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PubMed1992

Role of Ia muscle spindle afferents in post-contraction and post-vibration motor effect genesis.

Experiments carried out on 14 human subjects showed that long-lasting involuntary tonic motor responses occurred after the offset of muscle vibration (70 Hz, 0.5 mm, duration 30 s). These post-vibratory biceps and triceps brachii motor responses were compared with the motor responses observed in the same subjects after performing an isometric contraction of the same duration, i.e., post-contraction responses, or the so-called 'Kohnstamm phenomenon'. The results show the existence of close similarities between these two types of motor after-effect, particularly as regards the muscle sites where they develop, their amplitudes and their temporal patterns (latencies and offset times). Neither type of excitatory post-effect can be elicited by co-contracting or co-stimulating two antagonist muscles at the same frequency. Lastly, visual stimulation can cause both types of motor response to switch from one muscle to its antagonist. Comparative analysis of the spindle proprioceptive activities recorded in response to either vibration or isometric contractions suggests that these motor after-effects may both result from the fact that the spindle afferents from agonist and antagonist muscles are asymmetrically activated in these two particular situations.

Electromyography↗
PubMed1996

Three-dimensional analysis of nystagmus induced by neck vibration.

The role of dorsal neck proprioceptive inputs to vestibular compensation was investigated in 11 patients with unilateral vestibular dysfunction. Subjects had neither spontaneous nystagmus nor disequilibrium, indicating that they were well compensated. Vibratory stimulation to the dorsal neck produced marked nystagmus. All subjects showed horizontal component directed towards the contralateral side of the lesion. Vertical and torsional components of the nystagmus were exhibited by 10 and 7 subjects, respectively. These results indicate that the neck vibration caused a discompensation in vestibularly well compensated subjects after unilateral dysfunction. In addition, the influence of neck afferent on the vestibulo-ocular reflex pathways, not only of the horizontal, but also the vertical systems, is discussed.

Eye Movements↗
PubMed1995

Phasic cutaneous input facilitates locomotor recovery after incomplete spinal injury in the chick.

1. Walking and swimming of hatchling chicks was videotaped before hemisection of the left thoracic cord and thereafter at regular intervals, for up to 2 wk. With the use of kinematic techniques, movements of the left knee and ankle were quantified to assess recovery of the ipsilateral leg during walking and swimming trials. To study the effects of exteroceptive (cutaneous) feedback in the absence of limb loading, one group of animals was also provided with cutaneous stimulation during swimming in the form of neutrally buoyant tubes that only contacted the foot during the retraction (extension) phase of the swim cycle. 2. One day after hemisection, for both swimming and walking, the left knee failed to extend normally, and the ankle joint remained hyperextended. During walking, all chicks adopted an asymmetric gait, whereas during swimming the left leg remained retracted and motionless. 3. Over the next 2 wk, knee extension and ankle flexion during walking recovered to normal preoperative values, but neither measure returned to preoperative values during swimming trials. However, when chicks were provided with phasic cutaneous stimulation during swimming trials, they showed improvements in leg motion as soon as 5 days after hemisection. Temporary removal of the cutaneous stimulation during swimming (5 days after hemisection) resulted in reduced limb action. However, 14 days after hemisection, the improvement in limb motion was retained even when the cutaneous stimulation was not provided. 4. Improvement in leg motion after swim training with phasic cutaneous stimulation took the form of increased extension of the limb during retraction. Possible neurophysiological mechanisms for this behavior include reflex reinforcement of limb extensor activity in response to cutaneous stimulation of the foot. Repeated exposure to phasic stimulation during swimming trials results in a permanent alteration in limb action. Thus increased cutaneous afferent inputs, even in the absence of limb loading, can facilitate locomotor recovery after spinal cord injury.

Animals↗
PubMedDate not supplied

The control of head movements during human balance corrections.

The assumption that the CNS regulates head stability during human balance corrections is explored in this review (an outgrowth of discussions initiated during the Head/Neck meeting held in Vail, Colorado, USA, July 1995). Two major questions were considered. First, how do the vestibulocollic (VCR) and cervicocollic (CCR) reflexes interact with intrinsic mechanical properties of the head neck system to control head position during balance corrections? Second, how is this interaction affected by factors such as vestibular loss, aging, and changes in behavioral goals or central set? The authors conclude that head velocities observed during balance corrections depend to a large extent on the movements of the head-neck mass-viscoelastic system whose properties could be altered by cocontracting the neck muscles. For experiments involving stance perturbations, much of the corrective response in neck muscles appeared to be triggered by trunk and leg proprioceptive signals, and a major role for the VCR was not established. Evidence consistent with a role for the vestibular system was found in other experimental paradigms in which the head was perturbed directly. In these paradigms the VCR modulates the amplitude of functionally stabilizing responses and damps mechanically induced instability of the head and neck.

