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PubMed2001

Spinal and supraspinal factors in human muscle fatigue.

Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for "central" fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal changes in cortical excitability and inhibitability based on electromyographic (EMG) recordings, and a decline in supraspinal "drive" based on force recordings. Some of the changes in motor cortical behavior can be dissociated from the development of this "supraspinal" fatigue. Central changes also occur at a spinal level due to the altered input from muscle spindle, tendon organ, and group III and IV muscle afferents innervating the fatiguing muscle. Some intrinsic adaptive properties of the motoneurons help to minimize fatigue. A number of other central changes occur during fatigue and affect, for example, proprioception, tremor, and postural control. Human muscle fatigue does not simply reside in the muscle.

Animals↗

PubMed2001

Normal and abnormal development of motor behavior: lessons from experiments in rats.

In this essay a few relevant aspects of the neural and behavioral development of the brain in the human and in the rat are reviewed and related to the consequences of lesions in the central and peripheral nervous system at early and later age. Movements initially are generated by local circuits in the spinal cord and without the involvement of descending projections. After birth, both in humans and in rats it seems that the development of postural control is the limiting factor for several motor behaviors to mature. Strong indications exist that the cerebellum is significantly involved in this control. Lesions in the CNS at early stages interfere with fundamental processes of neural development, such as the establishment of fiber connections and cell death patterns. Consequently, the functional effects are strongly dependent on the stage of development. The young and undisturbed CNS, on the other hand, has a much greater capacity than the adult nervous system for compensating abnormal reinnervation in the peripheral nervous system. Animal experiments indicated that the cerebellar cortex might play an important part in this compensation. This possibility should be investigated further as it might offer important perspectives for treatment in the human.

Animals↗

PubMed2005

A critical review of constraint-induced movement therapy and forced use in children with hemiplegia.

Hemiplegia is a physical impairment that can occur in childhood following head trauma, cerebral vascular accident or transient ischemic attack (stroke), brain tumor, or congenital or perinatal injury. One of the most disabling symptoms of hemiplegia is unilaterally impaired hand and arm function. Sensory and motor impairments in children with hemiplegia compromise movement efficiency. Such children often tend not to use the affected extremity, which may further exacerbate the impairments, resulting in a developmentally learned non-use of the involved upper extremity, termed 'developmental disuse'. Recent studies suggest that children with hemiplegia benefit from intensive practice. Forced use and Constraint-Induced Movement Therapy (CI therapy) are recent therapeutic interventions involving the restraint of the non-involved upper extremity and intensive practice with the involved upper extremity. These approaches were designed for adults with hemiplegia, and increasing evidence suggests that they are efficacious in this population. Recently, forced use and constraint-induced therapy have been applied to children with hemiplegia. In this review, we provide a brief description of forced use and CI therapy and their historical basis, provide a summary of studies of these interventions in children, and discuss a number of important theoretical considerations, as well as implications for postural control. We will show that whereas the studies to date suggest that both forced use and CI therapy appear to be promising for improving hand function in children with hemiplegia, the data are limited. Substantially more work must be performed before this approach can be advocated for general clinical use.

Age Factors↗

PubMedDate not supplied

Aging and attenuated processing robustness. Evidence from cognitive and sensorimotor functioning.

BACKGROUND: Within-person, across-time variations in processes and performance are intrinsic to all aspects of human functioning. OBJECTIVE: This article starts with a brief taxonomy of intraindividual dynamics. There are adaptive as well as non-adaptive types of intraindividual variations that unfold with different degrees of reversibility on different time scales and involve either single, or systems of, functions. METHODS: Empirical findings regarding aging and a specific type of intraindividual variation, namely attenuated processing robustness, are then presented with respect to cognitive and sensorimotor functioning. RESULTS: In both domains of functioning, old adults exhibit less robust functioning with a greater amount of week-to-week, day-to-day, or trial-by-trial fluctuations in their cognitive, walking, and postural control performances. CONCLUSION: Currently, the causes for the attenuation of processing robustness in cognitive and sensorimotor functioning are not well understood. Neurocomputational models are useful tools for exploring the tripartite relationships between the aging of neural information-processing fidelity, and cognitive, and sensorimotor processes.

