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PubMed2006

Perception of angular displacement without landmarks: evidence for Bayesian fusion of vestibular, optokinetic, podokinesthetic, and cognitive information.

The perception of angular displacement during self turning is generally based on a combination of redundant signals from different sources. For example, during active turning in a visually structured environment devoid of landmarks, podokinesthetic, vestibular, and optokinetic velocity signals are fused and integrated over time to yield a unitary percept of the ongoing change in angular position ('podokinesthetic' refers to proprioceptive and corollary signals related to leg and foot movement). Previously we have shown that the fusion of two of these afferents improves perceptual accuracy and reliability in comparison to when only one is available. For example, with only a single modality available, slow rotations are perceived to be significantly larger than fast ones, whereas the combination of two modalities greatly reduces this difference. These observations spurred the hypothesis that displacement perception results from a weighted average of bottom-up (sensory) signals and top-down signals (a priori knowledge or expectation), with the weight of the latter decreasing the more sensory information is available. We now ask (1) whether the accuracy of angular displacement estimation can be further improved if it can draw on all three sensory modalities instead of only two, and (2) whether bottom-up sensory and top-down a priori information is combined for displacement estimation in a statistically optimal way. To this end 12 healthy subjects (Ss) standing on a turning platform surrounded by a rotatable optokinetic pattern were exposed to 6 different sensory conditions: pure podokinesthetic (P), vestibular (V), or optokinetic (O) stimulation, and combined podokinesthetic-vestibular (PV), vestibular-optokinetic (VO), or podokinesthetic-vestibular-optokinetic (PVO) stimulation. Stimuli had constant angular velocities of either 15, 30, or 60 degrees /s. Subjects were to press a signal button when they felt that angular displacement had reached a previously instructed magnitude (150-900 degrees ). In agreement with earlier observations, the combination of two sensory signals improved the accuracy of displacement perception by reducing both the variance of subjects' displacement estimates and their dependence on turning velocity. Adding a third sensory signal (condition PVO) led to a further reduction of variance and almost eliminated the effect of velocity. We show that these experimental results are compatible with a probabilistic fusion mechanism based on Bayes' law. This mechanism would operate on logarithmic representations of turning velocity and proceed in two stages. A first stage fuses all available bottom-up information to create a unitary representation of the velocity signalled by the different sensory modalities. A second stage then fuses this sensory information with top-down a priori information; the latter creates a bias in favour of a 'default velocity' that grows as the uncertainty of the sensory information increases. Our experimental data agree with the relation between (1) the variance of displacement estimates and (2) their modulation by velocity predicted by this scheme.

Adolescent↗
PubMed2005

Self-perception of physical competences in preadolescent overweight Chinese children.

OBJECTIVE: To compare self-perceptions of physical competences in overweight and in normal weight preadolescent Chinese children. DESIGN: Cross-sectional study. SETTING: Three primary schools and a university hospital in Hong Kong. SUBJECTS: A total of 634 children, comprising 558 (462 normal weight, 96 overweight) aged 8-12 y randomly sampled from three primary schools, and 76 similar age overweight children recruited from the community for a diet and exercise intervention programme. MEASUREMENTS: Height, weight and percentage body fat were measured. Self-perceptions of physical competences were determined by Physical Self-Descriptive Questionnaire (PSDQ). Corresponding actual physical competences were measured by physical fitness tests. RESULTS: Overweight children perceived themselves to have significantly more body fat than normal weight children, with poorer appearance, sports competence, endurance, coordination, flexibility, overall physical self-concept and self-esteem, but to be no less healthy, no less physically active and no less strong. Overweight children performed less well than normal weight children in measures of endurance, coordination and flexibility but better in strength. Poor self-perception of physical competences appeared only partly related to deficiencies in actual physical competences. CONCLUSION: Overweight children have poorer self-perception of their physical competences but do not perceive themselves to be less strong, healthy or physically active than normal weight children. Exercise programmes for overweight children could be more effective if designed with the knowledge of these self-perceptions.

Body Composition↗
PubMed1979

Failure of oral L-histidine to influence appetite or affect zinc metabolism in man: a double-blind study.