Adult↗
PubMed1997

Postural perturbations: new insights for treatment of balance disorders.

This article reviews the neural control of posture as understood through studies of automatic responses to mechanical perturbations. Recent studies of responses to postural perturbations have provided a new view of how postural stability is controlled, and this view has profound implications for physical therapy practice. We discuss the implications for rehabilitation of balance disorders and demonstrate how an understanding of the specific systems underlying postural control can help to focus and enrich our therapeutic approaches. By understanding the basic systems underlying control of balance, such as strategy selection, rapid latencies, coordinated temporal spatial patterns, force control, and context-specific adaptations, therapists can focus their treatment on each patient's specific impairments. Research on postural responses to surface translations has shown that balance is not based on a fixed set of equilibrium reflexes but on a flexible, functional motor skill that can adapt with training and experience. More research is needed to determine the extent to which quantification of automatic postural responses has practical implications for predicting falls in patients with constraints in their postural control system.

Biomechanical Phenomena↗
PubMed2002

Under-rated neuro-otological symptoms: Hoffman and Brookler 1978 revisited.

In 1978, Hoffman and Brookler published an article in The Laryngoscope to challenge prevailing views on the lack of diagnostic power of certain symptoms often reported by patients to neuro-otologists. Some of these 'under-rated neuro-otological symptoms' include complaints of non-rotational dizziness, blurred and double vision, and the development of visual motion hypersensitivity in patients with balance disorders. In this review, I revisit these visual symptoms in the light of new findings from our laboratory. Double vision due to skew eye deviation can indeed occur in peripheral vestibular disease when there is a large, acute peripheral imbalance of vestibular function. It is more frequent and severe in brain stem disease. In both cases, it is explained by disruption of the torsional vestibular ocular reflex. It is usually assumed that damage to the otolith underlies the emergence of skew diplopia, but recent evidence shows that the vertical canal system is likely to be partly responsible as well. The other 'under-rated symptom' revisited here is what patients describe as dizziness when watching moving objects or whilst walking in visually busy surroundings such as supermarkets. Recent work has shown that this 'visual vertigo' emerges in patients who, in addition to suffering from a vestibular disorder, have increased visual dependence. Visual dependence denotes subjects who preferentially use vision, as opposed to vestibular or proprioceptive input, for spatial orientation and postural control. We do not know as yet what makes some vestibular patients become extremely visually dependent. However, we have provided evidence for Hoffman and Brookler's impression that visually triggered complaints should not be summarily dismissed, as they often point to an underlying vestibular disorder.

Diplopia↗
PubMed2005

Otolith deprivation induces optokinetic compensation.

According to the multisensory integration theory vestibular, optokinetic and proprioceptive inputs act in concert to maintain a stable retinal image of the visual world. Yet, it remains elusive to what extent the otolith organs contribute to this process and whether a specific loss of otolith input is compensated for. Here we investigated the compensatory eye movements in tilted mice, which lack otoconia because of a mutation in otopetrin 1. Tilted mice showed very small displacements of the eyes in the orbit during static roll paradigms, suggesting the absence of functional otolith organs. Independent of head position with respect to gravity, the gain and phase lead of angular vestibuloocular reflex of tilted mice were decreased and increased, respectively (frequencies 0.2 to 1 Hz and peak accelerations 8 to 197 degrees /s2, respectively). Furthermore, lack of otolith input increases the dependency of the vestibular system on stimulus frequency. In contrast, the gain of optokinetic reflex in tilted mice was significantly higher in the low-frequency range than in control mice, regardless of the position of the mice in space or the plane of the eye movements. To explain these results, a simple model was used in which a multisensory integration unit was embedded. With this model, we were able to simulate all the behaviors observed. Thus our data and the model support the presence of the multisensory integration system and revealed a compensatory enhanced optokinetic reflex in tilted mice, indicating an adaptive synergism in the processing of otolith and visually driven signals.