Aging↗

PubMed1992

Skin flow the venoarteriolar response and capillary filtration in diabetics. A 3-year follow-up.

Resting skin blood flow (RF) and the venoarteriolar response (VAR = the vasoconstrictor response on standing) have been studied in 100 patients with diabetic neuropathy, in 100 diabetics without neuropathy, and in 100 normal subjects by laser Doppler flowmetry. Capillary filtration was also studied with strain gauge plethysmography. The authors followed up these patients by evaluating their microcirculation again after three years. At the beginning of the study in patients with neuropathy, RF and capillary filtration were increased. The VAR and the microangiopathy index (MI = VAR/RF) were reduced in all diabetics, to a greater extent to those with neuropathy. After three years the authors observed an increase in capillary filtration associated with a further impairment in VAR and MI, suggesting progression of microangiopathy in both groups of diabetics. These results suggest that the postural control of blood flow in the skin of the foot is impaired in diabetic microangiopathy, particularly in neuropathics. Increased skin blood flow and capillary filtration and the impaired venoarteriolar response cause edema and may contribute to the thickening of capillary basement membranes and the progressive evolution of diabetic microangiopathy.

Adult↗

PubMed1996

Physical therapy interventions for patients with movement disorders due to cerebral palsy.

The purpose of this paper is to present evidence of the efficacy of physical therapy interventions for patients with cerebral palsy and identify goals for these patients. Studies suggest that neurodevelopmental treatment and Vojta techniques improve postural control. Little evidence supports the efficacy of early intervention, but researchers have not yet studied effects on the family. Strengthening, electrical stimulation, the use of orthoses, and seating show positive effects in studies of small numbers of subjects. For severely involved children, ease of care and comfort are important goals, as well as prevention of deformity, which is important for all children. To the extent possible, therapy should prepare a child for independent adult life. In early intervention through school age, therapy focuses on promoting communication, self-care, and mobility. Independence is a key issue for adolescents transitioning into adulthood. The rehabilitation and health needs of adults with cerebral palsy need to be addressed. Research needs to determine the effects of physical therapy not only on impairment but also on function and disability.

Adolescent↗

PubMed2005

Changes in infant segment inertias during the first three months of independent walking.

BACKGROUND: During infancy, rapid changes in physical growth affect the size and shape of the body segments. To understand the effects of growth on movement, it is first necessary to quantify rates of development during the acquisition of important motor milestones. The goal of this longitudinal study was to quantify the physical growth of infant body segments during the initial stages of independent walking. METHODS: Ten infants (N = 10) aged between 28 and 55 weeks at the beginning of the study were tested biweekly (every two weeks) for three months. A 13-segment mathematical model of the human body was used to estimate the inertial parameters of the infant body segments at each session. An analysis of variance was used to test for significant differences in segment masses between biweekly measures. Polynomial contrasts were used to test for linear trends in the growth data. RESULTS: Significant differences between biweekly measures of segment mass were found only for the head/neck (F(5,45) = 3.42, p < 0.05), upper trunk (F(5,45) = 4.04, p < 0.01), and lower trunk (F(5,45) = 3.49, p < 0.01). The lower trunk demonstrated a linear increase in mass (F(1,9) = 4.56, p < 0.05). However, the upper trunk demonstrated a quadratic trend in growth (F(1,9) = 9.13, p < 0.01), while the head/neck segment showed a cubic trend in growth (F(1,9) = 3.80, p < 0.05). Significant differences in axial segment masses were also found between subjects (F(9,45) = 5.92, p < 0.001). CONCLUSION: Given that postural control proceeds in a cephalocaudal manner, the lower trunk segment would be brought under control last, in terms of the axial segments. Increases in the mass of this segment could constrain the system, thereby acting as a control parameter for the onset and development of motor patterns.

