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PubMed2005

Modification of statocyst input to local interneurons by behavioral condition in the crayfish brain.

Posture control by statocysts is affected by leg condition in decapod crustaceans. We investigated how, in the crayfish brain, the synaptic response of local interneurons to statocyst stimulation was affected by leg movements on and off a substratum. The magnetic field stimulation method permitted sustained stimulation of statocyst receptors by mimicking body rolling. The statocyst-driven local interneurons were classified into four morphological groups (Type-I-IV). All interneurons except Type-IV projected their dendritic branches to the parolfactory lobe of the deutocerebrum where statocyst afferents project directly. Type-I interneurons having somata in the ventral-paired lateral cluster responded invariably to statocyst stimulation regardless of the leg condition, whereas others having somata in the ventral-unpaired posterior cluster showed response enhancement or suppression, depending on the cell, during leg movements on a substratum, but no response change during free leg movements off the substratum. The synaptic responses of Type-II and IV interneurons were also affected differently by leg movements depending on the substratum condition, whereas those of Type-III remained unaffected. These findings suggest that the statocyst pathway in the crayfish brain is organized in parallel with local circuits that are affected by leg condition and those not affected.

Action Potentials↗

PubMed2006

Predicting falls in individuals with Parkinson disease: a reconsideration of clinical balance measures.

BACKGROUND AND PURPOSE: Postural control problems, falls, and fall-related injuries are a common source of morbidity in elderly individuals, especially those with Parkinson disease (PD). Clinical balance tests such as the Berg balance scale and the functional reach have been reported to be useful in assessing fall risk in elderly individuals. However, the utility of commonly used clinical balance tests as accurate screens for fall risk has not been sufficiently examined in persons with PD. The purposes of this study were to identify which commonly used clinical balance tests of persons with PD were predictive of falls, to re-examine the cutoff scores for these tests with the goal of maximizing sensitivity as well as minimizing the negative likelihood ratio, and to determine which of the clinical balance tests had the most value in predicting falls. PARTICIPANTS: Forty-five persons with a diagnosis of idiopathic PD, aged 39-90 years (mean [sd] =69.94 [11.28]; mean [sd] Hoehn and Yahr level = 2.60 [.66]) participated. METHODS: Upon initial contact with participants, demographics and fall history were gathered and baseline physical examinations were performed. Each individual underwent balance testing with the functional reach test, the Berg balance scale, the dynamic gait index, timed up and go, and the cognitive timed up and go. Fallers and nonfallers were divided based on fall history and groups were compared on balance test performance. Sensitivity, specificity, likelihood ratios, and receiver operator characteristic curves were calculated for all balance tests. RESULTS: Twenty-five (55%) participants had a history of falls. Using cut-off scores reported in previous studies, the sensitivity of all tests was low (less than 0.60) and the specificity was high (greater than 0.85). Reconsideration of the cut-off scores resulted in increased sensitivity for all tests (greater than 0.75) and low negative likelihood ratios (less then .30). DISCUSSION AND CONCLUSION: Given the large financial, psychological, and physical complications that are associated with a fall and relatively little harmful effects of fall prevention interventions, we propose consideration of cut-off scores that maximize sensitivity for individuals with PD. Regardless of the performance on any individual clinical balance test, the multifactorial nature of postural instability in PD may necessitate a battery of tests to provide the most accurate identification of fall risk.

Accidental Falls↗

PubMed2000

Static stabilometry and repeated testing in a normal population.

BACKGROUND: The purpose of the present study was to see if there is a learning effect of repeated static stabilometric testing, using a protocol suitable for testing postural control in narrow spaces, like hypo- and hyperbaric chambers. HYPOTHESIS: Static stabilometry testing under normobaric conditions is objective and reproducible. With repeated testing, a learning effect may be observed. METHODS: Four groups of healthy individuals were tested ten times under the same four acoustically and visually standardized and normobaric normoxic test conditions on a static balance platform. First, the subjects were asked to stand on a bare platform with the eyes open, thereafter with the eyes closed. This was repeated with a foam rubber mat placed on top of the balance platform. The time interval between the first and the last test sequence was 11 (10-13) days for the test subjects in group I (n = 22), 17 d for group II (n = 13), 31(28-36) days for group III (n = 15) and 115 (49-193) days for group IV (n = 10). RESULTS: Static stabilometry tests in a normal population are objective and reproducible. With repeated tests, a learning effect was observed. The learning effect was largest when standing on a foam rubber mat with eyes closed and when the time intervals between the tests were shortest. There was no difference in sway pattern or learning ability between tall and short test subjects, between subjects with heavy and light body weight or between the sexes.

