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Biomedical subjects

G M Gauthier

Publications and source records attributed to G M Gauthier.

At least 55 records · Page 3Linked to original sources
PubMed1986

Inhibitory effects of combined agonist and antagonist muscle vibration on H-reflex in man.

Vibration alters human sensory motor performance. Changes in the excitability of spinal reflex mechanisms may be responsible for the majority of the observed alterations. We studied the differential effects of vibration locally applied to gastrocnemius soleus and tibialis anterior muscles separately and to both muscles simultaneously. From the results, it is deduced that combined agonist and antagonist muscle vibration may lead to summative interaction between pre- and postsynaptic inhibition at motoneuronal level. Whole-body vibration is taken to mean a combination of synchronous vibrations applied locally and simultaneously to several muscles. The results also demonstrate that the level of inhibition of the H-reflex resulting from the vibration is directly related to the displacement amplitude of the vibration, regardless of the frequency.

Adolescent↗
PubMed1986

Comparative effects of whole-body vibration on sensorimotor performance achieved with a mini-stick and a macro-stick in force and position control modes.

The aim of this investigation was to assess the performance of subjects in a target recentering task, performed under both normal and vibration conditions. A conventional helicopter stick and an arm-side controller were used in both position and force control modes. The task was designed to simulate instrument flying. The results showed that in the no-vibration situation, the highest performance was achieved in the force control mode and little difference was observed between the two sticks. They also showed that vibration impaired the velocity control of the performance. It is suggested that the subject might be switching over from a visual and arm afferent and efferent control in the no-vibration situation, to a visual control only under vibration condition. From this study, it appears that the more efficient stick to execute the designed task is the mini-stick operating in the force control mode.

Adult↗
PubMed1986

Adapted head- and eye-movement responses to added-head inertia.

Adaptation to inertia added to the head was studied in man by mounting masses on a rigidly attached helmet. Two- to ten-fold increases of inertia were thus produced, while an overhead suspension compensated for the weights. Eye and head positions and corresponding velocities were simultaneously recorded during eye-head tracking of a target stepping at 0.2 Hz in the horizontal direction. Without added inertia, fast gaze movements are type III, the accelerated head movement coming early and the resulting VOR truncating the simultaneous eye movement saccade in both amplitude and velocity. Head oscillations are fast and overcompensated by higher gain VOR. With added inertia, the adapted head movement is slowed and delayed. This permits the eye movement saccade to be completed before head movement begins and to escape truncation; the saccade is normal or slightly increased in amplitude. Head oscillations are slow and compensated by normal gain VOR. Either truncation of the saccade or overcompensation of the VOR leads to eye movement and gaze position error that is corrected for by secondary corrective saccades. These same two errors in gaze coordination could explain the cause of the perceived oscillopsia. Oscillopsia, or continual displacement or instability of the visual worlds, is a symptom of breakdown of space constancy, and was prominent and consistent in perceptual reports of our subjects. Adaptation resulting from adding inertia to the head occurred much faster than that induced by adding prisms or lenses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1985

Visually and acoustically augmented performance feedback as an aid in motor control learning: a study of selected components of the rowing action.

The present work compares the efficiency of two training techniques as aids to learning selected aspects of a sequentially ordered action such as that of rowing. Subjects in one group were trained with a conventional learning technique (CLT) while those in a second group were trained by an augmented feedback technique referred to as external feedback (EFB). Progress was recorded on learning curves. Rowing athletes with limited experience and psychophysiology students were used for the study. The tasks consisted of learning movement timing (rhythmicity of action and coordination of body parts) and movement intensity (force and electromyogram development), in four separate experiments. The learning curves for EFB subjects were found to have significantly and consistently higher slopes than those for CLT subjects. Optimal criteria were reached by EBF subjects, after a continuous increase in performance levels and a concomitant decrease in standard deviations evaluated from periodicity, movement accuracy and force. Subjects, who after 8 to 10 sessions of CLT learning had not reached optimal level, were exposed to EFB. Their performances then showed a marked improvement and attained the required criterion in 2 to 4 sessions. This further demonstrates the efficacy of EFB as compared with CLT, as an aid to learning a complex sensorimotor action. The efficacy of EFB as a learning technique is discussed in relation to the internal model of the task to be executed and to sensory motor control and motor programmes.

Adult↗
PubMed1984

Origin of eye movements induced by high frequency rotation of the head.

