesional) and un-injured (contralesional) hemispheres. Correlations between metabolites were also calculated. Finally, relationships between metabolite concentrations and arm motor impairment (total and proximal Fugl-Meyer Upper Extremity, FMUE, scores) were analyzed. Compared to controls, stroke survivors showed significantly higher ipsilesional PMd myo-inositol and lower SMA N-acetylaspartate. Significantly lower metabolite correlations were found between ipsilesional and contralesional SMA. Ipsilesional N-acetylaspartate was significantly related to proximal FMUE scores. This study provides evidence of abnormalities in metabolites, specific to neuronal and glial compartments, across spared non-primary motor areas. Ipsilesional alterations were related to proximal arm motor impairment. Our results suggest the involvement of these areas in post-stroke reorganization.
1H-MRS; Neuronal and glial compartments; Non-primary motor areas; Subcortical stroke
Substantial data have accumulated over the past decade indicating that the adult brain is capable of substantial structural and functional reorganization after stroke. While some limited recovery is known to occur spontaneously, especially within the first month post-stroke, there is currently significant optimism that new interventions based on the modulation of neuroplasticity mechanisms will provide greater functional benefits in a larger population of stroke survivors. To place this information in the context of current thinking about brain plasticity, this review outlines the basic theories of why spontaneous recovery occurs, and introduces important principles to explain the effects of post-stroke behavioral experience on neural plasticity.
Readers will be able to: (a) explain the three classic theories to explain spontaneous recovery after focal brain injury, (b) explain the neurophysiological effects of post-injury rehabilitative therapy on functional organization in motor cortex, (c) readers will be able to describe some of the variables that impact the effects of post-stroke behavioral experience on neuroplasticity, and (d) readers will be able to explain some of the current laboratory-based approaches to modifying brain circuits after stroke that might soon be translated to human application.
stroke; plasticity; recovery; rehabilitation
Background and Purpose
Our goal was to investigate whether certain metabolites, specific to neurons, glial cells, or the neuronal-glial neurotransmission system, in primary motor cortices (M1), are altered and correlated with clinical motor severity in chronic stroke.
Fourteen survivors of a single ischemic stroke located outside the M1 and 14 age-matched healthy control subjects were included. At >6 months after stroke, N-acetylaspartate, myo-inositol, and glutamate/glutamine were measured using proton magnetic resonance spectroscopic imaging (in-plane resolution=5×5 mm2) in radiologically normal-appearing gray matter of the hand representation area, identified by functional MRI, in each M1. Metabolite concentrations and analyses of metabolite correlations within M1 were determined. Relationships between metabolite concentrations and arm motor impairment were also evaluated.
The stroke survivors showed lower N-acetylaspartate and higher myo-inositol across ipsilesional and contral-esional M1 compared with control subjects. Significant correlations between N-acetylaspartate and glutamate/glutamine were found in either M1. Ipsilesional N-acetylaspartate and glutamate/glutamine were positively correlated with arm motor impairment and contralesional N-acetylaspartate with time after stroke.
Our preliminary data demonstrated significant alterations of neuronal-glial interactions in spared M1 with the ipsilesional alterations related to stroke severity and contralesional alterations to stroke duration. Thus, MR spectroscopy might be a sensitive method to quantify relevant metabolite changes after stroke and consequently increase our knowledge of the factors leading from these changes in spared motor cortex to motor impairment after stroke.
1H-MRS; motor impairment; plasticity; primary motor cortex; stroke; plasticity
This study describes the pattern of interhemispheric connections of the ventral premotor cortex (PMv) distal forelimb representation (DFL) in squirrel monkeys. Our objectives were to describe qualitatively and quantitatively the connections of PMv with contralateral cortical areas. Intracortical microstimulation techniques (ICMS) guided the injection of the neuronal tract tracers biotinylated dextran amine or Fast blue into PMv DFL. We classified the interhemispheric connections of PMv into three groups. Major connections were found in the contralateral PMv and supplementary motor area (SMA). Intermediate interhemispheric connections were found in the rostral portion of the primary motor cortex, the frontal area immediately rostral and ventral to PMv (FR), cingulate motor areas (CMAs), and dorsal premotor cortex (PMd). Minor connections were found inconsistently across cases in the anterior operculum (AO), posterior operculum/inferior parietal cortex (PO/IP), and posterior parietal cortex (PP), areas that consistently show connections with PMv in the ipsilateral hemisphere. Within-case comparisons revealed that the percentage of PMv connections with contralateral SMA and PMd are higher than the percentage of PMv connections with these areas in the ipsilateral hemisphere; percentages of PMv connections with contralateral M1 rostral, FR, AO, and the primary somatosensory cortex are lower than percentages of PMv connections with these areas in the ipsilateral hemisphere. These studies increase our knowledge of the pattern of interhemispheric connection of PMv. They help to provide an anatomical foundation for understanding PMv’s role in motor control of the hand and interhemispheric interactions that may underlie the coordination of bimanual movements.
