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The control of balance of 20 healthy subjects under visual stimulation was quantitavely evaluated using a force platform. Three different visual stimuli were administered using a head-mounted display and CAVE. CAVE was significantly more effective in perturbing balance in one stimulus and HMD was significantly more effective in another.
Short (SL), medium (ML), and long (LL) latency EMG responses of leg muscles were recorded after perturbation of stance by means of a sudden toe-up tilt of a movable platform. 56 healthy children varying in age between 14 months and 15 years were investigated. All three responses were present when children were able to stand on the recording platform. The SL-response in the triceps surae muscle, which corresponds to the mono- and oligo-synaptic spinal stretch reflex, showed a decreasing latency up to the age of 5 years. This reflects the increasing peripheral nerve conduction velocity. The ML-response in the triceps surae muscle, which as the SL-response has no stabilizing effect in this experiment, showed somewhat delayed maturational changes. The LL-response in the relaxed anterior tibial muscle helps to restore upright posture even in the youngest children. Its maturational changes in terms of latency by far exceed the range that can be explained by the increase of peripheral and spinal conduction velocities. Its mechanisms of maturation, besides the biophysical optimalization of a polysynaptic network, may include learning in terms of selecting the shortest pathways by way of synaptic potentiation within structures involved in the supposedly transcortical pathway of the LL-response. Qualitative observations made during the trials showed that the pattern of postural adaptation changed with age, suggesting the development of additional intersegmental mechanisms.
In order to define the acute effects of a moderate quantity of alcohol on balance, related to the vestibular function, vestibulo-ocular reflex (VOR) test, caloric test and dynamic posturography (EquiTest) were performed. Ten healthy male volunteers aged 19-27 average 22.8) years old imbibed 1.5 ml whisky (alcohol content 43%) per kilogram of body weight within 5 min. Blood alcohol level (BAL) was measured before administration and then after 30, 90, and 150 min. Equilibrium examinations were performed immediately after each blood sample was taken. At the highest alcohol level, significant reductions were found in VOR gain, in the maximum slow-phase velocity of the caloric test and in the equilibrium score of the sensory organization test in condition 5, when compared with those before drinking. In some typical cases, the subjects' response in all tests were most disturbed at the time when the highest alcohol level was measured. From our results, we conclude that a moderate quantity of alcohol affects not only the oculomotor system but also the vestibular system. Furthermore, it was suggested that one of the reasons for postural instability after drinking alcohol may be reduced vestibular function.
Certain patients with balance disorders report a 'visual vertigo' in which their symptoms are provoked or aggravated by specific visual contexts (e.g. supermarkets, driving or movement of objects). In order to determine the causes of visual vertigo (VV), we assessed symptoms, anxiety and the influence of disorienting visual stimuli in 21 such patients. In 17 out of 21 patients, a peripheral vestibular disorder was diagnosed. Sixteen bilateral labyrinthine-defective subjects (LDS) and 25 normal subjects served as controls. Questionnaire assessment showed that the levels of trait anxiety and childhood motion sickness in the three subject groups were not significantly different. Reporting of autonomic symptoms and somatic anxiety was higher than normal in both patient groups but not significantly different between LDS and VV patients. Handicap levels were not different in the two patient groups, but the reporting of vestibular symptoms was higher in the VV than in the LDS group. The experimental stimuli required subjects to set the subjective visual vertical in three visual conditions: total darkness, in front of a tilted luminous frame (rod and frame test) and in front of a large disc rotating in the frontal plane (rod and disc test). Body sway was also measured in four visual conditions: eyes closed, eyes open, facing the tilted frame and during disc rotation. In psychophysical and postural tests, both LDS and VV patients showed: (i) a significant increase in the tilt of the visual vertical both with the static tilted frame and with the rotating disc; and (ii) an increased postural deviation whilst facing the tilted frame and the rotating disc. The ratio between sway path with eyes closed and eyes open (i.e. the stabilizing effect of vision) was increased in the LDS, but not in VV patients, compared with normal subjects. In contrast, the ratio between sway path during disc rotation and sway path during eyes open (i.e. the destabilizing effect of a moving visual stimulus) was increased in the VV patients but not in LDS. Taken together, these data show that VV patients have abnormally large perceptual and postural responses to disorienting visual environments. VV is not related to trait anxiety or a past history of motion sickness. The results indicate that VV emerges in vestibular patients if they have increased visual dependence and difficulty in resolving conflict between visual and vestibulo-proprioceptive inputs. It is argued that treating these patients with visual motion desensitization, e.g. repeated optokinetic stimulation, should be beneficial.