Acceleration↗
PubMed1992

Effect of post-training unilateral labyrinthectomy in a spatial orientation task by guinea pigs.

The effects of unilateral labyrinthectomy in guinea pigs have been studied on an angular orientation task consisting, in an open field, of running to a hidden goal oriented at 45 degrees with respect to the cephalocaudal axis of the animal placed in a starting-box. The task was conducted in light but in an homogeneous environment, i.e. without visual, auditory or olfactory cues indicating the location of the goal. A second group of animals was submitted to a similar task running to a hidden goal but the place of the goal was indicated by a colored card. All the animals were trained before the lesion and tested in their respective task for 1 month after the lesion. In the task conducted without conspicuous cues, animals were dramatically disturbed. In contrast, animals pretrained in the visually guided task were not impaired after the lesion. These results point out the important role of vestibular information in performing spatial tasks based on angular estimation, since, even if proprioceptive and visuokinesthetic information remain available, subjects seemed not able to maintain a correct angular trajectory. The trajectories being not disturbed in the visually guided task, one can exclude the hypothesis that such deficit was due to a purely motor disturbance.

Animals↗
PubMed2005

Balance disorders in headache patients: evaluation by computerized static stabilometry.

OBJECTIVES: The aim of the study was to investigate the occurrence of equilibrium disturbances in headache patients, during the interictal period, by computerized static stabilometry. MATERIALS AND METHODS: Sixty-seven patients were studied: 35 with migraine without aura (MwoA), 12 with tension-type headache (TTH) in the episodic form (ETTH) + MwoA, and 20 with only TTH [10 ETTH + 10 chronic (CTTH)]. The stabilometric parameters considered were: statokinesigram length (L) and surface (S) in open (EO) and closed (EC) eyes conditions with/without occlusal bite, EC with head retroflexion (ECR), and optokinetic stimulation (OKN). RESULTS: The alteration of at least one of the stabilometric parameters was observed in 45 patients (67.2%): 21 MwoA, 8 ETTH + MwoA, and 16 TTH (8 ETTH + 8 CTTH). CONCLUSION: In TTH patients (ETTH, CTTH, ETTH + MwoA), the stabilometric findings show a proprioceptive alteration induced by cervicofacial muscle contraction, which was peripheral in origin. In MwoA patients the alterations appear under OKN and support a control impairment in involuntary oculomotility of central origin.

Adult↗
PubMed1995

Control of the head in response to tilt of the body in normal and labyrinthine-defective human subjects.

1. Head movement responses to discrete, unpredictable tilts of the trunk from earth upright were studied in normal and labyrinthine-defective (LD) subjects. Tilts of the seated, restrained trunk, were delivered in pitch and roll about head-centred axes and approximated raised cosine displacements with peak amplitudes of 20-30 deg and durations of 1.5-2 s. Subjects performed mental arithmetic with eyes closed or read earth-fixed text. 2. At the onset of tilt the head momentarily lagged behind the trunk because of inertia. Subsequently, head control varied widely with three broad types: (i) head relatively fixed to the trunk (in normal subjects and some patients); (ii) head unstable, falling in the direction of gimbal tilt (typical of acute patients for pitch motion); (iii) compensatory head movement in the opposite direction to gimbal tilt (observed consistently in normal subjects and in well-adapted patients). 3. EMG was well developed in subjects with compensatory head movement and consisted of an initial burst of activity at minimum latencies of 25-50 ms (means 72-108 ms), followed by a prolonged peak; both occurring in the 'side up' neck muscles, appropriate for righting the head. These muscles are shortened during the initial head lag so the responses cannot be stretch reflexes. In normal subjects their origin is predominantly labyrinthine but in patients they may be an 'unloading response' of the neck. 4. Head stability in space was superior with the visual task for all subjects but vision only partially compensated for labyrinthine signals in unstable patients. 5. Modelling the responses to tilt suggests that, in LD subjects, the short-latency burst could be driven by signals from the neck of the relative acceleration between head and trunk tilt. The longer latency EMG could be driven by a signal of head tilt in space. Normally, this signal is probably otolithic. In patients it could be synthesized from summing proprioceptive signals of position of head on trunk with trunk tilt.

