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PubMed1990

[From posture to initiation of movement].

Purposeful motor acts are subjected to two contradictory constraints. One is to move one or several body segments toward a goal, the other is to stabilize other segments in order to maintain posture and equilibrium. One of the major tasks of the central nervous system is to coordinate posture and movement. Human posture is built up from the superposition of several "modules' from the ground to the head. Each module, tied to the next one by muscles, has its proper central and reflex regulation which permits to maintain its position in relation to the underlying one. In addition, a global regulation of posture is apparent (postural tone). Equilibrium is maintained under static conditions when the center of gravity projects onto the ground within the supporting surface (feet). Sensory error detecting signals (visual, labyrinthine, proprioceptive) are correcting, through a feedback loop, the reference regulated value according to a "postural' body schema based on "metric' and "dynamic' inputs. Corrections are continuous (and slow) or discontinuous and phasic through a repertoire of synergies allowing fast corrections. During movement performance, posture and equilibrium are stabilized by "anticipatory postural adjustments'. Some are aimed at maintaining the equilibrium notwithstanding the displacement of body segments due to the movement; others stabilize one or several segments such as the head, the trunk or the arm, which serve as reference value for the calculation of the movement trajectory and for the accurate performance of the movement. The anticipatory adjustments are learned during childhood or during training for specific tasks. The adaptative networks built up for a given movement are then controlled by the movement related command signals. The central organization of these anticipatory postural adjustments relies on central brain structures involved in movement execution and movement organization. Deficit is seen in spastic patients, to some extent in cerebellar patients. Basal ganglia and premotor areas, including the supplementary motor area, are of importance for coordination between posture and movement. This suggests that one of their function might be to stabilize posture during movement performance in order to ensure precise reaching of the goal. A specific pathology of the anticipatory postural adjustments should thus be considered.

Animals↗
PubMed1994

Clinically silent dysfunction of dorsal columns and dorsal spinocerebellar tracts in hereditary spastic paraparesis.

Hereditary spastic paraparesis (HSP) is a neurodegenerative disorder, of which progressive spastic paraparesis is the clinical hallmark. Given the neuropathological evidence of degeneration of pyramidal tracts, dorsal columns, and dorsal spinocerebellar tracts, it is surprising that sensory symptoms are so indistinct compared to motor symptoms. We investigated the involvement of peripheral conduction and spinal proprioceptive pathways by nerve conduction studies, somatosensory evoked potentials of the median and tibial nerves, and quantitative assessment of the vibration perception thresholds of the hands and feet respectively in 32 patients suffering from HSP and healthy control groups. We did not find peripheral conduction abnormalities in HSP patients. Log-transformed vibration perception thresholds of the feet were abnormal in 13/32 HSP patients and in 0/64 controls (p < 0.00001), while tibial nerve somatosensory evoked potentials were abnormal in 20/32 patients and in 1/17 controls (p = 0.00001). The values for the upper extremities were within normal limits for nearly all subjects. In the HSP group, the neurophysiological disturbances did not correlate significantly with duration or severity of the disease, when age was controlled for, except for median nerve SSEP latency, which was affected by severity (p = 0.0072). We conclude that neurophysiological methods detected proprioceptive, subclinical abnormalities in several HSP patients, which may reflect degeneration of the dorsal columns, and/or dorsal spinocerebellar tracts. Since we found no correlation with several disease variables, the fact that not all HSP patients displayed these abnormalities may be caused by anatomical variations in proprioceptive pathways, rather than by phenotypical heterogeneity.

Action Potentials↗
PubMed2006

Barosensory cells in the nucleus tractus solitarius receive convergent input from group III muscle afferents and central command.

Some neural mechanism must prevent the full expression of the baroreceptor reflex during static exercise because arterial blood pressure increases even though the baroreceptors are functioning. Two likely candidates are central command and input from the thin fiber muscle afferents evoking the exercise pressor reflex. Recently, activation of the mesencephalic locomotor region, an anatomical locus for central command, was found to inhibit the discharge of nucleus tractus solitarius cells that were stimulated by arterial baroreceptors in decerebrated cats. In contrast, the effect of thin fiber muscle afferent input on the discharge of nucleus tractus solitarius cells stimulated by baroreceptors is not known. Consequently in decerebrated unanesthetized cats, we examined the responses of barosensory nucleus tractus solitarius cells to stimulation of thin fiber muscle afferents and to stimulation of the mesencephalic locomotor region, a maneuver which evoked fictive locomotion. We found that electrical stimulation of either the mesencephalic locomotor region or the gastrocnemius nerve at current intensities that recruited group III afferents inhibited the discharge of nucleus tractus solitarius cells receiving baroreceptor input. We also found that the inhibitory effects of both gastrocnemius nerve stimulation and mesencephalic locomotor region stimulation converged onto the same barosensory nucleus tractus solitarius cells. We conclude that the nucleus tractus solitarius is probably the site whereby input from both central command and thin fiber muscle afferents function to reset the baroreceptor reflex during exercise.