connections; contralateral; interhemispheric; monkey; neuroanatomy; premotor cortex
The past decade of neuroscience research has provided considerable evidence that the adult brain can undergo substantial reorganization following injury. For example, following an ischemic lesion, such as occurs following a stroke, there is a cascade of molecular, genetic, physiological and anatomical events that allows the remaining structures in the brain to reorganize. Often, these events are associated with recovery, suggesting that they contribute to it. Indeed, the term plasticity in stroke research has had a positive connotation historically. But more recently, efforts have been made to differentiate beneficial from detrimental changes. These notions are timely now that neurorehabilitative research is developing novel treatments to modulate, increase, or inhibit plasticity in targeted brain regions. We will review basic principles of plasticity and some of the new and exciting approaches that are currently being investigated to shape plasticity following injury in the central nervous system.
Cortex; Stimulation; Plasticity; Recovery; Rehabilitation; Stroke
Vascular endothelial growth factor (VEGF) is thought to contribute to both neuroprotection and angiogenesis after stroke. While increased expression of VEGF has been demonstrated in animal models after experimental ischemia, these studies have focused almost exclusively on the infarct and peri-infarct regions. The present study investigated the association of VEGF to neurons in remote cortical areas at three days after an infarct in primary motor cortex (M1). Although these remote areas are outside of the direct influence of the ischemic injury, remote plasticity has been implicated in recovery of function. For this study, intracortical microstimulation techniques identified primary and premotor cortical areas in a non-human primate. A focal ischemic infarct was induced in the M1 hand representation, and neurons and VEGF protein were identified using immunohistochemical procedures. Stereological techniques quantitatively assessed neuronal-VEGF association in the infarct and peri-infarct regions, M1 hindlimb, M1 orofacial, and ventral premotor hand representations, as well as non-motor control regions. The results indicate that VEGF protein significantly increased association to neurons in specific remote cortical areas outside of the infarct and peri-infarct regions. The increased association of VEGF to neurons was restricted to cortical areas that are functionally and/or behaviorally related to the area of infarct. There was no significant increase in M1 orofacial region or in non-motor control regions. We hypothesize that enhancement of neuronal VEGF in these functionally related remote cortical areas may be involved in recovery of function after stroke, through either neuroprotection or the induction of remote angiogenesis.
VEGF (vascular endothelial growth factor); neuron; stroke; focal cerebral ischemia; stereology; neuroprotection
Background and Purpose
Residual motor deficits frequently linger after stroke. Search for newer effective strategies to promote functional recovery is ongoing. Brain stimulation, as a means of directing adaptive plasticity, is appealing. Animal studies and Phase I and II trials in humans have indicated safety, feasibility, and efficacy of combining rehabilitation and concurrent invasive cortical stimulation. However, a recent Phase III trial showed no advantage of the combination. We critically review results of various trials and discuss the factors that contributed to the distinctive result.
Summary of Review
Regarding cortical stimulation, it is important to determine the (1) location of peri-infarct representations by integrating multiple neuroanatomical and physiological techniques; (2) role of other mechanisms of stroke recovery; (3) viability of peri-infarct tissue and descending pathways; (4) lesion geometry to ensure no alteration/displacement of current density; and (5) applicability of lessons generated from noninvasive brain stimulation studies in humans. In terms of combining stimulation with rehabilitation, we should understand (1) the principle of homeostatic plasticity; (2) the effect of ongoing cortical activity and phases of learning; and (3) that subject-specific intervention may be necessary.