Journal Article↗

PubMed2006

Second-order projection from the posterior lateral line in the early zebrafish brain.

BACKGROUND: Mechanosensory information gathered by hair cells of the fish lateral-line system is collected by sensory neurons and sent to the ipsilateral hindbrain. The information is then conveyed to other brain structures through a second-order projection. In the adult, part of the second-order projection extends to the contralateral hindbrain, while another part connects to a midbrain structure, the torus semicircularis. RESULTS: In this paper we examine the second-order projection from the posterior lateral-line system in late embryonic/early larval zebrafish. At four days after fertilization the synaptic field of the sensory neurons can be accurately targeted, allowing a very reproducible labeling of second-order neurons. We show that second-order projections are highly stereotyped, that they vary according to rhombomeric identity, and that they are almost completely lateralized. We also show that the projections extend not only to the contralateral hindbrain and torus semicircularis but to many other brain centers as well, including gaze- and posture-controlling nuclei in the midbrain, and presumptive thalamic nuclei. CONCLUSION: We propose that the extensive connectivity observed in early brain development reveals a basic scaffold common to most vertebrates, from which different subsets are later reinforced in various vertebrate groups. The large repertoire of projection targets provides a promising system to study the genetic encoding of this differential projection capacity.

Afferent Pathways↗

PubMed2006

Evaluation of physical therapy in parkinsonian patients with freezing of gait: a pilot study.

OBJECTIVE: Freezing of gait is a frequently disabling symptom in Parkinson's disease, poorly responding to dopaminergic treatment. We investigated the short-term effectiveness of a rehabilitation protocol in parkinsonian patients with freezing of gait. DESIGN: Prospective, uncontrolled pilot study with open label design. SETTING: Outpatient service for rehabilitation of neurological disorders. SUBJECTS: Twelve patients (8 male, 4 female; aged 59-78 years; Hoehn-Yahr stage: 2-3; mean disease duration: 14.2 +/- SD 4.1 years). INTERVENTIONS: Patients attended three (45 min) sessions every week, over a six-week period, of physical therapy focused to improve balance, postural control and walking, and to learn new strategies for overcoming freezing of gait. MAIN OUTCOME MEASURES: Patients were evaluated before (T0), at the end (T1), and one month after (T2) rehabilitation by means of clinical rating scales (Unified Parkinson Disease Rating Scale--Motor Section; Freezing of Gait Questionnaire; Parkinson Disease Quality of Life Score) and gait parameters (number of strides, stride length and velocity) during a standardized walking test. RESULTS: The scores of Freezing of Gait Questionnaire and of Parkinson Disease Quality of Life Questionnaire (but not of the Unified Parkinson Disease Rating Scale--Motor Section) were significantly improved after treatment (T1). Gait parameters were significantly improved at T1 and T2. CONCLUSIONS: We showed the potential short-term efficacy of a rehabilitative approach to freezing of gait in Parkinson's disease. The positive outcome was documented by clinical rating scales and objective gait evaluation. The rapid reversibility of the clinical benefit suggests that further studies are needed to better define the optimal frequency and duration of treatment.

Aged↗

PubMed2004

Trajectories of alcohol use and electrophysiological and morphological indices of brain development: distinguishing causes from consequences.

Alcoholism is a major public health problem. Patterns of drinking during adolescence can influence the likelihood of this outcome. Both environmental variation and familial/genetic susceptibility play important roles in this process. While there is some evidence to suggest that metabolic factors play a role in whether some individuals are protected from developing alcohol problems, there is substantial reason to look for cognitive factors that are associated with increased susceptibility. Developmental trajectories for information processing that can be reflected in P300 amplitude changes over time, as well as trajectories describing acquisition of postural control when compared in offspring from families with multiple cases of alcoholism or those with none or few, suggest that brain development provides a clue to why some individuals are more susceptible to becoming alcoholic. Finally, differences seen in amygdala volume between high- and low-risk adolescents suggest that functional differences seen in electrophysiological responding or neuropsychological test performance may have anatomical correlates.