Action Potentials↗
PubMed1996

Balance after stapedectomy: the measurement of spontaneous sway by posturography.

Sway was measured by static posturography in 25 patients undergoing stapedectomy, 16 first-side and nine second-side operations. Measurements were taken pre-operatively and at 1 week and 6 months after surgery, 25 age-matched controls were also tested. In both the first and second side groups, sway was greater at 1 week after surgery than pre-operatively when relying on vestibular function alone (P = 0.01 first-side, 0.05 second-side, 0.01 both sides taken together). By 6 months, sway measurements were no longer significantly different from pre-op or control values. Thus, it appears that there is a measurable increase in patients' sway following stapedectomy but this is well compensated by visual and proprioceptive information, and resolves fully with time. Patients undergoing a second side stapedectomy do not appear to fare worse than those undergoing first-side surgery.

Humans↗
PubMed1993

Sensory interaction posturography in patients with benign paroxysmal positional vertigo.

BPPV (benign paroxysmal positional vertigo) is a very common peripheral vestibular disturbance. The dysfunction becomes manifest mainly by vertigo and typical nystagmus. However, the vestibulospinal reflex (VSR) can also be disturbed. This can be shown by the SPGIII (static posturography type III), which is a platform technique evaluating 'sensory interaction' in a way comparable to that of the Equi-test. Half the patients with BPPV show disturbed posturographic results. By interfering with the sensory input of vision and/or proprioception, the separate contribution of each input can be evaluated. Different 'formulae' are seen, from complete normal results, through 'overall' formulae, i.e. an undifferentiated influence in all test-conditions, to specific formulae, where we find 'eye-closure' and 'head retroflexed'-effect and so-called 'vestibular formulae'. These formulae are an expression of the different degrees of compensation achieved by the centres and especially of the 'substituting' compensation by vision and proprioception. These results confirm that posturography does not provide a typical results-pattern, thus the type of peripheral vestibular disorder cannot be diagnosed by it alone. The results give functional information on how the standing position is achieved in these patients with a disturbed VSR-input. The several formulae prove that indeed different compensatory patterns are possible, as has been shown by experiments on vestibular compensation.

Adolescent↗
PubMed1986

The magician's forceps phenomenon in exotropia under general anaesthesia.

Prifinium bromide was administered for eight weeks to three patients with exotropia. Under general anaesthesia active discharges from the lateral rectus muscles were demonstrated by electromyography. When a slight adductive force was applied to the straight or the master eye, active discharge from the lateral rectus of the associate eye disappeared in all patients, and this eye moved in the direction of orthophorisation. The discharge reappeared when the master eye was released from the forced adduction. From these results the authors concluded that proprioception is involved in the magician's forceps phenomenon discovered by Mitsui in exotropic patients in 1978.

Adolescent↗
PubMed1978

Muscle stretch receptor hypersensitization in spasticity. Inapproprioception, Part III.

The author's concept of Inapproprioception, which accounts for athetoid movements in terms of defective proprioceptive feedback (i.e., distortion of afferent signals representing limb position) is extended here to explain spasticity in cerebral palsy was well. Descending activation of gamma efferents supplying hypertonic muscles may be excessive, leading to hypersensitization of stretch receptors in those muscles (the exact distribution of muscles affected varying with the individual). The result is exaggerated reflex activation of alpha motoneurons in response to the slightest muscle stretch. Even passive tension due to gravitational forces, which is inescapable, results in excessive impulse discharge from sensitized stretch afferents and thus leads to reflex contractions simply in response to shifts in body position. The affected muscles shorten to a length corresponding to the elevated level of reflexly originating motoneuron discharge, manifesting excessive tone even in the contracted state. The distribution of hypertonicity thus induced usually follows a predictable pattern and can be modified using slow passive stretch of hypertonic muscles to relax them, followed by facilitated voluntary contraction to strengthen weak antagonists, and progressing to functional reciprocal usage of agonists and antagonists to achieve proper muscle balance. Application of this procedure leads to improved posture, balance and ambulation in subjects with spastic cerebral palsy.