Perception of stability of the visual world and control of ocular fixation and tracking are altered in subjects submitted to high frequency vibration. Studies of the eye movements induced in man by passively rotating the head sinusoidally around a vertical axis show that beyond 8 Hz, the amplitude of the eye movements increases and reaches 2.5 times the amplitude of head movement at 30 hz. The high amplitude eye oscillation may, at least in part, explain the perception of visual world instability and the decrease of visuo-oculomotor system performance in man submitted to high frequency vibration. Two interpretations of this phenomenon have been proposed (9). High amplitude eye movements induced at high frequency may be due to either a non-linearity of the vestibulo-ocular reflex (VOR) or mechanical resonance oscillations of the orbital apparatus. To test these hypotheses, baboons were trained to fixate visual targets. Each animal's head was rigidly attached to a rotating frame through a block of dental cement bolted to the skull. Head rotation was produced by a servo-controlled vibrator. Rotations in the frequency range 1 to 20 Hz were successively applied with the animal in darkness or fixating a stationary target. The results showed that gain curves obtained with baboons are similar to those obtained with man. Paralysis of the muscles of one eye by injection of lidocaine disclosed a behavioral asymmetry of the two eyes at low frequency. The paralysed eye showed no movement below 8 Hz, while the normal eye behaved as in the normal situation. Beyond 8 Hz, the gain of the treated eye increased gradually so that beyond 12 Hz, the two eyes responded.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

[Experimental design for the study of adaptive properties of the visuo-manual system in subjects newly provided with optic corrections].

Optical corrections may produce, during the first days of wearing, behavioral and psychophysiological changes such as a sensation of illusory motion of the visual world upon head rotation and errors in the manipulation of objects under visual guidance. After a few days, adaptation takes place, leading to the recovery of adequate sensory-motor performance. We describe an experimental system designed to study the adaptation of the visuo-manual system after exposure to optical corrections. The systems consists of a data tablet/digitizer and a micro computer. The quantification of the adaptation is based on the comparison of the average performance of a subject in a visuo-manual pointing task before and after a practice period consisting of pointing at visual targets through the optical corrections. Preliminary results from tests executed with normal subjects show that the system is perfectly suitable to determine the ability of an individual to adapt to optical corrections. This system can be used to systematically study the adaptation phenomena resulting from the alteration of the normal visuo-manual relationship by optical systems.

Adaptation, Ocular↗
PubMed1984

Spinal reflex alterations as a function of intensity and frequency of vibration applied to the feet of seated subjects.

Sensorimotor system performance is known to be altered by vibration applied locally to tendons and muscles or to the whole body. The present study is an attempt to determine the influence of vibration amplitude, acceleration, and frequency on the excitability of the motoneurons as evaluated by the amplitude of electrically induced spinal reflex response in man. The results show that a vibration applied to the legs of a seated subject (S) decreased the reflex response. The effect is directly related to the vibration intensity. The reflex amplitude is minimal in the 10-30 Hz range. At constant acceleration, the depressive effect decreased beyond 20-30 Hz while, at constant displacement amplitude, the reflex inhibition was almost constant throughout the frequency range of 20-60 Hz. These observations suggest that the diminution of the reflex response is mainly related to the amplitude of the vibration, regardless of the frequency. The results are interpreted in light of current knowledge of the effect of locally applied vibration on muscle tendons. The marked inhibition observed in the 10-30 Hz range, even with moderate intensity, suggests that particular attention should be devoted to avoid vibration in that frequency range in vehicles in order to prevent alteration of the performance of sensorimotor systems.

Adolescent↗
PubMed1983

Visual motor rehabilitation in children with cerebral palsy.

Cerebral palsied (CP) children were given intensive visuo-oculomotor training in order to improve their visuo-oculomotor control, using children's films as a visual stimulus. A comparative study was conducted on a group of normal children of the same age. Results showed that training does improve visuo-oculomotor system control as illustrated by (1) a marked increase in smooth pursuit precision and maximum velocity, (2) an improvement of saccadic movement precision and stability, and (3) a shortening of the saccadic reaction time. The highest performance was observed under conditions in which the child pointed at and followed the visuo-acoustic target with his arm extended.

Adolescent↗
PubMed1983

[Development and training of monocular motor control].

Misalignment of the visual axes of the eyes observed in strabismus may result from sensory, motor, and/or central nervous system disorders. The functional properties of a technique designed to increase, through training, the monocular motor control of normal human subjects was evaluated, the ultimate goal being obviously to apply the technique to cases of minor strabismus. The subject is seated in front of a television screen. A diaphragm extending from the subject's head to the screen divides the picture into two visually separated half fields. A micro-computer was programmed to project two patterns on the screen, made up of vertical green and grey bars (spatial frequency, 3 deg.). Displacement of the two visually superposable half fields could be independently achieved. The subject's task was to fixate, with one eye, the corresponding half field maintained stationary and track, with the other eye, the motion of the second half field. Perfect fusion of the two half fields has to be preserved during movements of the mobile half field over 2 to 6 degrees at a frequency of 0.4 Hz. The results show that after a few training sessions, subjects developed a high gain monocular motor control. This observation suggests that the method may be used as therapy to correct minor strabismus with or without anomalous retinal correspondence, and offers the possibility to study static and dynamic characteristics of Panum's areas and particularly their modifications as a function of training of monocular motor control.