L-Histidine, 4 g/day in gelatin capsules, was administered orally to eight normal volunteers for 2 weeks in a double-blind, balanced, crossover study with 2 weeks of placebo treatment. Body weight, serum and urinary zinc and histidine concentrations, as well as subjective ratings of appetite, taste and smell perception, and food intake were monitored. L-Histidine therapy had no significant effect on appetite, taste and smell perception, food intake, or body weight. Similarly, no effects were observed on total serum zinc, albumin-bound zinc or alpha 2-macroglobulin-bound zinc concentrations, or on urinary histidine excretion. Serum histidine concentrations increased with therapy. Urinary zinc excretion was increased significantly after 1 week, but not after 2 weeks of L-histidine therapy. It can be concluded that oral L-histidine, at the dose used, has no value as an anorectic agent.

Adult↗
PubMed2000

Changes in breathing during observation of effortful actions.

Respiration and heart rates were recorded in normal subjects watching effortful actions produced by an actor in front of them. Subjects remained immobile throughout. Two experiments were performed. In experiment 1, subjects watched a weight-lifting performance, either static or dynamic, with increasing weights. In experiment 2, they watched a walking/running performance on a treadmill moving at increasing speed. In both experiments, no change was found in observers' heart rate. By contrast, consistent changes were found in respiration rate. These changes tended to follow the exercise rhythm of the actor, specially during accelerated running (from 2.5 to 10 km/h) where respiration rate increased linearly with speed of the treadmill. Average maximum increase ranged between 25 and 30% above resting rate. This finding demonstrates activation of central mechanisms related to action performance during observation of effortful actions. It could represent a basis for understanding and imitating actions performed by other people.

Adult↗
PubMed2006

The relationship of asymmetric weight-bearing with postural sway and visual reliance in stroke.

Due to motor and sensory deficits in individuals with stroke, we proposed that they must compensate for these impairments during standing with greater dependence on vision. In addition, we hypothesized that asymmetric weight-bearing, which occurs following stroke, is related to increased postural sway and those with greater asymmetry will have greater reliance on vision. Twenty-eight individuals with stroke and 28 healthy older adult controls stood quietly with eyes open (EO) or closed on a force platform while postural sway was quantified by centre of pressure measures and weight-bearing asymmetry was calculated from vertical ground reaction forces. To determine the influence of vision on postural sway, a visual ratio (eyes open/eyes closed (EC)) was calculated for the sway measures. The results demonstrated that individuals with stroke had greater visual dependence for the control of postural sway velocity in the medial-lateral (ML), but not anterior-posterior (AP) direction, compared to controls. Further, we found that greater asymmetry was moderately related to increased medial-lateral sway for the individuals with stroke. Contrary to predictions, those individuals with stroke with mild asymmetry had greater visual dependence than those with more severe asymmetry.

Case-Control Studies↗
PubMed2003

Selective use of visual information signaling objects' center of mass for anticipatory control of manipulative fingertip forces.

The present study examines whether visual information indicating the center of mass (CM) of an object can be used for the appropriate scaling of fingertip forces at each digit during precision grip. In separate experiments subjects lifted an object with various types of visual cues concerning the CM location several times and then rotated and lifted it again to determine whether the visual cues signaling the new location of the CM could be used to appropriately scale the fingertip forces. Specifically, subjects had either no visual cues, visual instructional cues (i.e., an indicator) or visual geometric cues where the longer axis of the object indicated the CM. When no visual cues were provided, subjects were unable to appropriately scale the load forces at each digit following rotation despite their knowledge of the new weight distribution. When visual cues regarding the CM location were provided, the nature of the visual cues determined their effectiveness in retrieval of internal representations underlying the anticipatory scaling of fingertip forces. Specifically, when subjects were provided with visual instructional information, they were unable to appropriately scale the forces. More appropriate scaling of the load forces occurred when the visual cues were ecologically meaningful, i.e., when the shape of the object indicated the CM location. We suggest that visual instructional cues do not have access to the implicit processes underlying dynamic force control, whereas visual geometric cues can be used for the retrieval of the internal representation related to CM for appropriate partitioning of the forces in each digit.

