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PubMedDate not supplied

The influence of visual and somatosensory input on the vestibulo-oculomotor reflex of pigmented rats.

Eye movements were recorded in the pigmented rat during vestibular, optokinetic and combined visual-vestibular stimulation. The dominant time constant in pigmented rats, tested during angular vestibular stimulation in darkness, is about two times longer than the cupular time constant. The gain and the duration of nystagmus, achieved by angular vestibular stimulation, can be enhanced by visual impulses. This is most evident during an optokinetic temporonasal stimulation, but is also seen with a nasotemporal stimulation. A mere optokinetic monocular stimulation without a synchronous vestibular excitation causes nystagmus only when the stimuli has a temporonasal direction. The duration of nystagmus, achieved by angular vestibular stimulation, is prolonged by disturbances of the neck proprioceptive system. This is more evident during a simultaneous visual input than in darkness. The ability to cancel nystagmus during conflicting vestibular and optokinetic impulses is well developed in the pigmented rat.

Animals↗
PubMed1967

Motor activity following the silent period in human muscle.

1. When a muscle is unloaded during voluntary contraction, there is normally a silent period in the electromyogram. The silence is terminated by a sudden return of muscle action potentials.2. In order to investigate the mechanism of the terminal motor volley, the unloading reflex was studied in six human subjects. The independent variables were the initial muscular force, the inertia of the limb and the amount of motion permitted. The dependent variables were the size and latency of the terminal volley.3. During isometric contraction, the amplitude of the surface-recorded muscle action potentials increased monotonically with increasing muscular tension.4. The action potentials were significantly larger during the terminal volley than during the period before unloading.5. When acceleration of the limb was reduced by increasing the inertia, the terminal volley was decreased in size, but the latency was not affected.6. When movement was interrupted by a mechanical block, the latency of the terminal volley was reduced, but the size was not affected.7. The results suggest that the terminal motor volley is not the result of a decrease in Renshaw feed-back or in autogenetic inhibition.8. The motor volley must be regulated by proprioceptive feed-back, because it is affected by the velocity and displacement of the limb.9. The muscle frequently responded within 20 msec after motion of the limb was blocked. Hence it appears that the mechanism involves a spinal reflex.10. Because the motor discharge occurs while the muscle is shortening, it cannot be an ordinary stretch reflex. If the discharge is attributed to spindle afferent driving, one must assume that the gamma motor neurones are active during the silent period.11. The authors postulate a fusimotor reflex, which is driven by afferent impulses from the moving limb and excites the alpha motoneurones by way of the ;gamma loop'.

Action Potentials↗
PubMed1982

Effects of thoracic dorsal rhizotomy or vagotomy on inspiratory muscle activity at various levels of chemical drive.

The relationship between relative peak activity (moving average EMG) of the diaphragm (Adi) and of the cranial (2nd and 3rd) external intercostal or parasternal muscles (Aic) was assessed during rebreathing in animals before and after bilateral thoracic (T1-T4) dorsal rhizotomy (TDR) and/or bilateral vagotomy (VGT). The relationship had the form Aic=a Adib under all conditions. In intact rabbits and cats mean values for b were 1.48 and 1.79, respectively, a being unity by definition. Neither TDR nor VGT changed b; a decreased to about 0.15 with TDR and halved with VGT only if performed before TDR. Selective reflex facilitation of inspiratory intercostals with occlusions at FRC was observed after VGT and was abolished by TDR. Neither VGT nor TDR affected Adi time course. Hence: (1) central command to alpha-motoneurones of the major inspiratory muscles differs; (2) proprioceptive feedback markedly increases external intercostal activity, apparently by multiplying Aic due to central command to alpha-motoneurones by a factor independent of chemical drive; (3) vagally mediated augmentation of Aic depends entirely on intact proprioceptive feedback. The possible role of fusimotor drive is discussed.

Animals↗
PubMed2005

Strabismus and sensory-motor function of eye muscles.