Adolescent↗
PubMed1994

[Disorders of walking in elderly subjects: towards new concepts].

While gait disorders directly related to a muscular, skeletal neurological defect are easily recognized, others, which we address here, appear to result from some unknown and mysterious mechanism. Gait disorders in elderly patients cannot be conceived as a simple impairment in muscle, tendon or joint effectors but must be assessed in relation to defective central programmation or dysfunctioning synergy. Posture is the result of a series of successive reflex reactions, and locomotion itself is the result of a series of sequential stimulations and inhibitions originating in the spinal generator controlled by supraspinal centres. Obviously, in man, cortical and subcortical activation is essential as is the activity of the limbic system and the associative zones, together with the basal gangia and the cerebellum. Peripheral proprioception accelerates consciousness of information originating in the muscles, tendons and joints; vestibular and visual input adds further, though redundant, information. Advanced methods of quantifying posture and walking offer a new approach to the analysis of gait disorders. The Bessou locometer analyzes physiological senescence leading to an inconscient strategy which decreases the speed and length of each step. This mechanism might be explained by the aging process leading to non-necrotic cell failure without any specific lesion, vascular for example. Another method is the ELITE system (Elaboratore de Immagini Televisive). This system evaluates the way the subject modelizes and reconstructs his environment. Interesting results have been obtained with postural imbalance induced by visual stimulations.

Aged↗
PubMed1993

Sensorimotor and perceptual function of muscle proprioception in microgravity.

Adaptive properties of the human proprioceptive systems were studied during the French-Soviet orbital flight (Aragatz mission, December 1988). The present space experiment investigated the hypothesis that the modifications of both biomechanical and physiological conditions occurring under microgravity involve considerable reorganization of body perception and postural control. The proprioceptive information originating in muscles is known to contribute, together with visual, vestibular, and sole cutaneous information to postural regulation. Moreover, by specifically activating the proprioceptive channel, muscle vibration is able to elicit both illusory movement sensations and postural responses. This experimental tool was used in microgravity in order to test various aspects of muscle sensory function. Ankle flexor and extensor vibration was applied under different experimental conditions. Quantitative analysis of motor responses was carried out on leg muscle EMG, goniometric, and kinesigraphic recordings. Joystick recordings and astronauts' comments were used to describe the kinaesthetic sensations. The main results were as follows: 1) Under microgravity, the sensitivity of muscle receptors remains unchanged. 2) During the flight, the tonic vibration reflexes (TVR) increased significantly in flexor muscles, which exhibited a sustained tonic activity. 3) The whole-body postural responses normally induced by ankle flexor muscle vibration were suppressed, whereas they remained unchanged or were only reduced when vibrations were applied to the ankle extensor muscles. In all cases, the postural response velocity decreased. 4) A disfacilitation of the vibration-induced postural illusions was observed to occur during long-term exposure to microgravity. These illusions became atypical however. For example: body lift illusion could be induced by tibialis anterior muscle vibration, whereas it was never induced in the controls. The characteristics of the illusory body movements described under normal gravity can be restored by artificially increasing the axial foot support forces during the flight. In conclusion, these data suggest that a functional reorganization of the proprioceptive information processing occurs in microgravity, affecting both perceptual and motor aspects of behavior. It is possible that these proprioceptive adaptations may be partly attributable to the new whole-body propulsive foot functions imposed by exposure to weightlessness and to the adaptation of motor behavior to the third dimension of space.

Adaptation, Physiological↗
PubMed2001

Evidence that spinal segmental nitric oxide mediates tachyphylaxis to peripheral local anesthetic nerve block.

BACKGROUND: Tachyphylaxis to sciatic nerve blockade in rats correlates with hyperalgesia. Spinal inhibition of nitric oxide synthase with N(G)nitro-L-arginine methyl ester (L-NAME) has been shown to prevent hyperalgesia. Given systemically, L-NAME also prevents tachyphylaxis. The action of L-NAME in preventing tachyphylaxis therefore may be mediated at spinal sites. We compared systemic versus intrathecal potency of L-NAME in modulating tachyphylaxis to sciatic nerve block. METHODS: Rats were prepared with intrathecal catheters. Three sequential sciatic nerve blocks were placed. Duration of block of thermal nocifensive, proprioceptive and motor responses was recorded. We compared spinal versus systemic dose-response to L-NAME, and examined effects of intrathecal arginine on tachyphylaxis. An additional group of rats underwent testing after T10 spinal cord transection. In these rats duration of sciatic nerve block was assessed by determining the heat-induced flexion withdrawal reflex. RESULTS: L-NAME was 25-fold more potent in preventing tachyphylaxis given intrathecally than intraperitoneally. Intrathecal arginine augmented tachyphylaxis. Spinalized rats exhibited tachyphylaxis to sciatic block. CONCLUSION: The increased potency of intrathecal versus systemic L-NAME suggests a spinal site of action in inhibiting tachyphylaxis. Descending pathways are not necessary for the development of tachyphylaxis since it occurs even after T10 spinal cord transection. Thus tachyphylaxis, like hyperalgesia, is mediated at least in part by a spinal site of action.