Adolescent↗

PubMed2006

Discourse analytic study of counseling sessions in stroke physiotherapy.

Studies on the interaction between physiotherapists and patients during treatment sessions have found low levels of communicative participation by patients and lack of direct influence by patients on the content of their treatment. This article reports the results of 7 counseling sessions in which physiotherapists and patients with stroke and their caregivers discussed the patients' postural control and balance, which had been tested and videotaped at different stages of the rehabilitation process. The physiotherapists' discourses relating to the videotaped test performances were either brief comments on the patient's performance or critical appraisals with references to difficulties encountered during performance. Performances of the easier tasks were treated by the physiotherapists with rhetorical questions. The second type of discourse consisted of the physiotherapists directing the patients' attention to their problems, and of the patients' and caregivers' initiatives leading to conversation about the patients' problems. The patients understood the significance of the test performance for their life at home in varying ways. The results of this study showed that successful counseling calls for physiotherapists to develop dialogic communication skills to help patients in coconstructing their home exercise together with their social network.

Adult↗

PubMed2005

A topodiagnostic investigation on body lateropulsion in medullary infarcts.

Body lateropulsion may occur without signs of vestibular dysfunction and vestibular nucleus involvement. The authors examined 10 such patients with three-dimensional brainstem mapping. Body lateropulsion without limb ataxia reflected an impairment of vestibulospinal postural control caused by a lesion of the descending lateral vestibulospinal tract, whereas body lateropulsion with limb ataxia was probably the consequence of impaired or absent proprioceptive information caused by a lesion of the ascending dorsal spino-cerebellar tract.

Ataxia↗

PubMed2000

Romberg's sign: development, adoption, and adaptation in the 19th century.

In the first half of the 19th century, European physicians-including Marshall Hall, Moritz Romberg, and Bernardus Brach-described loss of postural control in darkness of patients with severely compromised proprioception. Romberg and Brach emphasized the relationship between this sign and tabes dorsalis. Later, other neurologists evaluated the phenomenon in a broader range of neurologic disorders using a variety of simple but increasingly precise and sensitive clinical tests. Although now known as Romberg's sign, among neurologists in the late 19th century this phenomenon was sometimes credited to Romberg, sometimes to both Brach and Romberg, and sometimes discussed without attribution.

History, 19th Century↗

PubMed1995

Spatial orientation in the lamprey. II. Visual influence on orientation during locomotion and in the attached state

The responses of attached lampreys to homogeneous visual stimulation and the role of visual stimuli in orientation during locomotion were investigated. Experiments were performed by video recording the responses of intact and lesioned animals to illumination. The following results were obtained. 1. In lampreys attached with their sucker mouth to the bottom of the aquarium, illumination of one eye evoked several possible motor responses (ordered after mean latency): (a) movement of the illuminated eye downwards, and the contralateral eye upwards; (b) rotation of the body around the longitudinal axis, with the illuminated side tilting downwards; (c) deviation of the caudal part of the anterior dorsal fin in the contralateral direction (away from the light); and (d) flexion of the neck and body towards the side of illumination. 2. Illumination of one eye in attached lampreys often resulted in detachment and subsequent movement in a direction away from the light source (negative phototaxis). This response was not related to the degree of roll tilt before detachment, so the negative phototaxis does not appear to be a consequence of the vestibular stimulation. 3. Negative phototaxis was also seen during locomotion: lampreys turned through 180 ° when they approached a brightly illuminated area. Photostimulation also affected their orientation in the transverse plane during swimming. Illumination of one eye from the side induced a roll movement, so that the illuminated side tilted downwards and the dorsum of the lamprey became turned towards the light. This is similar to the 'dorsal light response' of fish and shows that vision also plays a role in postural control in lampreys. 4. The behaviour of blinded animals differed strikingly from that of intact ones. Whereas intact animals preferentially swam close to the bottom, along horizontal trajectories, blinded animals showed episodes of continuous swimming upwards, near the water surface. During horizontal swimming, their orientation in the transverse plane remained normal, with the dorsal side up.