Adolescent↗
PubMed2000

Gender differences in cognitive abilities at 2 years in ELBW infants. Extremely low birth weight.

Gender differences in cognitive abilities exist for children born at term. For very preterm infants uncertainty exists regarding the presence and extent of such differences and their relationship to perinatal brain injury and neurological impairment. This study examined gender differences in cognitive abilities in a cohort of 336 extremely low birth weight (ELBW) infants at 2 years corrected age. Infants were classified as at low or high perinatal risk at birth according to four perinatal risk factors. A subgroup of 33 neurologically impaired infants was identified. Outcome at 2 years was measured by the overall General Quotient (GQ) on the Griffiths scale and its five subscale scores. Female ELBW children were superior to male ELBW children by 4.1 GQ points (95% CI 1.0, 7.1). If the impaired subgroup was excluded, the difference in GQ was 3.2 points (95% CI 0.4, 5.6), and this difference was predominantly due to female infants being superior in the hearing and speech subscale (6.0 points, 95% CI 2.6, 9.5). These differences were relatively independent of perinatal risk status. Gender differences in the Griffiths GQ for ELBW infants are similar to expected differences for term infants and are unlikely to cause substantial bias in interpreting outcome studies for ELBW infants, unless these involve tests of specific cognitive abilities such as language.

Auditory Perception↗
PubMed2005

Long-term homocysteine exposure induces alterations in spatial learning, hippocampal signalling and synaptic plasticity.

Abnormally high levels of homocysteine (HCY) have been linked to neurodegenerative diseases, but it remains unclear whether this is the cause or effect of degenerative processes. Here, we investigated the effects of prolonged HCY exposure on cognitive abilities and physiological parameters by injecting rats daily with either 20 or 200 mg/kg HCY over a period of up to 14 weeks. Notwithstanding a significant weight reduction in the 200 mg HCY group, HCY-exposed animals did not show a behavioural deficit when tested repeatedly (in weeks 1, 3, 5, 7 and 13) in a reference memory version of the water maze. Unexpectedly, some improvement in repeated reversal learning was observed in HCY exposed animals compared to controls. Pre-treatment with HCY for 3 weeks before water maze training did not uncover any cognitive alterations. Increased plasma concentrations of HCY were revealed only for the 200 mg HCY group after 14 weeks of injections, but no evidence for DNA damage was obtained. Immunocytochemically, HCY was detected in the brain after 14 weeks of treatment (both 20 and 200 mg/kg), but not after 5 weeks. Bidirectional changes in basic synaptic transmission and long-term potentiation of hippocampal CA1 pyramidal cells were observed at 5, 7 and 14 weeks in both HCY groups, indicative of complex, multifactorial time- and concentration-dependent changes. Overall, it is concluded that healthy adult rats are able to cope with continuous exposure to HCY. While HCY affects growth and neuronal excitability, this does not precipitate into an immediate impairment of cognitive function.

Animals↗
PubMed2004

Recovery of standing balance in postacute stroke patients: a rehabilitation cohort study.