Paul Bach-y-Rita and coworkers at the Smith-Kettlewell Institute of Visual Science of San Francisco were among the first to record activity in the muscle fibers of the eye muscles in animals. With their newly developed methods, they could describe fast and slow muscle fibers types and present possible patterns of recruitment of the fibers in different eye movements. These studies have been critical for continued animal research on eye muscle fibers and motor units in different species and in animals of different ages. Bach-y-Rita and coworkers also recorded from receptors in the muscles and demonstrated stretch reflexes different from those of skeletal muscles. Further research in animals revealed that it was difficult to delineate the functional role of the muscle receptors in oculomotor control. However, recent studies on sensory functions of human extra ocular muscles have suggested that proprioception participates in space localization, and the functions may differ in normal and strabismic subjects. The eye muscle studies initiated by Bach-y-Rita have enabled analysis of the sensory-motor components of strabismus or squint in greater detail than before.

Animals↗
PubMed1985

Afferent perturbations during "monopodal" swimming movements in the turtle: phase-dependent cutaneous modulation and proprioceptive resetting of the locomotor rhythm.

Locomotion consists of a repeating series of movement cycles (locomotor rhythm) with an orderly activation of musculature during each movement cycle (intracycle motor pattern). The effects of sensory stimulation, on both the intracycle motor pattern and the locomotor rhythm, were examined during electrically elicited swimming movements of a single turtle hindlimb. The resulting "monopodal" swimming was not subject to movement-related reflexes from other limbs or postural constraints, and provided a sensitive system for analyzing the effects of transient sensory perturbations. During "monopodal" swimming, cutaneous and extensor muscle-nerve stimulation (single 0.1- to 0.3-msec electrical pulse) had similar phase-dependent effects on the swim cycle in progress. Stimuli delivered during the powerstroke (limb retracting) shortened the period of the cycle. Stimulation during the returnstroke prolonged the cycle. Changes in cycle period were accompanied by in-phase adjustments of the EMG burst duration or interburst interval which was being expressed at the time of stimulus delivery. The in-phase adjustment of each muscle served to maintain the timing relationships between muscles, and resulted in the preservation of the intracycle motor pattern. Cutaneous and muscle-nerve stimulation had dramatically different effects on the locomotor rhythm. Cutaneous nerve stimulation produced period changes in poststimulus cycles which led to a temporary phase shift of the swimming rhythm. This temporary modulation suggests that cutaneous afferents do not have direct access to the timing circuitry of the central nervous system locomotor network. Muscle-nerve stimulation only altered the period of the cycle in progress at the time of stimulus delivery, and thus permanently reset the locomotor rhythm. This permanent phase shift suggests that muscle afferents have direct access to a central timing network which controls the locomotor rhythm.

Afferent Pathways↗
PubMed1987

The physiology of idiopathic dystonia.

Dystonia is mysterious and its pathophysiology is uncertain. The fundamental motor abnormality is an abnormality of muscle command signals, such that the wrong agonists may be activated for too long, there is abnormal co-contraction of agonist and antagonists, and there is excessive and misdirected action of synergists and postural fixators. The result is action dystonia. In addition, muscle spasms may occur spontaneously. The peripheral motor apparatus, the corticomotoneurone pathway, and (as far as is known) the proprioceptive feedback machinery, are all intact in primary dystonia. However, a defect of interneuronal machinery has been identified in both the brainstem and spinal cord. In blepharospasm there is hyperexcitability of the lower brainstem interneurones responsible for the R2 component of the blink reflex. In the dystonic arm there is loss of the later phases of Ia reciprocal inhibition from extensors to flexors. Both deficits may be due to loss of normal basal ganglia inputs onto interneurones. The known sites of focal lesions that may cause symptomatic dystonia all impair basal ganglia output. However, whether such abnormal interneuronal function is sufficient to explain dystonia is not known. Among many unanswered questions are 1) are the cortical instructions for movement specified correctly, and 2) what is responsible for the spontaneous dystonic spasms?

Dystonia↗
PubMed1992

Hereditary sensory radicular neuropathy: defective neurogenic inflammation.