1. The electrophysiological properties of two pairs of identified serotonin-containing neurons in the fifth thoracic (T5) and first abdominal (A1) ganglia of the lobster, Homarus americanus, were studied with the use of intracellular recording methods. Intracellular dye injection combined with immunocytochemistry verified the neurochemical status of the recorded neurons. 2. The serotonin-containing neurons usually are spontaneously active at 0.5-1.0 Hz and produce large, overshooting action potentials with a prominent after-hyperpolarization. The action potentials appear to be generated by a pacemaking mechanism endogenous to the cells. Extracellular recordings from thoracic connectives and from second thoracic roots show that action potentials from the cells in A1 and T5 are propagated rostrally along their axons and invade axon collaterals that innervate neurohemal organs in the second thoracic roots and the pericardial organs. These observations suggest that these serotonin-containing cells may function in part as important neurosecretory cells in the lobster. 3. Members of the pairs of serotonin-containing cells are not synaptically connected. They receive prominent inhibitory inputs in the form of inhibitory postsynaptic potentials (IPSPs), which exhibit discrete size classes and probably arise from several sources. Most IPSPs are temporally synchronized among the two pairs of serotonin-containing cells. 4. The serotonin-containing cells respond to stimulation of postural command fibers, with flexion command fibers exciting and extension command fibers inhibiting the cells, suggesting that these cells are a part of the postural flexion circuitry. 5. Intracellular activation or inhibition of the serotonin-containing cells has no effect on the spontaneous readout of postural motor programs recorded from motor nerve roots. Coactivation of the serotonin-containing cells and command fibers, or inhibition of the serotonin-containing cells while activating command fibers, however, shows that the cells act as "gain-setters," modulating the interaction between command inputs and motoneuron outputs. 6. About 24% of the motor neuron units analyzed are influenced by the serotonin-containing cells. There is a bias toward facilitation of the readout of flexion motor programs, particularly with stimulation of strong and moderate flexion command fibers. 7. The serotonin-containing cells in T5 and A1 ganglia are hypothesized to serve two functions, one tonic and the other phasic, in modulating behavioral output in lobsters. Tonic firing of the cells should result in a sustained release of serotonin from central and peripheral sets of nerve terminals, which, in turn, could influence peripheral and central targets of the amine.(ABSTRACT TRUNCATED AT 400 WORDS)
Thirty-one patients with severe adolescent idiopathic scoliosis were evaluated preoperatively by computerized dynamic posturography. Curve type, magnitude and spine balance were measured radiographically. In four girls, a very mild vestibular dysfunction was observed on the sensory organization analysis, and three of them had a horizontal shift of more than 2 cm; a disbalance was observed in only three other patients among the 27 patients with normal posturography. These results suggest that abnormalities in the sensory systems are not involved in the etiology of severe adolescent idiopathic scoliosis. The vestibular dysfunction detected in the four patients was most probably the result of disbalance and not the cause of the disease.