OBJECTIVE: To identify and interrelate static and dynamic characteristics of the restoration of quiet standing balance in a representative sample of stroke survivors in the Netherlands during their inpatient rehabilitation. DESIGN: Exploratory study using an inception cohort with findings related to reference values from healthy elderly persons. SETTING: Rehabilitation center. PARTICIPANTS: Thirty-seven inpatients (mean age, 61.6y; mean time poststroke, 10.0wk) with a first hemispheric intracerebral infarction or hematoma who were admitted to retrain standing balance and walking. INTERVENTION: Individualized therapy. MAIN OUTCOME MEASURES: Center of pressure fluctuations were registered under each foot and in the sagittal and frontal planes separately by using a dual-plate force platform. The first balance measurements took place as soon as patients were able to stand unassisted for at least 30 seconds as well as 2, 4, 8, and, 12 weeks later. Quiet standing was assessed under 4 conditions: with and without a visual midline reference, with the eyes closed, and while performing a concurrent arithmetic task. RESULTS: The stroke patients showed excessive postural sway and instability, particularly in the frontal plane, compared with reference values. Frontal plane balance was, however, also most responsive to the effects of balance training and recovery (P<.001). The degree of visual dependency for frontal plane balance control showed a significant reduction in time (P<.02). Weight-bearing asymmetry, which was most pronounced in patients with disturbed sensibility or ankle clonus, diminished considerably during the first 4 weeks of the follow-up period (P<.02). Yet, a substantial degree of weight-bearing asymmetry persisted during the 8 weeks thereafter, and it continued to be aggravated by attentional distraction (P<.001). During the same period, static asymmetry (ie, the degree of pes equinovarus loading at the paretic side) and dynamic asymmetry (ie, the extent to which compensatory ankle moments are applied at the nonparetic side) did not show normalization at all, although motor selectivity of the paretic leg improved by 1 stage on the 6-stage Brunnstrom scale (P<.001) and the independency level of balance and walking skills improved by 2 points on the 6-point Functional Ambulation Categories (P<.001). CONCLUSIONS: Balance recovery in postacute stroke inpatients is characterized by a reduction in postural sway and instability as well as by a reduction in visual dependency, particularly with regard to frontal plane balance. These restoration characteristics may be important factors underlying the relearning of independent standing and walking abilities. The clear lack of normalization for measures reflecting static and dynamic aspects of postural asymmetry suggests that the functional improvements in balance and gait must be more related to other mechanisms than to the restoration of support functions and equilibrium reactions of the paretic leg.

Adult↗
PubMed1988

Body image and eating behavior in adolescent girls.

To determine attitudes toward body weight and shape and eating and weight control practices among adolescent girls, an anonymous questionnaire was administered to 854 adolescent girls and young women aged 12 through 23 years who were seen in a military adolescent outpatient clinic. Overall, 67% were dissatisfied with their weight, and 54% were dissatisfied with their body shape. Dissatisfaction with weight and shape varied positively with increasing body weight but not with increasing age. Binge eating had occurred in 30.4%, and weight control behavior, such as dieting, fasting, vomiting, and stimulant, laxative, and diuretic use, had occurred in 38.2%, 30.7%, 8.5%, 9.5%, 3.3%, and 6.2%, respectively, varying positively with increasing weight. Thirty-six percent of those adolescent girls who saw themselves as overweight desired an inappropriate weight loss, and 61% of these, who desired an excessive loss, exhibited an increased prevalence of weight control behaviors and were less likely to believe that they had an eating problem. Dissatisfaction with body weight and shape, and eating behaviors, such as dieting, binge eating, fasting, and vomiting, are common in adolescent girls, many of whom are attempting weight control without an accurate perception of what is normal.

Adolescent↗
PubMed2006

Peripheral neuropathy and object length perception by effortful (dynamic) touch: a case study.

The spatial extents of hand-held objects can be perceived nonvisually by wielding them. This ability of effortful or dynamic touch to exploit the mass moments of an object to perceive its length was evaluated with a 40-years old right-handed woman with surgically treated Arnold-Chiari Type 1 Malformation and cervical syrinx. At the time of the experiment she presented with loss of discriminative touch in the left arm but no comparable sensory deficits in the right arm or the lower extremities. She could neither identify objects in her left hand nor tell that they were in the hand while manipulating them. She could, however, grasp an object tightly and wield it on request. In the experiment she wielded weighted rods of 45, 60, and 80cm length about the wrist. There were two main results. First, her nonvisual perception of rod length by the insensate left arm scaled systematically with rod moment of inertia. The scaling matched that of the intact right arm and the nondominant arm of haptically unimpaired controls tested with rods of similar dimensions. Second, her right arm was superior in accuracy and reliability than her insensate left arm and was equal to or better than the dominant arm of the control group on key measures of nonvisual length perception. The first result was evaluated in respect to the notions of numb touch and differences in the neural bases of discriminative and effortful touch. The second result was discussed in terms of contralateral cortical enhancement by deafferentation.

Adult↗
PubMed2006

Impact of cognitive task on the posture of elderly subjects with Alzheimer's disease compared to healthy elderly subjects.