Hereditary sensory radicular neuropathy exhibits autosomal dominant inheritance with complete penetrance in males and incomplete penetrance in females. Newer tests of small sensory nerve function were used in screening 8 family members aged between 14 and 66 years. All exhibited some frequent features of the disorder with an onset in the 2nd or 3rd decade, foot ulceration, foot callus, loss of pin prick, thermal and light touch sensation, and some reduction in vibration acuity and proprioception in the lower limbs. The hands were involved in 3 of 8, muscle involvement was present in 5 of 8, but deafness was not detected by audiometry. Nerve conduction velocity, sensory action potentials, latency and amplitude, thermal acuity, vibration acuity and axon reflex flares were measured in all patients. One sural nerve biopsy confirmed the presence of peripheral fibre loss in this predominantly sensory neuropathy. Chemically evoked axon reflex tests were used to evaluate the extent of primary sensory nerve fibre involvement. All patients were tested using a Moor MBF 3-D dual channel laser Doppler velocimeter. Acetylcholine or phenylephrine iontophoretically applied as 16 mC doses evoked absent or tiny axon reflexes in areas of impaired pin prick sensation. By contrast, direct microvascular dilator responses to nitroprusside (smooth muscle dependent) and acetylcholine (endothelium-dependent) were present but somewhat reduced in areas with defective neurogenic inflammation. These results differ significantly from the responses obtained in age-matched healthy controls (P < 0.05). Foot pressure analysis was performed for orthoses in 2 affected members with foot ulceration using the Musgrave Footprint system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2002

Neck vibration causes short-latency electromyographic activation of lower leg muscles in postural reactions of the standing human.

To study how quickly cervical proprioceptive information induced muscular responses in the lower leg to control posture in the standing human we investigated lower leg muscle electromyography and force-plate data from 10 healthy normal subjects, when perturbed by posterior neck muscle vibration. At the onset of vibration the tibialis anterior muscle was activated at latencies of 70-100 ms whilst the triceps surae muscle was inhibited at the same latencies. At offset the opposite pattern was observed. These findings suggest that a short-latency integrative system, rather than a direct reflex, mediates the cervical influence on posture. The short latencies also imply that activation of postural muscles in response to vibration towards the neck muscles occurs faster than would be expected if it was caused only by a perceptive illusion of movement.

Adult↗
PubMedDate not supplied

[Rehabilitation in multiple sclerosis: clinico-instrumental correlations].

The Authors report their experience in a patient with Multiple Sclerosis. The planning and the follow up of rehabilitative treatment were based on clinical, functional, electrophysiological and posturographic evaluation. The impairment degree was evaluated by Kurtzke's Expanded Disability Status Scale. The electrophysiological evaluation showed an abnormal recruitment flexor pattern at exteroceptive stimulus and posturography confirmed postural control disorder. The treatment was based on PNF techniques and postural feedback on standing balance platform. After rehabilitative treatment the clinical and functional improvement has been confirmed by normal exteroceptive flexion reflex and better stabilometric parameters.

Electromyography↗
PubMed1995

The role of haptic cues from rough and slippery surfaces in human postural control.

Haptic information is critically important in complex sensory-motor tasks such as manipulating objects. Its comparable importance in spatial orientation is only beginning to be recognized. We have shown that postural sway in humans is significantly reduced by lightly touching a stable surface with a fingertip at contact force levels far below those physically necessary to stabilize the body. To investigate further the functional relationship between contact forces at the hand and postural equilibrium, we had subjects stand in the tandem Romberg stance while being allowed physically supportive (force contact) and non-physically supportive (touch contact) amounts of index fingertip force on surfaces with different frictional characteristics. Mean sway amplitude (MSA) was reduced by over 50% with both touch and force contact of the fingertip, compared to standing without fingertip contact. No differences in MSA were observed when touching rough or slippery surfaces. The amplitude of EMG activity in the peroneal muscles and the timing relationships between fingertip forces, body sway and EMG activity suggested that with touch contact of the finger or with force contact on a slippery surface long-loop "reflexes" involving postural muscles were stabilizing sway. With force contact of the fingertip on a rough surface, MSA reduction was achieved primarily through physical support of the body. This pattern of results indicates that light touch contact cues from the fingertip in conjunction with proprioceptive signals about arm configuration are providing information about body sway that can be used to reduce MSA through postural muscle activation.