Adaptation, Physiological↗
PubMed1990

A basic posture control mechanism: the stabilization of the centre of gravity.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. The visual, vestibular and muscle proprioceptive systems have all been shown to contribute to sway stabilization. Nevertheless, earlier work has suggested that an additional receptor system is needed to signal the position of the body's centre of gravity relative to the support surface, i.e., the feet. This proposed receptor system should be 'gravity' dependent. To evaluate the properties of this receptor system, an experiment was designed under simulated 'microgravity', in water immersion. An approximately linear relationship was found between contact force and impulse directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. A gain control mechanism for postural reflexes which is dependent on body weight was demonstrated. In a further experiment it could be shown that the receptors for this mechanism are distributed along the vertical axis of the body: it is suggested that these force-dependent receptors are pressure receptors within the joints and the vertebral column.

Adult↗
PubMed1974

Changes in unit postsynaptic responses at sensorimotor cortex with conditioning in rabbits.

A localized, conditioned startle reaction (LCSR) to a click (as conditional stimulus) could be established and recorded electromyographically in rabbits if complex unconditional stimulus was employed. The complex consisted of localized, electrical stimulation applied concurrently to sensorimotor cortex and hypothalamus. The latency of this LCSR was only 12-14 ms. Postsynaptic responses were recorded intracellularly or quasi-intracellularly within the sensorimotor cortex near the placement of the electrodes for the cortical stimulation. The latency distributions of the averaged postsynaptic responses were compared for the naive, conditioned and extinguished dates. Latencies in naive animals were similar to those in the extinguished state, but were significantly (P less than 0.011) different from the Latencies of click-responses in the conditioned state. An increase in the number of responses with 8-17 ms latencies was found after conditioning. Of 30 neurons recorded in conditioned animals six responded with an extremely short latency of 4 to 7 ms. Similar latencies were found in response to much more intense clicks capable of evoking an unconditioned startle reaction in naive animals. Changes in postsynaptic potentials thus occur at the cortex independent of proprioceptive feedback from the conditioned movement. The short latency neuronal responses suggest that a pathway for the LCSR may pass through the sensorimotor cortex. The appearance of responses at less than 7 ms to a previously neutral click in conditioned animals supports the idea that an increase in synaptic effectiveness underlies the neuronal mechanism of conditioning.

Animals↗
PubMed2002

Lid restraint evokes two types of motor adaptation.

Unilateral reduction in eyelid motility produced two modes of blink adaptation in humans. The first adaptive modification affected both eyelids. Stimulation of the supraorbital branch of the trigeminal nerve (SO) ipsilateral to the upper eyelid with reduced motility evoked bilateral, hyperexcitable reflex blinks, whereas contralateral SO stimulation elicited normally excitable blinks bilaterally. The probability of blink oscillations evoked by stimulation of the ipsilateral SO also increased with a reduction in lid motility. The increased probability of blink oscillations correlated with the enhanced trigeminal reflex blink excitability. Thus, the trigeminal complex ipsilateral to the restrained eyelid coordinated an increase in excitability and blink oscillations independent of the eyelid experiencing reduced motility. The second type of modification appeared only in the eyelid experiencing reduced motility. When tested immediately after removing lid restraint, blink amplitude increased in this eyelid relative to the normal eyelid regardless of the stimulated SO. A patient with seventh nerve palsy exhibited the same two patterns of blink adaptation. These results were consistent with two forms of adaptation, presumably because unilateral lid restraint produced two error signals. The corneal irritation caused by reduced blink amplitude generated abnormal corneal inputs. The difference between proprioceptive feedback from the blink and expected blink magnitude signaled an error in blink amplitude. The corneal irritation appeared to drive an adaptive process organized through the trigeminal complex, whereas the proprioceptive error signal drove an adaptive process involving just the motoneurons controlling the restrained eyelid.

Adaptation, Physiological↗
PubMed2005

Changes in muscle activity with increasing running speed.

Electromyographic (EMG) activity of the leg muscles and the ground reaction forces were recorded in 17 elite male middle-distance runners, who performed isometric maximal voluntary contractions (MVC) as well as running at different speeds. Electromyograms were recorded from the gluteus maximus, vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior. The results indicated that the averaged EMG (aEMG) activities of all the muscles studied increased (P < 0.05) with increasing running speed, especially in the pre-contact and braking phases. At higher speeds, the aEMG activities of the gastrocnemius, vastus lateralis, biceps femoris and gluteus maximus exceeded 100% MVC in these same phases. These results suggest that maximal voluntary contractions cannot be used as an indicator of the full activation potential of human skeletal muscle. Furthermore, the present results suggest that increased pre-contact EMG potentiates the functional role of stretch reflexes, which subsequently increases tendomuscular stiffness and enhances force production in the braking and/or propulsive phases in running. Furthermore, a more powerful force production in the optimal direction for increasing running speed effectively requires increased EMG activity of the two-joint muscles (biceps femoris, rectus femoris and gastrocnemius) during the entire running cycle.