The aims of this study were to analyze the effects of cognitive task on static posture in Alzheimer's disease (AD) and in healthy elderly (HE) subjects and to evaluate whether those effects were greater in AD subjects than in HE subjects. We performed a posturographic analysis on 13 subjects with mild AD (mean age, 79.7+/-5.1 years, Mini-Mental State Examination scores between 18 and 23) and on 17 HE subjects (mean age, 78.5+/-4.4 years). After watching a video sequence, the subjects were asked to maintain a stable upright posture while standing on a force platform. Then, the postural sway was measured during the following two conditions: (1) quiet standing and (2) both standing and answering questions about the video sequence. We were interested in the center of pressure (CoP) area and path. For each group, the single task was compared to the dual task for the CoP area and path. We also compared the variability of both CoP area (variation of the CoP area between the single and the dual task) and path (variation of the CoP path between the single and the dual task) between the two groups. We showed that there was no significant difference between the single and the dual task in HE subjects concerning the CoP area and path, in contrast to the AD group, and that variability of both the CoP area and path were significantly greater in the AD subjects than in the HE subjects. This finding may contribute to the risk of falls in AD patients.

Accidental Falls↗
PubMed1975

Albinism and auditory function in the laboratory mouse. II. Effects of acoustic priming and cross-fostering.

Albino (c/c) and nonalbino (+/c and +/+) congenic C57BL/6J mice were examined for the effects of acoustic prestimulation (priming) on audiogenic seizures. While no genotypic-specific effects were noticed 1 day after priming, major effects were observed in separate groups of mice tested 5 days after priming. The c/c mice were most susceptible to audiogenic seizures, and no differences were observed between +/c and +/+ mice. While cross-fostering did not change this relationship, it provided protection from acoustic trauma is considered inconclusive because of the interaction of innate- and priming-induced audiogenic seizures in the +/c and c/c mice.

Age Factors↗
PubMed2004

Postural stabilization from fingertip contact: I. Variations in sway attenuation, perceived stability and contact forces with aging.

In this study, we compared the ability of young (n=10, 19-32 years) and older subjects (n=35, 60-86 years) to use fingertip contact as a balance aid during quiet stance under various conditions to determine whether aging would influence contact strategies. Experimental trials (duration, 60 s) included two visual conditions (vision; no vision), three fingertip contact conditions (no touch; smooth touch; rough touch) and two support surface conditions (firm; foam). In trials with contact, participants were required to maintain a light contact with their right index fingertip on an instrumented touch-plate. Subjects were not constrained to exert minimal contact force, although they were aware that the touch-plate was not designed for physical support. From displacements of the centre of foot pressure (COP), mean sway amplitude (MSA) was computed in the anterior-posterior (COP(AP)) and medio-lateral (COP(ML)) directions. Subjective estimates of stability were also obtained by asking participants to rate perceived stability on a visual analog scale in each condition. Mean normal force (FN) and mean resultant tangential force (F(TAN)) were computed from contact force data applied on the touch plate. In both age groups, touch conditions had a substantial effect on MSA in the AP direction under both support surface conditions, with reductions averaging between 40-55% when touch was allowed. Reductions in the ML direction, though less important (8-12% on average), were nevertheless highly significant, especially in the older subjects when standing on the foam. In the two groups, vision and texture had only marginal impact on MSA computed on both support surfaces. Contrasting with sway measurements, stability ratings were highly influenced by visual conditions in both age groups. Only in conditions of deficient support (foam surface) and absent vision did the perceived effect of touch exceed that of vision. Age had a major impact, however, on contact forces deployed during trials with touch. While individuals in the young group typically produced forces of <1 N (mean FN, 0.32+/-0.15 N) to achieve postural stabilization, older subjects tended to use higher, though not too excessive, contact forces (mean FN, 1.21+/-0.75 N) under the same conditions. From these findings, we conclude that the ability to use contact cues from the fingertip as a source of sensory information to improve postural stability is largely preserved in healthy older adults. The increase in contact force deployed by older individuals to achieve postural stabilization is interpreted as a compensatory strategy to help overcome age-related loss in tactile sensation, an issue that will be further addressed in a companion paper.

Adult↗
PubMed2005

Differences in preferred reference frames for postural orientation shown by after-effects of stance on an inclined surface.