Adult↗

PubMed2003

Effects of leg movements on the synaptic activity of descending statocyst interneurons in crayfish, Procambarus clarkii.

Crustacean postural control is modulated by behavioral condition. In this study, we investigated how the responses of descending statocyst interneurons were affected during leg movements. Intracellular recording was made from an animal whose statoliths had been replaced with ferrite grains so that statocyst receptors could be activated by magnetic field stimulation. We identified 14 morphological types of statocyst-driven descending interneurons. Statocyst-driven descending interneurons always showed an excitatory response to statocyst stimulation on either ipsilateral or contralateral side to the axon. The response of each statocyst-driven descending interneuron to statocyst stimulation was differently modulated by leg movements in different conditions. During active leg movements, six statocyst-driven descending interneurons were activated regardless of whether a substrate was provided or not. In other two statocyst-driven descending interneurons, the excitatory input during leg movements was stronger when a substrate was provided than when it was not. One statocyst-driven descending interneuron received an excitatory input only during leg movements on a substrate, whereas another statocyst-driven descending interneuron did not receive any input during leg movements both on a substrate and in the air. These results suggest that the descending statocyst pathways are organized in parallel, each cell affected differently by behavioral conditions.

Action Potentials↗

PubMed2004

Comparison of three methods to estimate the center of mass during balance assessment.

Evaluation of postural control is generally based on the interpretation of the center of pressure (COP) and the center of mass (COM) time series. The purpose of this study is to compare three methods to estimate the COM which are based on different biomechanical considerations. These methods are: (1) the kinematic method; (2) the zero-point-to-zero-point double integration technique (GLP) and (3) the COP low-pass filter method (LPF). The COP and COM time series have been determined using an experimental setup with a force plate and a 3D kinematic system on six healthy young adult subjects during four different 30 s standing tasks: (a) quiet standing; (b) one leg standing; (c) voluntary oscillation about the ankles and (d) voluntary oscillation about the ankles and hips. To test the difference between the COM trajectories, the root mean square (RMS) differences between each method (three comparisons) were calculated. The RMS differences between kinematic-LPF and GLP-LPF are significantly larger than kinematic-GLP. Our results show that the GLP method is comparable to the kinematic method. Both agree with the unified theory of balance during upright stance. The GLP method is attractive in the clinical perspective because it requires only a force plate to determine the COP-COM variable, which has been demonstrated to have a high reliability.

Adult↗

PubMed2002

Balance in a rotating artificial gravity environment.

When subjects stand at the center of a fully enclosed room that is rotating at constant velocity, their natural postural sway generates Coriolis forces that destabilize their center of mass and head. We quantitatively assessed how exposure to constant velocity rotation at 10 rpm affected postural control. Twelve subjects stood in a heel-to-toe stance in the rotating room. Each test session involved three phases: (1) pre-rotation, (2) per-rotation, and (3) post-rotation. In each phase, subjects were tested in both eyes open and eyes closed conditions. Four measures were used to characterize center of mass movement and head movement: mean sway amplitude, total power, mean power frequency, and frequency of maximum power. Each measure was computed for anterior-posterior and medial-lateral sway. Both anterior-posterior and medial-lateral head and center of mass sway during rotation had significantly greater mean sway amplitude and total power compared with pre- and post-rotation values. Mean power frequency and frequency of maximum power were little affected. Eyes open conditions were significantly more stable in all test phases than eyes-closed, but vision did not completely suppress the effects of rotation. The greatest effect of rotation was in the eyes-closed condition with mean sway amplitude and total power increasing more than twofold. Inverted pendulum sway was maintained in all phases of both test conditions. No aftereffects of rotation were present after the four 25-s exposures each subject received. We expect that with longer exposure periods and with active generation of body sway subjects would both adapt to rotation and exhibit post-rotary aftereffects.