Adult↗
PubMed1985

Peripheral influences on the central pattern-rhythm generator for tongue movements in the rat.

Rhythmic activity in the tongue and other oral muscles was evoked by mechanical stimulation of the hard palate in ketamine-anaesthetized rats. The relation between neural discharges of single hypoglossal motoneurones and activity in the masseter and anterior digastric muscle, and stimulus parameters was analysed. By varying the stimulus parameters, hypoglossal-motoneurone activity was modulated from phasic reflex activity into rhythmic activity. The tongue and other recorded muscles are likely to be controlled by the same pattern-rhythm generator, when rhythmic activity is induced by palatal stimulation. Exteroceptive oral stimuli can activate the tongue pattern-rhythm generator independently of proprioceptive feedback. Proprioceptive input from oral structures influenced the burst duration of rhythmic hypoglossal motoneurone activity. The cycle duration and the number of discharges/burst, however, was not affected by proprioceptive input. The hypoglossal-motoneurone pool may be influenced by more than one pattern-rhythm generator because the burst characteristics of rhythmically-firing hypoglossal motoneurones depend upon stimulus conditions. These hypoglossal pattern-rhythm generators have possible hierarchic relations because a shift from one burst pattern into another can be evoked by changing stimulus conditions. The pattern-rhythm generators for oral movements may be composed of a neural-pattern generator and a neural-rhythm generator, which can be modulated separately by peripheral inputs.

Action Potentials↗
PubMed1987

[Neuropathy caused by cisplatin. 7 cases including one with an autopsy study].

The clinical, electrophysiological and histopathological features in seven cases of cisplatinum peripheral neuropathy are reported and compared with the literature data. The neuropathy appears for an average intake of 500 mg/m2 of DDP. The symptoms are those of a symmetric, distal, predominantly sensitive neuropathy of an axonal type with major involvement of proprioception. Neurological improvement is poor after withdrawal of the drug. A post mortem study performed in one case showed a degeneration of the posterior column in the cord and residual nodules of Nageotte in a lumbar spinal ganglion. The systematic study of the tendon reflexes and distal pallesthesia in subjects treated with the drug, may reveal the neuropathy before the onset of the most disabling symptoms (paresthesia, ataxia, pain, Lhermitte's sign).

Adult↗
PubMed1992

Characteristics of dynamic postural reactions in the locust hindleg.

The use of the locust (Schistocerca americana) hindleg in postural control was examined in animals that stood on a repeatedly swayed vertical substrate. Myograms were recorded from leg muscles and the angle of the femoro-tibial joint was monitored photographically. Two discrete strategies were observed; in compensatory reactions the hindleg was held in place, while in "flexion" reactions, the leg was moved, most often to complete flexion of the femoro-tibial joint. Tightly coupled, rhythmic bursting occurred in the flexor and levator muscles of the leg during compensatory reactions. Bursting was initiated repeatedly when the substrate was being pulled away from the animal. Bursting was correlated with subsequent decreases in the rate of change of the femoro-tibial joint angle. Compensatory and "flexion" reactions occurred preferentially in different ranges of joint angles: most often, compensatory reactions occurred in the mid-range, while "flexion" reactions were elicited in the extremes of joint angle. These differences may be due to the mechanical advantages of the tibial muscles and the leg may be moved to full flexion because of a locking mechanism of the flexor muscle tendon. These reactions are compared with known reflexes of hindleg proprioceptors and contrasted with similar responses of vertebrates.

Animals↗
PubMed1994

Sensory interaction posturography in patients with peripheral vestibular disorders.

The results of posturography, using all sensory inputs, are compared with recordings when one or more of the sensory inputs are altered by the test conditions. This gives an idea of the sensory interaction in central compensation in the vestibulospinal reflex. Positive and negative effects could be observed in patients with peripheral vestibular disorders.

Female↗
PubMed1990

Normal proprioceptive trigeminal afferents in patients with Sjögren's syndrome and sensory neuronopathy.