Anesthetics, Local↗
PubMed2001

Cortical representation of whole-body movement is modulated by proprioceptive discharge in humans.

Previous studies have revealed the influence of ongoing sensory discharge on modulating the central representation of muscle afferents from individual limbs. In the present study, we explored the potential for such modulatory influence on the afferent discharge arising from induced whole-body movement. Vestibular and somato-sensory inputs arise from such whole-body movement. The convergence of these two modalities is important in motor control, especially for the maintenance of postural stability. We hypothesised that transmission of proprioceptive and vestibular information to the cortex would be reduced as a result of muscle-spindle discharge in knee extensor muscles. Perturbation-evoked responses (PERs), recorded from central scalp electrodes (C3, CZ, C4), were evoked through rapid translations of subjects who were seated in a chair on a movable platform. PERs were recorded during passive linear translations alone and preceded by vibration of the patellar tendon. The PER was characterised by a slow, negative potential peaking at approximately 150 ms (N150) following displacement of the chair. The amplitude of the PER was reduced following vibration to 56% of the control. Such reduction of PERs was comparable to the attenuation of somatosensory evoked potentials and soleus H-reflex magnitudes from tibial-nerve stimulation. We conclude that muscle-spindle discharge in knee extensor muscles leads to gating of both of these afferent pathways. These results have potential implications to the understanding of the CNS control of stability during ongoing movement.

Adult↗
PubMed1995

Control variables and proprioceptive feedback in fast single-joint movement.

Sensorimotor mechanisms were studied on the basis of kinematic and electromyographic data as well as the static torque developed by the muscles as a function of joint angle. The latter relationship is known as the torque/angle characteristic. Fast single-joint movement may result from a shift in this characteristic and a change in its slope. Such movements were studied at the wrist in 9 normal and 1 deafferented subject. After training to flex the wrist to a target, subjects repeated the same movements but in random test trials movements were opposed by the load generated by linear position feedback to a torque motor. At the end of the loaded trials, the load was suddenly removed. In the second experiment, subjects made wrist movements to the target that were opposed by the load and, on random test trials, the movements were not loaded. In these test trials, the wrist arrived in a static position outside the target zone. In both experiments, subjects were instructed not to correct errors. The final torque/angle characteristics specified in the movements were reconstructed on the basis of the static wrist positions and torques before and after unloading. Normal subjects made movements by shifting the position of the torque/angle characteristic and by increasing its slope. If subjects indeed maintained the same pattern of control variables (descending commands), the same final position of the characteristic would be reproduced from trial to trial regardless of load perturbations. This assumption of equifinality was tested by comparing the final position of the wrist in nonloaded movements with that after removal of the load in loaded movements. Equifinality was observed in normal subjects. Movements in the deafferented subject were also associated with a shift of the torque/angle characteristic and a change in its slope. However, she was unable to consistently reproduce its final position. In spite of muscle coactivation, her maximal stiffness was lower than in normal subjects. In the absence of vision, the subject made movements with the load by increasing the slope of the characteristic instead of by shifting its position far enough. Load perturbation affected her final wrist position (inequifinality), which may reflect the presence of a significant hysteresis of the characteristic as a result of the absence of stretch reflexes. The deficits following deafferentation presumably result from the destruction of biomechanical and sensorimotor mechanisms including the ability of control variables to specify the positional frame of reference for afferent and descending systems.

Adult↗
PubMed1995

Early onset cerebellar ataxia with retained tendon reflexes: a clinical, electrophysiological and computed tomographic study.

