Biomedical subjects

G M Gauthier

Publications and source records attributed to G M Gauthier.

At least 37 records · Page 2Linked to original sources

PubMed1995

Evaluation of saccadic eye movements as an objective test of recovery from anaesthesia.

Saccadic eye movements have been previously used to assess residual effect of anaesthetics, but this test is seldom compared to other psychomotor tests. The aim of the present study was to validate saccades as a recovery index in relation to frequently referred subjective and psychometric tests. Eight healthy subjects were tested before and after intra-muscular injection of either placebo or 0.15 mg.kg-1 of midazolam. Each session consisted of a saccadic test (recorded by electro-oculography), a choice-reaction-time test (CRT), a subjective state-of-alertness test (11 visual analogic scales) and blood sampling (to monitor midazolam plasma concentration), before and 30 (t30), 60 (t60), 120 (t120), 180 (t180), 240 (t240) minutes after drug administration. In the placebo group, there was no change in subjective assessment, saccade characteristics (latency, peak velocity and duration) or CRT results. In the midazolam group, 6 subjective items changed with different time-courses, when compared to baseline: from t30 to t120 (drowsy, in shape, tired, clumsy, strong) and t120 (woolly). Saccade latency and duration were significantly different from t30 to t120 and until t180 for peak velocity. CRT performance was significantly altered from t30 to t120. Midazolam plasma concentration decreased from 177 +/- 33 ng.ml-1 at t30 to 47 +/- 12 ng.ml-1 at t240. At this latter time, sensorimotor functions returned to the baseline. All subjects fulfilled the clinical conditions for home discharge 4 hours after administration. These results suggest that a saccadic eye movement test is a sensitive and reliable tool for the assessment of residual effect of anaesthetics. This test was found to be more sensitive than CRT test since peak saccadic velocity was the last psychometric parameter to be returned to baseline after midazolam injection. This study also confirms the poor reliability of subjective assessment, as subjects tended to underestimate the alteration of their performance immediately following drug injection.

Adult↗

PubMed1995

Perception of passive whole-body rotations in the absence of neck and body proprioception.

1. This study investigated whether accurate perception of body rotation after passive horizontal whole-body rotations in the dark requires the integration of both vestibular and neck-body proprioceptive signals. 2. In the first experiment, the gain of the vestibuloocular reflex (VOR) of normal subjects ("controls") and of a patient without proprioception of the neck and body muscles was assessed by the use of pulse and sinusoidal stimulation. In the second experiment, the subjects reported verbally the magnitude of the body rotations. Finally, in the third experiment, they shifted gaze to the position fixated before the rotation ("vestibular memory-contingent saccades" paradigm). 3. The VOR gain of the patient was similar to that of controls, although the body rotations of the patient were largely overestimated, regardless of whether the patient reported the perceived magnitude verbally or through a gaze shift toward the position gazed at before the rotation. 4. These results suggest that neck muscle proprioception contributes to the vestibular signal calibration at the perceptual level necessary for determining body orientation accurately after rotations in the dark.

Afferent Pathways↗

PubMed1994

Eye-head-hand coordination in pointing at visual targets: spatial and temporal analysis.

This study investigated whether the execution of an accurate pointing response depends on a prior saccade orientation towards the target, independent of the vision of the limb. A comparison was made between the accuracy of sequential responses (in which the starting position of the hand is known and the eye centred on the target prior to the onset of the hand pointing movement) and synergetic responses (where both hand and gaze motions are simultaneously initiated on the basis of unique peripheral retinal information). The experiments were conducted in visual closed-loop (hand visible during the pointing movement) and in visual open-loop conditions (vision of hand interrupted as the hand started to move). The latter condition eliminated the possibility of a direct visual evaluation of the error between hand and target during pointing. Three main observations were derived from the present work: (a) the timing of coordinated eye-head-hand pointing at visual targets can be modified, depending on the executed task, without a deterioration in the accuracy of hand pointing; (b) mechanical constraints or instructions such as preventing eye, head or trunk motion, which limit the redundancy of degrees of freedom, lead to a decrease in accuracy; (c) the synergetic movement of eye, head and hand for pointing at a visible target is not trivially the superposition of eye and head shifts added to hand pointing. Indeed, the strategy of such a coordinated action can modify the kinematics of the head in order to make the movements of both head and hand terminate at approximately the same time. The main conclusion is that eye-head coordination is carried out optimally by a parallel processing in which both gaze and hand motor responses are initiated on the basis of a poorly defined retinal signal. The accuracy in hand pointing is not conditioned by head movement per se and does not depend on the relative timing of eye, head and hand movements (synergetic vs sequential responses). However, a decrease in the accuracy of hand pointing was observed in the synergetic condition, when target fixation was not stabilised before the target was extinguished. This suggests that when the orienting saccade reaches the target before hand movement onset, visual updating of the hand motor control signal may occur. A rapid processing of this final input allows a sharper redefinition of the hand landing point.