Biomechanical modeling estimated that trunk muscle activity during various tasks could be reduced by 1-14% without the loss of spine stability when a lumbosacral orthosis (LSO) is worn [Cholewicki, J., 2004. The effects of lumbosacral orthoses on spine stability: what changes in EMG can be expected? Journal of Orthopedic Research 22, 1150-1155]. The present study experimentally tested these theoretical predictions in an unstable sitting task. This task required subjects to balance on a seat supported by a plastic hemisphere (slashed circle=30cm) and placed on a force plate that tracked the center of pressure (CoP). The average CoP velocity quantified subjects' performance. Healthy subjects (12 males, 11 females) balanced for 20s in 3 trials performed with and without the LSO in random order. EMG was recorded bilaterally from rectus abdominis (RA), external oblique (EO), thoracic (TES) and lumbar erector spinae (LES), and expressed as the % of maximum voluntary activation (%MVA). There was no difference in the balance performance with and without the LSO (p=0.13). However, EMG averaged across the trials was significantly lower in the LSO, as compared to the No LSO condition, for TES (5.8+/-3.2 vs. 6.4+/-3.7%MVA, p=0.02) and LES (3.7+/-1.5 vs. 5.9+/-3.9%MVA, p=0.01). No significant differences were present in the abdominal muscle activity. These results agree with earlier spine modeling simulations, which predicted the greatest reduction in muscle activity due to LSO to occur in TES and LES. It was hypothesized that such a reduction in muscle co-contraction could benefit patients with low back pain, who exhibit elevated muscular activity during postural tasks such as walking, standing and sitting.
The purpose of this study was to investigate the effect of different dopamine receptor antagonists on the function of proprioceptive reflex mechanisms involved in the regulation of stance and gait. Haloperidol as preferential D2 and the 'pure' dopamine D2 receptor antagonist sulpiride significantly reduced the level of the reflex response in the gastrocnemius muscle following backward perturbation. Flupentixol, however, which in addition blocks D1 receptors, had no effect on compensatory gastrocnemius EMG responses. Furthermore, neither the peripherally acting dopamine D2 receptor antagonist domperidon nor the sedative diazepam had any significant influence on this functionally essential reflex mechanism. None of the drugs tested had a significant effect on the tibialis anterior responses elicited following forward perturbation. It is concluded that the reduced stretch sensitivity of the gastrocnemius (but not that of the tibialis anterior) during perturbations of stance described for parkinsonian patients corresponds to these results and arises from an impaired function of central dopamine D2 receptors.
In order to investigate the contribution of proprioceptive input to maintaining an upright position, stabilometry via 100-Hz vibratory stimulation applied to the Achilles tendon was studied and analyzed with respect to area, length and power spectra according to the method of fast Fourier transform (FFT). Twenty-one young medical students were analyzed in this study. When vibration was applied, the body sway was significantly greater than that of control in area and length with both eyes open and closed. There was a significant increase of total power in both the lateral (X) and antero-posterior (Y) directions with the eyes closed. With the eyes open, an increase was found only in the antero-posterior direction. The frequency band indicating the maximum spectrum did not shift. Significant increases in power spectra were found in the frequency range of more than 2 Hz in both two directions with the eyes closed. It was concluded that a vibration given to the Achilles tendon provoked a pronounced high frequency body sway especially in the antero-posterior direction when visual information was nullified, and that proprioceptive information may have a minor role compared with visual information.
The goal of the present study was to determine the properties of the somatosensory stimulus that alter its temporal coupling to body sway. Six standing subjects were tested while touching a metal plate positioned either directly in front of or lateral to the subject. In each condition, the plate moved 4 mm at 0.2 Hz in either the medial-lateral (ML) or anterior-posterior direction (AP). The results showed that coupling between body sway and touch plate movement was strongest when the touch plate moved in a direction along the longitudinal axis of the arm. Coupling strength was weaker when the touch plate moved perpendicular to the longitudinal axis of the arm. The results consistently show that a radial expansion stimulus was more effective than a lamellar-type stimulus at the fingertip. Moreover, somatosensory information from a surface is interpreted in terms of the orientation of the contact limb and the potential degrees of freedom available through its movement.