A pure sensory neuropathy due to neuronal damage in the gasserian and spinal ganglia has been described in patients with Sjögren's syndrome. Conventional electromyographic (EMG) studies can demonstrate the selective involvement of the sensory pathways but they do not provide definite evidence for the site of the lesion. Noting that the trigeminal sensory neurons carrying cutaneous and muscular afferents are differentially located in the gasserian and mesencephalic nuclei, respectively, we carried out an electrophysiological study of the trigeminofacial and trigeminotrigeminal reflexes in 5 patients with Sjögren's syndrome and pure sensory neuropathy, in 10 patients with sensory-motor neuropathies of other causes, and in 10 healthy subjects. Our results show that patients with Sjögren's syndrome and pure sensory neuropathy who exhibited abnormal blink reflexes and an abnormal, cutaneous-induced masseter silent period had normal jaw jerks, whereas patients with sensory-motor neuropathies who exhibited abnormal cutaneous responses had abnormal jaw jerks. These findings suggest that the lesion in pure sensory neuropathy involves damage to the neurons of the gasserian ganglia and not to the trigeminal axons, since an axonal lesion would be expected to involve the large axons from muscle spindle receptors.

Adult↗
PubMed1988

Reflex modulation of phrenic activity through hindlimb passive motion in decorticate and spinal rabbit preparation.

The neurogenic effect of passive hindlimb movement on phrenic nerve discharge was compared in decorticate unanaesthetized and curarized rabbit preparations prior to and after spinal transection. The question of how and where sensory information has access to the central respiratory network was addressed in each case. All passive motions, performed using a mechanical device, were of constant amplitude in a given preparation. The results clearly differed in decorticate and spinal preparations. In the decorticate vagotomized preparation, periodic passive motions led to an immediate shortening of the respiratory period which lasted throughout the periodic stimulation and stopped with its cessation; it did not depend on the frequency of the natural stimulation and was entirely due to a 20% shortening of the expiration time. Maintained full flexion or full extension both induced the same expiration time shortening, but limited to the first two to three respiratory cycles after onset and interruption of stimulation. After spinal transection at the C2 level, and moderate activation with DOPA, no phrenic activity developed in the absence of proprioceptive stimulation. Periodic hindlimb movements evoked simultaneous large bursts in both phrenic nerves during each extension; a 1:1 coordination of phrenic activity with the external imposed period (P) was observed for various P values. A strong phrenic activation could also be elicited through maintained full hindlimb extension but not through full flexion: this activation appeared as rhythmic discharge as long as extension was maintained. It is concluded that proprioceptive inputs act upon the medullary respiration generator and reset its own rhythm whereas, at the spinal level, they elicit an amplitude modulation at phrenic motoneuronal level without acting upon the rate of the spinal "respiration" generator itself; on the same phrenic motoneurons, a subthreshold central activation added to a subthreshold proprioceptive activation probably accounts for the phrenic bursting during maintained extension. Finally, the proprioceptive control from the hindlimb on phrenic activity is processed at different sites of the central respiratory network at medullary and at spinal level, and may depend on different input signals.

Animals↗
PubMed1992

Visually controlled spatial stabilisation of the human head: compensation for the eye's limited ability to roll.

During movements of the head in pitch (yes-yes) or in yaw (no-no) the visual scene appears stable whereas rolling the head (ear down to shoulder) induces an apparent swinging of the world in the opposite direction. This visual instability is due to the inadequacy, in the roll plane, of the reflex eye movements which are effective in stabilising the eyes in space during pitch and yaw. We investigated whether head is stabilised in roll to protect against visual instability. Human subjects were fixed in a gimbal with their heads free and were exposed to unpredictable oscillatory movement in pitch and, for comparison roll, about axes aligned with the head. With vision, during roll motion, the head was displaced from upright by approximately half the amplitude of the gimbal motion. In comparison, with eyes closed relying on vestibular and proprioceptive cues and during pitch stimuli with or without vision, the magnitude of head displacement from upright was approximately equal to that to the gimbal. The superior head stability in roll, dependent on a visual frame of reference, compensates for poverty of eye movement in this plane.

Eye Movements↗