Fourteen patients of Early Onset Cerebellar Ataxia with retained tendon reflexes (EOCA) were prospectively evaluated clinically, electorphysiologically and with CT scan. Their age and duration of symptoms were 18.6 +/- 8.3 years and 7.8 +/- 5.1 years respectively. High consanguinity (91.7%) and positive family history (76.9%) suggested autosomal recessive inheritance. Apart from cerebellar signs and brisk knee jerks in all, other important findings were abnormal ocular movements (mostly impaired saccades) in 92.8%, Babinski's sign (78.6%), brisk ankle jerks (64.3%), spasticity in lower limbs (50%) and impairment of proprioceptive sensations (50%). Neuropsychological tests, done in 12 patients, were abnormal in all. Abnormalities of electroneuromyographic studies were universal, motor conduction parameters (85.7%) being more affected than sensory (78.6%). One or more modalities of evoked potentials were abnormal in 71.4%, that of brainstem auditory evoked response being most frequent (50%), followed by posterior tibial somatosensory evoked potential (SSEP) (46.1%) and median SSEP and visual evoked potential (30.8% each). CT scan (n = 12) showed atrophy of brainstem (91.7%), cerebellar hemisphere and/or vermis (83.3%) and cerebral cortex (33.3%). There was no correlation between the duration of disease and degree of disability or abnormalities of nerve conduction and CT parameters. The rationality of the diagnosis of this recently recognised entity of 'EOCA' in Indian context is discussed.

Adolescent↗
PubMed1977

Biologic laws governing functions of muscles that move the mandible. Part II. Condylar position.

A model to quantify muscle response to occlusal contacts is useful in developing an understanding of the mechanism by which the occlusion programs muscle function. A knowledge of how the occlusion programs muscle function enables the dentist to develop manipulative skills of the mandible which are necessary for diagnosis and effective occlusal treatment. This article presents complicated neuromuscular responses (reflexes) to occlusal contacts in an oversimplified way and with analogies so that the clinical significance of these neuromuscular reflexes in diagnosis and treatment can be more easily understood.

Biomechanical Phenomena↗
PubMed1990

Homo quintadus, computers and ROOMS (repetitive ocular orthopedic motion stress).

Inherent conflict exists between computer systems and ocular physiology of Homo quintadus. Adverse ocular side effects of excessive saccades, excyclotorsion, supraduction, excessive field-of-fixation usage, capitas extension, astigmatic changes, otostatic reflex mismatching, and needless orthopedic malfunctions are imposed upon computer operators. Although the orthopedic dysfunctions are commonly grouped under the heading of Repetitive Strain Injuries (RSI), the inextricable linkage to poor ocular-neurological function argues for postulation of a broader schema entitled Repetitive Ocular Orthopedic Motion Stress (ROOMS). Concepts of good tool usage, total tactile familiarity, total proprioceptive familiarity, and visual cone-of-comfort clash with the installed-equipment base and indicate need for an integrated computer work station to facilitate near covisualization of screen/keyboard and to afford freedom-of-choice for optimal hand/eye synchronicity. The advocacy of computer operators' needs by user-welfare groups, universities, labor unions, and government agencies are portents for achieving genuine improvements.

Biological Evolution↗
PubMed1984

A discussion of the dynamic illegible "E" test: a new method of screening for aminoglycoside vestibulotoxicity.

Although aminoglycoside antibiotics have been successful in controlling infections, the side effects of these drugs include vestibulotoxicity that can be irreversible. In a patient with intact visual and proprioceptive systems, the effects can be compensated for, but in a patient with impairment of one of these systems, loss of vestibular function can be devastating. There is little if any agreement in the literature about how to monitor patients undergoing therapy with these drugs. A reading test is described. It uses the ability of the vestibulo-ocular reflex to stabilize an image during head movement. The test is quantified using change in visual acuity with head movement to monitor damage to the vestibular system. Patients with loss of vestibular function are incapable of performing the test. Some evidence points to the test being more sensitive than standard caloric irrigations. We propose that it be used to monitor patients receiving aminoglycoside antibiotics.

Adult↗
PubMed1973

The role of proprioceptive afferents in the control of respiratory muscles.

Building largely on the results of previous studies of motor control in respiration the role of proprioceptive control of respiratory movements is discussed with particular reference to the significance of the following points: (i) The co-activation of fusimotor and alpha motoneurons in load compensation and in the control of velocity and force of the respiratory movements. (ii) The convergence onto the same intercostal spindle of fusimotor fibres for respiratory movements and for postural activity. (iii) The difference between proprioceptive control of intercostal muscles on the one hand and the diaphragm on the other, and of the control of the phrenic motoneuron pool exerted by intercostal proprioceptors. (iv) The cerebellar control both of the fusimotor-alpha balance between the indirect drive of the intercostal motoneurons and of the responsiveness of the phrenic motoneuron pool to respiratory and reflex influences. (v) Results suggesting spinobulbar reflex effects on the control of rate and depth of respiration from muscle and joint receptors of the thoracic wall.

Cerebellum↗