Adult↗
PubMed1998

Development of muscle afferents in the spinal cord of the tammar wallaby.

The development of muscle afferents in the tammar wallaby was examined to address whether proprioceptive input contributes to the marked asymmetry of the fore and hindlimb movement. Anatomical tracing with biocytin showed that the muscle afferents had reached the brachial motor horn by postnatal day (P1), but were less advanced in the lumbar region. Labelled cells lying outside the motor horn, presumably filled via gap junctions, were evident in the neonatal lumbar cord. By the 4th postnatal week, the afferent innervation of both brachial and lumbar cords became similar. Afferent discharges from stretching the biceps muscle could be recorded at birth, but not until P4 from the hindlimb gastrocnemius muscle. The discharges were predominantly phasic until P35 when tonic activity could also be recorded. Short latency spinal reflex responses superimposed upon a longer lasting potential were present in the brachial cord at birth, appearing in the lumbar cord at P4. By the 3rd postnatal week, spinal reflex became comparable in both segmental levels. The time course of muscle afferent development was compared to the progression of natural cell death in the lumbar cord. Sensorimotor connections were established towards the end of the rapid phase cell death as observed in other vertebrates.

Action Potentials↗
PubMed2001

Large-fiber neuropathy in distal sensory neuropathy with normal routine nerve conduction.

Near-nerve needle sensory nerve conduction of plantar nerves in 100 patients with distal sensory neuropathy with normal routine nerve conduction (DSN-NNC) found the definite neuropathy pattern (abnormality in more than three of six tested nerves) in 65%, axonal neuropathy in 35%, and the known cause in 37% of patients. Absent or diminished reflexes were a reliable indicator for large fiber neuropathy (LFN). This near-nerve needle plantar nerve study provides useful and unequivocal evidence of its value in identifying neuropathy in DSN-NNC by finding LFN in 65% of patients.

Action Potentials↗
PubMed1994

The influence of a bilateral peripheral vestibular deficit on postural synergies.

The role of vestibular sensory information in the triggering, selection and modulation of postural response synergies was evaluated by comparing the EMG responses of normal subjects to balance perturbations with those of subjects with a bilateral peripheral vestibular deficit. The balance perturbations were a rotation and/or a translation of a support surface on which the test subjects stood with eyes open. Onset latencies and most timing patterns of muscle responses were not altered in vestibular-loss subjects. Major changes were observed, however, in the muscle amplitude synergy. Responses between 120 and 240 ms in tibialis anterior, soleus, and quadriceps muscles were reduced more than 50% with respect to normal amplitudes. In contrast, responses in paraspinal muscles were enhanced nearly 100% with respect to normal values. These changes in muscle amplitudes with accompanying vestibular loss were highest for rotation and lowest for translation perturbations. The identification of a bilateral vestibular loss using EMG amplitudes was always 100% correct for rotation perturbations and between 75 to 85% correct for translation perturbations. Multivariate linear correlations between muscle EMG response areas, and the amplitudes of initial link velocities revealed an increased contribution of afferent signals from the upper leg and a decreased dependence on signals from the trunk and head to postural synergies in vestibular-loss subjects. The afferent modulation of the muscle amplitude synergy correcting a balance disturbance to the stance of normal subjects is, on the basis of these findings, highly dependent on vestibular afferent signals. Our results indicate that vestibular afferent signals are used to enhance the amplitude of responses in tibialis anterior, quadriceps, and soleus muscles; and inhibit the responses of paraspinal muscles, once the response timing has been triggered and selected by proprioceptive signals. Lacking this modulation, bilateral vestibular deficit subjects respond to balance perturbations under eyes-open conditions as if the perturbation were 50% slower. Clinically, our results document that the perturbation of choice, when testing vestibular deficit patients, is a rotation (greater than 3 degrees in amplitude and 15 degrees/s in velocity) and not a translation of the support surface.

Adult↗