Journal Article↗

PubMed1997

Variability of leg kinematics in free-walking crayfish, Procambarus clarkii, and related inter-joint coordination

The inter-joint coordination in leg 4 of the crayfish Procambarus clarkii was investigated while they travelled freely along straight paths. Video analysis of the kinematics of the leg's three-dimensional motion, combined with a statistical method based on conjugate cross-correlation functions, showed stable inter-joint coordination in the leg kinematics. In particular, the inter-joint coordination involved a strong movement in the distal mero-carpopodite (M-C) joint occurring between the movements of the proximal thoraco-coxopodite and coxo-basal joints; thus, the leg extended during the swing phase and flexed during the stance phase. This synchronisation was mainly independent of global changes in the locomotor pattern induced by variation in speed or contralateral inter-leg coupling which occurred during free walking. The main changes in inter-joint coordination were found to be related to the appearance of a biphasic flexion/extension movement during each stroke of the step cycle when the leg retracted far backwards. This movement was observed more frequently in large animals and was therefore possibly related to changes in postural control. The functional role of this distal M-C joint movement in the leg motion is discussed.

Journal Article↗

PubMed2000

Regulation of neurotrophin signaling in aging sensory and motoneurons: dissipation of target support?

A hallmark of senescence is sensorimotor impairment, involving locomotion and postural control as well as fine-tuned movements. Sensory and motoneurons are not lost to any significant degree with advancing age, but do show characteristic changes in gene-expression pattern, morphology, and connectivity. This review covers recent experimental findings corroborating that alterations in trophic signaling may induce several of the phenotypic changes seen in primary sensory and motoneurons during aging. Furthermore, the data suggests that target failure, and/or breakdown of neuron-target interaction, is a critical event in the aging process of sensory and motoneurons.

Aging↗

PubMed1995

Cerebellar afferents to neuroendocrine cells: implications for adaptive responses to simulated weightlessness.

The hypothalamo-neurohypophyseal system as well as the autonomic nervous system is involved in homeostatic responses associated with changes in head position and orthostatic reflex. The responses induced by body tilt on earth are thought to be attributed to changes in inputs from baroreceptors, vestibular organs and proprioreceptors that are normally required for postural control. The information from these organs is sent to the hypothalamus which thereby influences both neuroendocrine and autonomic systems as well as various kinds of emotional behavior. Our findings showing the fastigial input to the hypothalamus suggested that the FN plays a significant role in these homeostatic responses through its connections with the brain stem and the hypothalamus. Figure 4 shows the input-output organization among the hypothalamus, cerebellum and brain stem, described in detail in sections III to V. This hypothesis may help to account for the autonomic and endocrine disorders often observed in weightlessness.

Adaptation, Physiological↗

PubMed2002

Effects of transcutaneous electrical nerve stimulation (TENS) on non-pain related cognitive and behavioural functioning.

An extensive search through nine electronic bibliographic databases (PubMed, Cochrane Library, Web of Science, ERIC, PsychINFO, Psyndex, Cinahl, Biological Abstracts, Rehabdata) was performed in order to review the effects of Transcutaneous Electrical Nerve Stimulation (TENS) on non-pain related cognitive and behavioural functioning. Eight studies were identified on neglect due to stroke, six studies on Alzheimer's disease (AD), one study on aging, and two studies on coma due to traumatic brain injury. The results of the various studies revealed that TENS has a variety of effects. These consist of enhancement of somatosensory functioning, visuo-spatial abilities and postural control in neglect, improved memory, affective behaviour and rest-activity rhythm in AD and acceleration of awakening in coma. Effectiveness of TENS is discussed in relation to various stimulation parameters: duration, frequency, pulse width and intensity. It is argued that arousal may underlie the beneficial influence of TENS in various conditions. Finally, suggestions are offered for future research.

Adolescent↗