Adult↗

PubMedDate not supplied

Motor dysfunction in a mouse model for Down syndrome.

Motor deficits are among the most frequently occurring features of Down syndrome (DS). Individuals with DS exhibit disturbances in the dynamics of movement production and postural control that are thought to have a significant impact in delaying their acquisition of motor skills. The origin of these deficits has been hypothesized to be cerebellar. The Ts65Dn mouse is the most robust and genetically sound animal model for DS currently available. Ts65Dn mice show many DS-like features, including significant learning deficits in different behavioral tasks and neurodegeneration of cholinergic neurons. In the present study, we investigate the motor function of these animals. We have analyzed hind paw print patterns during walking, running speeds, rotarod performance, grip force production, swim paths, and swimming speeds. Our results indicate that Ts65Dn mice present mild to severe dysfunction according to all of the above assessments. The most evident impairments presented by these mice were related to equilibrium and motor coordination, which agrees with reported clinical observations made on individuals with DS. Because none of these findings were readily apparent by simple inspection of these animals, these findings reiterate the need for a careful evaluation of any mutant mouse strain for which there is reason to suspect motor deficits. The identification of motor dysfunction in Ts65Dn mice may have important consequences for the interpretation of some previous assessments of learning and memory of these animals that assumed intact motor function, and further strengthens the use of this aneuploid mouse strain as a model for DS.

Animals↗

PubMed2005

Intrinsic membrane properties of vertebrate vestibular neurons: function, development and plasticity.

Central vestibular neurons play an important role in the processing of body motion-related multisensory signals and their transformation into motor commands for gaze and posture control. Over recent years, medial vestibular nucleus (MVN) neurons and to a lesser extent other vestibular neurons have been extensively studied in vivo and in vitro, in a range of species. These studies have begun to reveal how their intrinsic electrophysiological properties may relate to their response patterns, discharge dynamics and computational capabilities. In vitro studies indicate that MVN neurons are of two major subtypes (A and B), which differ in their spike shape and after-hyperpolarizations. This reflects differences in particular K(+) conductances present in the two subtypes, which also affect their response dynamics with type A cells having relatively low-frequency dynamics (resembling "tonic" MVN cells in vivo) and type B cells having relatively high-frequency dynamics (resembling "kinetic" cells in vivo). The presence of more than one functional subtype of vestibular neuron seems to be a ubiquitous feature since vestibular neurons in the chick and frog also subdivide into populations with different, analogous electrophysiological properties. The ratio of type A to type B neurons appears to be plastic, and may be determined by the signal processing requirements of the vestibular system, which are species-variant. The membrane properties and discharge pattern of type A and type B MVN neurons develop largely post-natally, through the expression of the underlying ion channel conductances. The membrane properties of MVN neurons show rapid and long-lasting plastic changes after deafferentation (unilateral labyrinthectomy), which may serve to maintain their level of activity and excitability after the loss of afferent inputs.

Action Potentials↗

PubMed2004

Contraversive pushing in non-stroke patients.

BACKGROUND: Pusher syndrome is a disorder of postural control observed in patients with right or left brain damage associated with hemiparesis. Those patients show a peculiar behavior of actively pushing away from the nonhemiparetic side and resisting against passive correction, with a tendency to fall toward the paralyzed side. Thus far this phenomenon has been exclusively associated with stroke patients. OBJECTIVE: We investigate the occurrence, imaging features and clinical evolution of pusher behavior in patients with acute encephalic lesions at a tertiary emergency hospital. METHODS: Pusher patients were identified from 530 inpatients during a 1 year period. Patients were evaluated using a standardized Scale for Contraversive Pushing (SCP), neurological examination, assessment of neuropsychological symptoms, activities of daily living function and neuroimaging studies. RESULTS: We found eight patients (1.5%) with severe contraversive pushing, three female and five male. Age at symptoms onset ranged from 48 to 80 years (mean 65.4). All patients had scores equal or above 1.5 in each tested parameter of the SCP. Six patients (75 %) had right-hemisphere brain damage. A stroke etiology was found in four patients. The other four patients had non-stroke etiology (three traumatic, one metastatic tumor). Stroke patients showed complete recovery of pusher behavior at a mean duration of 15.3 weeks. In patients with brain trauma, pushing behavior was completely resolved in a mean time of 5 weeks. CONCLUSIONS: The results demonstrate that contraversive pushing may also occur in patients with non-stroke neurological lesions and suggest that resolution of symptoms may vary according to the underlying etiology.