There is, not only from an economic perspective, a continuous search for surgical and anaesthetic procedures that allow out-patient surgery to be conducted. Reliable estimators of the patient's street fitness are of the utmost importance. Balancing capacity is one aspect that should be considered. Clinical methods like Romberg's are subjective and imprecise. Dynamic posturography comprises a movable support surface and visual surround that are either stable or referenced to the patient's sway, with eyes open or closed. In this study the recovery from propofol anaesthesia was studied in 8 patients who underwent surgery for minor microlaryngoscopic procedures. Dynamic posturography who performed before, and 2 and 4 h after cessation of anaesthesia. All patients who were awake had normal balancing ability already at 2 h after anaesthesia. Further studies may supply additional information of other aspects of discharge after anaesthesia.
The purpose of this experiment was to determine the interaction between visual and vestibular information during the transition from quiet standing to the completion of a forward step. Six subjects were asked to take one step forward at the sound of an audio tone, with their eyes open or closed, and terminate the step in a standing position. During stimulation trials, galvanic vestibular stimulation (GVS) was delivered 1500 ms before the auditory cue. GVS was delivered at an intensity three-fold that of each subject's quiet stance threshold with either stimulus right, left or no stimulation. Force data were collected from three forceplates for the calculation of centre of pressure (CoP), and kinematic data were used to calculate centre of mass (CoM) and body trajectories. In quiet stance all subjects responded to the GVS perturbation by demonstrating upper body segment roll and whole body sway towards the anode electrode. Unexpectedly, in the presence of vision during quiet stance, the upper body roll response was not attenuated, even though the CoP sway patterns were reduced when vision was available. During the initiation phase of the step, despite ongoing GVS stimulation, there were no significant effects seen in CoM, CoP or upper body roll responses. During step execution, however, both CoM displacement and upper body roll demonstrated significant effects and both responses were significantly reduced when subjects' eyes were open. Analysis of the medio-lateral CoP integrals also indicated a strong stimulation effect between conditions late in the execution phase, which were largely attenuated with vision. The results suggest that the importance of visual and vestibular information varies depending on the phase of the task. In addition, the different integration between visual and vestibular input during quiet standing suggests a dual role for vestibular information. We propose that vestibular information in quiet standing has a role in maintaining whole body postural stability, as well as playing an integral role in the alignment of the body segments in preparation for proper movement execution. Vision was demonstrated to differentially attenuate these responses based on the phase of the task. Thus, visual and vestibular information appear to be integrated differently across the different phases of a forward-stepping task.
The aim of the current study was to further investigate a recently proposed "sensory re-weighting" hypothesis, by evoking anterior-posterior (AP) body sway using visual stimuli during sway-referencing of the support surface. Twelve healthy adults participated in this study. Subjects stood on the platform while looking at a visual scene that encompassed the full horizontal field of view. A sequence of scene movements was presented to the subjects consisting of multiple visual push/pull perturbations; in between the first two push/pull sequences, the scene either moved randomly or was stationary. The peak-squared velocity of AP center-of-pressure (COP) was computed within a 6 s window following each push and pull. The peak-squared velocity was lowest for the push/pull sequence immediately following the random moving scene. These results are consistent with the sensory re-weighting hypothesis, wherein the sensory integration process reduced the contribution of visual sensory input during the random moving scene interval. We also found evidence of habituation to moving scene perturbations with repeated exposure.
This study was carried out in order to test the hypothesis of a right hemisphere dominance in the visual control of body balance. Eight healthy adults were subjected to a self-regulated lateral balance task, performed while sitting on a rocking platform. Four visual conditions were tested: open eyes with normal vision, closed eyes in the dark, left visual field-right hemisphere and right visual field-left hemisphere. Head and support displacements in the roll plane were recorded by means of an optoelectronic system. Two main results emerged from this study: (1) head stabilization in space was much more efficient in the left visual field-right hemisphere condition than in the three other visual conditions, and (2) although vision played an important role in the body stability whatever the anatomical level, there was no right hemisphere dominance at the pelvic level. A clear right hemisphere dominance was thus demonstrated as regards the visual contribution to head stabilization in space.