Future cortical stimulation trials should consider the factors that may have contributed to the peculiar results of the Phase III trial and address those in future study designs.
electrical stimulation of the brain; neuronal plasticity; recovery of function; stroke rehabilitation
Clinical and experimental data support a role for the intact cortex in recovery of function after stroke, particularly ipsilesional areas interconnected to the infarct. There is, however, little understanding of molecular events in the intact cortex, as most studies focus on the infarct and peri-infarct regions. This study investigated neuronal immunoreactivity for hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2) in remote cortical areas 3 days after a focal ischemic infarct, as both HIF-1α and VEGFR-2 have been implicated in peri-infarct neuroprotection. For this study, intracortical microstimulation techniques defined primary motor (M1) and premotor areas in squirrel monkeys (genus Saimiri). An infarct was induced in the M1 hand representation, and immunohistochemical techniques identified neurons, HIF-1α and VEGFR-2. Stereologic techniques quantified the total neuronal populations and the neurons immunoreactive for HIF-1α or VEGFR-2. The results indicate that HIF-1α upregulation is confined to the infarct and peri-infarct regions. Increases in VEGFR-2 immunoreactivity occurred; however, in two remote regions: the ventral premotor hand representation and the M1 hindlimb representation. Neurons in these representations were previously shown to undergo significant increases in VEGF protein immunoreactivity, and comparison of the two data sets showed a significant correlation between levels of VEGF and VEGFR-2 immunoreactivity. Thus, while remote areas undergo a molecular response to the infarct, we hypothesize that there is a delay in the initiation of the response, which ultimately may increase the ‘window of opportunity’ for neuroprotective interventions in the intact cortex.
VEGF (vascular endothelial growth factor); VEGF receptor-2 (VEGFR-2); HIF-1α (hypoxia inducible factor-1α); stroke; neuron; stereology
Therapeutic strategies to promote recovery from stroke are now beginning to utilize current knowledge of neural plasticity and the neuromodulatory role of physical rehabilitation. Current interests are also focused on adjuvant therapies that may enhance plasticity associated with recovery and rehabilitation. Amphetamine was one of the earliest pharmacological interventions and continues to show promising results as an adjuvant treatment for recovery of function in pre-clinical animal studies. This drug is a potent modulator of neurological function and cortical excitation, acting primarily through norepinephrine and dopamine mechanisms to enhance arousal and attention, and thus, to facilitate learning of motor skills. Although the results from the pre-clinical studies have been primarily positive, they have not translated well to clinical trials, which have yielded mixed results. This review addresses some of the conflicting evidence from pre-clinical studies conducted between 1982 and 2008 in order to better understand how to optimize the clinical application of amphetamine as an adjuvant therapy for stroke recovery. Among many of the factors that relate to differences in outcome, it is likely that both amphetamine dose and the timing of the intervention with respect to the time of injury affected the outcome.
Stroke; recovery; amphetamine; physical therapy; plasticity
Previous research has demonstrated that training rats in a skilled reaching condition will induce task-related changes in the caudal forelimb area of motor cortex. The purpose of the present study was to determine whether task-specific changes can be induced within the orofacial area of the motor cortex in rats. Specifically, we compared changes of the orofacial motor cortical representation in lick-trained rats to age-matched controls. For one month, six water-restricted Sprague-Dawley rats were trained to lick an isometric force-sensing disc at increasing forces for water reinforcement. The rats were trained daily for six minutes starting with forces of 1g, and increasing over the course of the month to 10, 15, 20, 25 and finally 30 g. One to three days following the last training session, the animals were subjected to a neurophysiological motor mapping procedure in which motor representations corresponding to the orofacial and adjacent areas were defined using intracortical microstimulation (ICMS) techniques. We found no statistical difference in the topographical representation of the control (mean = 2.03 mm2) vs. trained (1.87 mm2) rats. This result indicates that force training alone is insufficient to drive changes in the size of the cortical representation. We also recorded the minimum current threshold required to elicit a motor response at each site of microstimulation. We found that the lick-trained rats had a significantly lower average minimum threshold (29.1 ± 1.0 μA) for evoking movements related to the task compared to control rats (34.6 ± 1.1 μA). These results indicate that while tongue force training alone does not produce lasting changes in the size of the orofacial cortical motor representation, tongue force training decreases the current thresholds necessary for eliciting an ICMS-evoked motor response.
oromotor; plasticity; movement; licking; tongue; operant; cortical; training
A decision algorithm was required to evaluate the first half of a cooperative agreement for preclinical trials to optimize medical device parameters to enhance stroke recovery. Continued funding was contingent upon the midpoint evaluation, called the milestone decision. We developed an algorithm, which summarized our rodent and primate model results. Primary outcomes weighed more heavily than secondary outcomes, and the primate model more heavily than rodent models. By controlling the type I error for this milestone decision, the probability of correctly discontinuing the study if treatment was not beneficial was high (>0.84). Similar algorithms may be adapted for other milestone-driven projects.
cooperative agreement; milestones; translational research; type I error