Aged↗

PubMed1998

Parasolitary nucleus: a source of GABAergic vestibular information to the inferior olive of rat and rabbit.

At least two subnuclei of the inferior olive, the beta-nucleus, and the dorsomedial cell column (dmcc), contain vestibularly responsive neurons that receive a dense descending projection that uses gamma-aminobutyric acid (GABA) as the transmitter. In contrast to the GABAergic innervation of other olivary subnuclei, the terminal boutons that terminate on neurons in the beta-nucleus and the dorsomedial cell column remain intact after cerebellectomy, ruling out both the cerebellum and the cerebellar nuclei as afferent sources. By using both immunohistochemical as well as orthograde and retrograde tracer methods, we have identified the source of the GABAergic pathway to the beta-nucleus and dmcc in both rat and rabbit. Under physiologic recording of single olivary neurons to guide electrode placement, we injected the bidirectional tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the beta-nucleus and dmcc of the inferior olive. These injections retrogradely labeled neurons in the parasolitary nucleus (Psol) near the vestibular complex. Psol neurons were identified as GABAergic with an antibody to glutamic acid decarboxylase (GAD). In the rat, Psol neurons are small (5-7 microm in diameter) and number approximately 1,800. In the rabbit, they are slightly larger (6-9 microm in diameter) and number approximately 2,200. WGA-HRP injections in conjunction with GAD immunohistochemistry double labeled a high percentage of neurons in both the rat and rabbit Psol. Injection of the orthograde tracer Phaseolus vulgaris-leucoagglutinin into the area of the Psol revealed a projection from this region to both the beta-nucleus and dmcc. Subtotal electrolytic lesions of this division of the Psol caused a substantial reduction in GAD-positive synaptic terminals in both the ipsilateral beta-nucleus and dmcc. The location of these GABAergic neurons, bordering both the nucleus solitarius and caudal vestibular complex, emphasizes the importance of the Psol in the processing of both vestibular and autonomic information pertinent to postural control.

Animals↗

PubMed1998

Polyneural innervation in the psoas muscle of the developing rat.

Polyneural innervation was studied in the psoas muscle in developing rats from P4 till P25 and at adult age, with the combined silver-acetylcholinesterase technique. Nerve endings were counted, and end-plates were measured. These data were compared with such data in the human. The end of polyneural innervation in the rat (around P20) and in the human (around 12 weeks postterm age) in both cases coincides with a transformation in motor behavior and postural control. The rat's psoas muscle at early stages is less heavily innervated than this muscle in the human. Up to three axons per motor end-plate were counted at P4, but in the human up to five axons at 25 weeks of post menstrual age. This difference might be related to the lower percentage of type I muscle fibers in the rat.

Animals↗

PubMed1996

The organization of leg movements in preterm and full-term infants after term age.

In a sample of 13 full-term and 10 preterm infants, the development of kicking movements was studied at 6, 12, and 18 weeks (corrected) age. In healthy full-term infants some characteristics are strikingly stable, such as the duration of the flexion and extension phase and the within-joint organization. These parameters did not differ in preterm compared to full-term infants. For other features, however, developmental changes and differences were observed. Full-term infants tended to decrease their kick frequencies slightly with age. In preterm infants much higher initial kick rates were found, followed by a steep decrease, which resulted in kick frequencies comparable to the full-term levels after the (corrected) age of 12 weeks. There is a tight coupling between the movements in the different joints of the leg in full-term newborns. Preterm infants, in contrast, initially show much lower cross-correlations between hip and ankle and between knee and ankle. This is particularly the case for those preterm infants who were born before 32 weeks gestation. Again, the differences resolved after the age of 12 weeks, which might be related to a transformation in neural functions reported previously around this age. The initial differences in the characteristics of kicking appeared to be more readily explainable by differences in neurological condition than by contrasts in leg volume or postural control.