One hypothesis for the generation of spatially oriented arm movements by the central nervous system is that a desired joint position is determined by the ratio of the tensions of agonist and antagonist muscles. According to this hypothesis, the transition between equilibrium states should be solely a function of the contraction time of the motor units and the mechanical properties of the arm. We tested this hypothesis in intact and deafferented rhesus monkeys by holding the forearm and measuring the accelerative transient after release of the forearm and by directly measuring the time course of the increase in torque during the movement. Both methods indicated an average time of 400 msec for attaining peak torque in a movement with a duration of 700 msec. In addition, by displacing the arm from its normal trajectory during the movement, we observed that the arm returned neither to the initial nor to the final equilibrium positions, but to points intermediate between them. We conclude that the processes underlying trajectory formation must be more complex than a simple switch between one equilibrium position and another.
A model is introduced for the motor program which controls final position. The first part of the model relates the biomechanical properties of the muscles to the EMG activities of the extensor and flexor muscles and thereby generates quantitative predictions for the relationships between the EMGs, final position, external forces, muscle stiffness, and muscle tension. To the extent that comparable data exist, the model is shown to give correct quantitative predictions. When only qualitative comparisons can be made, the model is consistent with the data in the literature. The model is complete and can be tested quantitatively in detail in the future. An equivalent circuit for the neural network that innervates the muscles is given. It is shown to have the advantages of making the programming of final position simple to either compute or look up in a table. In addition, new situations, such as adapting to a force, or an unusual viewing angle, lead to very simple changes in the basic program in terms of the equivalent circuit.
This study assessed whether stationary auditory information could affect body and head sway (as does visual and haptic information) in sighted and congenitally blind people. Two speakers, one placed adjacent to each ear, significantly stabilized center-of-foot-pressure sway in a tandem Romberg stance, while neither a single speaker in front of subjects nor a head-mounted sonar device reduced center-of-pressure sway. Center-of-pressure sway was reduced to the same level in the two-speaker condition for sighted and blind subjects. Both groups also evidenced reduced head sway in the two-speaker condition, although blind subjects' head sway was significantly larger than that of sighted subjects. The advantage of the two-speaker condition was probably attributable to the nature of distance compared with directional auditory information. The results rule out a deficit model of spatial hearing in blind people and are consistent with one version of a compensation model. Analysis of maximum cross-correlations between center-of-pressure and head sway, and associated time lags suggest that blind and sighted people may use different sensorimotor strategies to achieve stability.
UNLABELLED: Pusher syndrome is an interesting disorder of balance in patients with encephalic lesions characterized by the peculiar behavior of actively pushing away from the non-hemiparetic side and resisting against passive correction, with a tendency to fall toward the paralyzed side. The role of vestibular system on the pushing behavior is not clear. AIM: To evaluate horizontal semicircular canal function in patients with Pusher syndrome, using caloric and rotation tests. STUDY DESIGN: Observational prospective. MATERIAL AND METHOD: We evaluated 9 inpatients with stroke and Pusher syndrome at the neurological unit of HCFMRP-USP. We applied neurological and neuropsychological exams, NIHSS, Scale for contraversive pushing (SCP), caloric and rotation tests. RESULTS: We evaluated 9 patients (5 men) with mean age of 71.8 +/- 5.9 and mean NIHSS of 18.33. Three patients presented contralateral directional preponderance on caloric test and we found four patients with directional preponderance on analysis of the slow phase velocity of rotation test response. CONCLUSION: Our findings indicate that a dysfunction of semicircular canals does not seem to be relevant for the clinical manifestations of the Pusher syndrome.