Adolescent↗
PubMed1983

Cerebellar control of eye movements studied with injection of harmaline in the trained baboon.

1. The alteration of the cortical cerebellar mechanisms resulting from the activation of the olivo-cerebellar pathway by Harmaline (H) administered at doses which were subthreshold for skeletomotor tremor (5 mg/kg, IM) yields, in the trained Baboon (Papio papio), a marked decrease of oculomotor system performance. 2. The mean angular excursion of the spontaneous eye movements produced in the dark over a given period of time is increased by 50%. The increase is basically due to an increase of the number of saccades in the 0-20 degrees amplitude range. 3. The eye movements in response to a slow target displacement are altered as evidenced by a decrease of the smooth pursuit gain, a 60% increase in latency, and by intrusive saccades. The effects are dose dependent so that around 8 mg/kg of H, smooth pursuit is totally suppressed. 4. The saccadic system is also altered, Stepping target tracking shows dysmetria and increase of the amplitude of the fixation eye movements. The velocity-amplitude relationship of the saccades is not modified but the saccadic reaction time is increased by 50%. The observed alterations are in no way similar to the tremor commonly induced by the drug, at skeletal level. In fact, no ocular tremor at 8 to 10 Hz was recorded. 5. In conclusion, administration of H alters considerably the control and the stability of the oculomotor system in a way similar to that resulting from partial or total cerebellectomy. It may thus be possible to use the drug to simulate, in a reversible manner, cerebellar dysfunctions and study the involvement of the cerebellum in oculomotor control.

Alkaloids↗
PubMed1981

Effects of whole-body vibrations on sensory motor system performance in man.

The effects of whole body vibration (WBV) were studied on subjects trained to perform on tasks involving blindfolded arm positioning (proprioceptive tasks), tracking of visual targets and control of static and dynamic torques. Subjects were vibrated in a seated position by means of a hydraulic jack. The vibration used (0.1 G at floor level and 18 Hz) was that occasionally encountered on medium-size cruising helicopter. The seat was that of a heliccopter pilot whose foam cushion was 6 cm thick with a density of 26 kg/m3. Systematic past-pointing was observed for both arm flexion and extension. Foot and arm visual tracking precision, as determined by position and velocity errors, increased in both directions. Static and dynamic control, rated by torque holding stability and torque amplitude precision, were also significantly altered compared to pre-stimulus readings. The results are interpreted in relation to current knowledge of the effects of vibration induced at spinal, vestibular, and central nervous system levels. It is concluded that the proprioceptive system through which vibration-induced afferents enter the neurological networks is the common denominator for the observed alterations of the position, velocity, and force controls. Our observations suggest that particular care should be taken in helicopters and other vibrating vehicles to prevent vibration from reaching muscular masses, especially those involved in motor tasks.

Adolescent↗
PubMed1980

Effects of whole-body vibration on spinal reflexes in man.

Recent studies have described sensory-motor function alterations resulting from vibrations applied to various parts of the body. The present work describes the effects produced at the myotatic loop level by long-term vibration. Hoffmann and Tendon reflexes as well as tendon vibration response were substantially depressed by 18 Hz, +/- 0.25 G vibration applied to the whole body or to the legs of seated human subjects. The reflex inhibition lasted throughout the 15-min vibration period and persisted minutes after stimulus cessation. In contrast, vibration limited to the S's head and trunk showed much weaker effects. This suggests that the vibration acts mainly upon extero- and proprioceptive receptors rather than upon the vestibular organs. The results are discussed in relation to findings derived from experiments involving locally applied short-duration vibration.

Adolescent↗
PubMed1979

Visual-motor adaptation. Quantitative demonstration in patients with posterior fossa involvement.

Short-term visual-motor adaptation to magnifying spectacle lenses was studied in normal subjects and in patients with nonacute posterior fossa lesions. When normal subjects, looking through magnifying lenses, pointed open loop to targets without viewing their hands, they initially underestimated the distance (magnification effect). After a 20-minute close-loop training or adaptation exposure period during which they viewed the performance of their hands, a modified visual-motor scheme evolved, compensating for about half of the lens-induced pointing error (adaptation effect). Removal of the lenses after adaptation caused open-loop, overshooting pointing errors (adaptation after-effect). Four patients with remission of cerebellar signs showed normal visual-motor adaptive performance, evidence of ability to recalibrate gain. One patient with persisting cerebellar ataxia was unable to recalibrate gain during close-loop visual-motor training. His history of transient palatal myoclonus implicates a role for the cerebellar-olivary system in calibration of visual-motor gain.

Adaptation, Ocular↗