Birth Weight↗

PubMed2004

The postnatal developmental expression pattern of urocortin in the rat olivocerebellar system.

Urocortin belongs to the family of corticotropin-releasing factor (CRF)-like peptides, which play an important role in sensorimotor coordination. CRF induces locomotor activity, and urocortin has an inhibitory effect. Here, we document the regional and subcellular localization of urocortin in the developing rat cerebellum to compare it with CRF. During the first postnatal week, urocortin immunoreactivity (UCN-ir), within the white matter and cerebellar cortex, was strongest in vermal lobules I, II, IX, and X, closely followed by lobules IV, V, and VIII; lobules VI and VII showed the weakest labeling. Cortical immunoreactivity was in the form of puncta that encircled Purkinje cell somata. By postnatal day (PD) 12, UCN-ir had increased appreciably in all lobules. In Purkinje cells, labeling was spread throughout their somata and proximal dendrites. By PD 15, labeling in lobules I-IV appeared to wane, yet still prevailed in the central and posterior lobules. This anterior-to-posterior gradient persisted through to adulthood. The study shows that urocortin and CRF have similar regional distribution profiles during development, suggesting synergistic roles within the vestibulocerebellum. The onset of the adult distributional pattern of urocortin at the stage when rats are capable of fluent walking patterns further strengthens the correlation between CRF-like peptides and postural control. An important difference between urocortin and CRF is the localization of urocortin, and not CRF, within Purkinje cells, implying that urocortin probably has an additional role in modulating the signals emanating from the cerebellar cortex to the deep cerebellar nuclei.

Animals↗

PubMed2005

Medial vestibular connections with the hypocretin (orexin) system.

The mammalian medial vestibular nucleus (MVe) receives input from all vestibular endorgans and provides extensive projections to the central nervous system. Recent studies have demonstrated projections from the MVe to the circadian rhythm system. In addition, there are known projections from the MVe to regions considered to be involved in sleep and arousal. In this study, afferent and efferent subcortical connectivity of the medial vestibular nucleus of the golden hamster (Mesocricetus auratus) was evaluated using cholera toxin subunit-B (retrograde), Phaseolus vulgaris leucoagglutinin (anterograde), and pseudorabies virus (transneuronal retrograde) tract-tracing techniques. The results demonstrate MVe connections with regions mediating visuomotor and postural control, as previously observed in other mammals. The data also identify extensive projections from the MVe to regions mediating arousal and sleep-related functions, most of which receive immunohistochemically identified projections from the lateral hypothalamic hypocretin (orexin) neurons. These include the locus coeruleus, dorsal and pedunculopontine tegmental nuclei, dorsal raphe, and lateral preoptic area. The MVe itself receives a projection from hypocretin cells. CTB tracing demonstrated reciprocal connections between the MVe and most brain areas receiving MVe efferents. Virus tracing confirmed and extended the MVe afferent connections identified with CTB and additionally demonstrated transneuronal connectivity with the suprachiasmatic nucleus and the medial habenular nucleus. These anatomical data indicate that the vestibular system has access to a broad array of neural functions not typically associated with visuomotor, balance, or equilibrium, and that the MVe is likely to receive information from many of the same regions to which it projects.

Animals↗

PubMed1988

Comparative topography of projections from the mesodiencephalic junction to the inferior olive, vestibular nuclei, and upper cervical cord in the cat.