This study reports a postural after-effect of leaning that follows a period of stance on an inclined surface with eyes closed. This leaning after-effect maintained the body-to-surface relationship as if subjects still stood on the incline. We examined the incidence and robustness of the leaning after-effect in 51 healthy subjects. The location of the center of pressure (CoP) under the feet and the alignment of the trunk and legs were measured before, during and after blindfolded subjects stood on a 5 degrees toes-up inclined surface for 2.5 min. When the surface was inclined, all subjects stood with their trunk and legs aligned near to gravity-vertical, similar to the alignment adopted in the pre-incline period. When the surface returned to horizontal in the post-incline period, there was a continuum of postural alignment strategies across subjects. At one extreme, subjects leaned forward, with an average trunk lean near 5 degrees . The leaned posture decayed exponentially toward baseline postural alignment across a period of up to 5 min. At the other extreme, subjects did not lean in the post-incline period, but instead, stayed aligned near upright with respect to gravity. Subjects were highly consistent in their post-incline postural behaviors upon repeated testing over days to months and across different directions of surface inclination. Our results suggest that individuals have well-established, preferred, sensory strategies for controlling postural orientation when vision is not available. Subjects who leaned in the post-incline period appear to depend more on the geometry of the support surface as a reference frame and to rely more on proprioceptive information to extract kinematic relationships, whereas subjects who did not lean appear to depend more on gravity as a reference frame and to rely more on sensory information related to forces and load.

Adaptation, Physiological↗
PubMed2001

The role of action in postural preparation for loading and unloading in standing subjects.

The main purpose of the present study has been to find an answer to the question: Can the subject generate anticipatory postural adjustments (APAs) when a predictable postural perturbation occurs in the absence of a voluntary action? Answering this question would allow us to distinguish between two competing hypotheses on the relation between APAs and voluntary movements. One hypothesis considers both APAsigma and voluntary "focal" movements different peripheral patterns associated with a single control process, while the alternative hypothesis considers them outcomes of two parallel control processes. Healthy subjects performed series of loading and unloading trials that included: (1) catching a falling load onto another load held in extended hands; (2) catching a falling load onto a tray attached to the trunk; (3) allowing a falling load to hit another load out of the extended hands, causing an unloading; and (4) releasing a load held in extended hands by a voluntary shoulder movement. In series 1, precautions were taken to avoid possible small hand movements prior to the impact of the falling load. Available visual information on the trajectory of the falling load was manipulated. In all conditions, except when the subject's eyes were closed, APAs were seen with patterns that were adequate for counteracting expected perturbations. Quantitative electromyographic indices of APAs depended on the availability of visual information and particular methods of introducing postural perturbations despite the fact that the magnitude of the perturbation was always the same. Our findings support a hypothesis that control processes resulting in APAs can be different from control processes associated with focal voluntary movements.

Adult↗
PubMed2002

Somatosensory and skin temperature disturbances caused by infarction of the postcentral gyrus: a case report.

Somatosensory functions are subdivided into 2 large groups: the elementary somatosensory functions, which consist of light touch, pain, thermal sensation, joint position sense, and vibration sense, and the intermediate somatosensory functions, which include 2-point discrimination, tactile localization, weight, texture, and shape perception. In this report, we describe a patient with somatosensory dysfunction after infarction of the postcentral gyrus. On physical examination a month after the onset of the infarction, voluntary movements were skillful, and both the elementary and intermediate somatosensory functions were disturbed in the right hand. The patient also displayed a decrease in the skin temperature of the right hand. The sensory-evoked potential in response to electrical stimulation of the right median nerve was normal, and brain MRI showed that the infarction was located in the posterior half of the left postcentral gyrus. These findings suggested that the lesion was situated at areas 1 and 2, and that area 3b was preserved. Thermography revealed that the skin temperature of the right hand was decreased predominantly on the ulnar side, and that recovery from cooling with ice water was delayed. By comparing the results of our patient with a case report that showed no disturbance of the elementary somatosensory functions with a localized lesion in the postcentral gyrus, we suggest that area 1 participates in the elementary somatosensory functions and that skin temperature may be controlled somatotopically in the somatosensory cortex.

Cerebral Infarction↗