Distributions of neurons located in the central rostral mesencephalon and caudal diencephalon that project to the upper cervical spinal cord, vestibular nuclei, or inferior olive were studied in the cat by using retrograde axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Afferent sources to all of these targets were observed in the interstitial nucleus of Cajal (INC), the region surrounding the fasciculus retroflexus (PF), and the nucleus of the fields of Forel (NFF). Three-dimensional reconstruction revealed differences in densities of cells projecting from these common areas. Spinal projecting cells were present in slightly greater numbers in the caudal two-thirds of the INC, whereas those projecting to the vestibular complex were more numerous in the rostral two-thirds of this nucleus. A relatively smaller number of olivary projecting cells were dispersed throughout the INC. Olivary afferent sources outnumber those with spinally directed or vestibularly directed axons in the PF region. In the fields of Forel, cells projecting to the vestibular nuclei or inferior olive were concentrated medially, whereas cells projecting to the spinal cord appeared both medially and laterally. Each type of afferent source was also seen in the nucleus of the posterior commissure and the posterior ventral lateral hypothalamic area. Unique sources of afferents to the inferior olive were observed in the parvicellular red nucleus (ipsilateral to the injections) and the anterior and posterior pretectal nuclei. A large number of labeled neurons was seen in the nucleus of Darkschewitsch after injections of tracer into the inferior olive, but this projection did not appear to be unique, as small numbers of labeled cells were also seen after injections into the cervical spinal cord. The Edinger-Westphal nucleus and the adjacent somatic oculomotor nucleus contained cells which projected separately to the spinal cord or the vestibular complex, and the superior colliculus contained cells which projected separately to the contralateral spinal cord or the contralateral inferior olive. In this study, it was also noted that neurons in the medial terminal nucleus of the accessory optic tract projected to the ipsilateral inferior olive or to the contralateral vestibular complex. These differences in locations and densities of cells projecting to the cervical spinal cord, vestibular complex, and inferior olive may underlie functional specializations in these areas in relation to vertical eye and head movement control and to neural systems controlling postural adjustments accompanying limb movements.

Afferent Pathways↗

PubMedDate not supplied

Falls in the rehabilitation setting: incidence and characteristics.

A prospective six-month study was conducted to determine a high-risk index for medical rehabilitation patients who fall. Variables studied for all patients included demographics, medical conditions, associated symptoms, orthostatic blood pressure measurements, physical function, posture control, proprioception, use of physical restraints, and medications, A detailed examination of the fall events was also conducted. Of the 143 patients studied, 46 (32%) fell at least once, making a total of 84 falls. Impaired ability to follow directions, impaired judgment, impaired proprioception, presence of physical restraints, use of major tranquilizers, use of sedatives, and presence of psychiatric diagnosis were all individually associated with patients who fell. Males fell more than females. Logistic regression identified altered proprioception as the only major predictor of falling. Of those who fell, only 26% called for assistance prior to the fall. Sixty-eight percent of the falls were from wheelchairs. Importantly, no patients had serious injury or morbidity from the falls.

Accidental Falls↗

PubMed1997

Severe tardive dystonia: treatment with continuous intrathecal baclofen administration.

Treatment of tardive dystonia with oral baclofen produces ambivalent and overall disappointing results. However, because only a small proportion of the baclofen penetrates into the central nervous system when administered orally, we tested whether it is possible to increase the efficacy of treatment by continuous intrathecal infusion of baclofen (CITB) in a patient with severe tardive axial dystonia unresponsive to conventional therapy. A dose of 100 micrograms/day improved muscle tone, head control, posture, and walking distance; electromyography showed a marked decrease of dystonic muscle activity with fully preserved voluntary muscle activity, and the patient reported substantial reduction of pain. Apart from some minor discomfort at the site of operation, no side effects were noted. Further studies should be encouraged to evaluate the usefulness of CITB for other patients with severe and otherwise untreatable tardive dystonia.

Antipsychotic Agents↗

PubMed2001

Contractile properties of human motor units in health, aging, and disease.

The primary function of skeletal muscle is to produce force for postural control and movement. Although the contractile properties of the whole muscle are useful functional indicators, they do not accurately reflect the heterogeneity of the constituent motor units (MUs) and their changes in health and disease. However, data on the contractile properties of human MUs, in comparison to other animal species, are relatively sparse. This, in part, is due to greater methodological challenges of in vivo studies of MUs in the human. The purpose of this review is to critically appraise the methods used in humans; to describe the normative data from different muscle groups; to discuss differences between data from healthy humans and other animal species; and, last, to characterize changes of the MU contractile properties in aging, disease, and in response to intervention. Because the spike-triggered averaging technique can only be used to study the twitch properties, other methods were subsequently developed to measure a wider range of contractile properties. Although there is general agreement between human data and those from other animal species, major differences do exist. Potential reasons for these discrepancies include true biological differences, but differences in the techniques used may also be responsible. Although limited, measurement of MU contractile properties in humans has provided insight into the changes associated with aging and motoneuronal diseases and provides a means of gauging their adaptive capacity for training and immobilization.

Aging↗