Adult↗

PubMed1994

Changes in ocular alignment and pointing accuracy after sustained passive rotation of one eye.

We have investigated the contribution of ocular muscle proprioception (OMP) to the long-term maintenance of ocular alignment in normal human beings. Using a scleral suction lens, one eye was rotated laterally 30 deg away from the position of the other eye. This procedure selectively affects OMP without altering the efferent copy of the ocular motor command. The passively displaced eye was covered while the unimpeded eye fixed upon a stationary target. The suction lens was removed after 6 or 10 min and the measures of alignment begun immediately. Three tests were used to determine the effects of the deviation on ocular alignment: the Lancaster red-green test; saccadic eye movement responses to stepping targets; and hand pointing to monocularly presented targets. All three tests indicated a change of ocular alignment of about 2-4 deg, lasting 5-10 min: sustained temporal deviation resulted in exophoria (relative divergence of the visual axis), and sustained nasal deviation induced esophoria (relative convergence). Binocular viewing rapidly abolished the effect. The hand pointing test showed a large shift in the perceived position of a target during monocular viewing with either eye and its amplitude was correlated with the change of ocular alignment. These results indicate that a sustained passive rotation of one eye can lead to a persistent change in ocular alignment even after the eye is released, without any disparity cues. We further suggest that central mechanisms, based upon ocular motor afferents, rather than passive orbital mechanical factors, are the main cause of this phenomenon.

Adult↗

PubMed1994

[Development of the AC/A ratio following surgery of accommodative esotropia].

Whether surgery should be used to correct for accommodative esotropia is still largely debated among strabologists. Fincham's theory (Fincham and Walton, 1957), describing the interaction between accommodation and vergence control systems (accommodative vergence and vergence accommodation), has been extensively studied. Models suggest that weakening of the accommodative vergence should correct esotropia. To test the model proposed by Semmlow (1981), we compared AC/A ratios in esotropic children and age-related normals (orthophoric) and monitored AC/A ratios for immediate (first week) and long term (1-2 months) changes in esotropic children following surgical correction. The AC/A ratio was determined at near and far. The accommodation stimulus was modified using lenses. The slope of the regression line between accommodation stimulus and disparity provided a measurement of AC/A ratio. Preliminary results show a normalisation of AC/A ratio occurring during the first month after surgery, supporting Semmlow's model and validating surgery as a means to correct for accommodative esotropia.

Accommodation, Ocular↗

PubMed1994

The interactive processes of accommodation and vergence.

A near target generates two different, though related stimuli: image disparity and image blur. Fixation of that near target evokes three motor responses: the so-called oculomotor "near triad". It has long been known that both disparity and blur stimuli are each capable of independently generating all three responses, and a recent theory of near triad control (the Dual Interactive Theory) describes how these stimulus components normally work together in the aid of near vision. However, this theory also indicates that when the system becomes unbalanced, as in high AC/A ratios of some accommodative esotropes, the two components will become antagonistic. In this situation, the interaction between the blur and disparity driven components exaggerates the imbalance created in the vergence motor output. Conversely, there is enhanced restoration when the AC/A ratio is effectively reduced surgically.

Accommodation, Ocular↗

PubMed1993

Dynamic analysis of human visuo-oculo-manual coordination control in target tracking tasks.

Human subjects tracked a visual target controlled either by a function generator (sine wave at different frequencies) or directly by the observer's arm. Gain and phase curves of the oculomotor response as a function of target frequency were determined. Data show that the upper frequency limit of smooth pursuit is higher when the target is driven by the observer's hand, confirming previous reports that smooth pursuit can reach higher velocities when tracking self-moved targets. Comparative analysis of ocular tracking with and without manual target control showed that subjects could be classified into two groups. One group exhibited an increase in gain at high frequency, but showed no significant phase changes. Conversely, the reverse was found in the other group: a significant decrease of phase lag at high frequency and no change in gain. These results demonstrate the existence, within the oculo-manual coordination control system, of at least two separate mechanisms (or strategies), tending either to synchronize the eye and arm motor activities (timing coordination) or to adjust their gain (spatial coordination).

Adult↗

PubMed1992

Oculo-manual coordination control: ocular and manual tracking of visual targets with delayed visual feedback of the hand motion.

The aim of this study was to examine coordination control in eye and hand tracking of visual targets. We studied eye tracking of a self-moved target, and simultaneous eye and hand tracking of an external visual target moving horizontally on a screen. Predictive features of eye-hand coordination control were studied by introducing a delay (0 to 450 ms) between the Subject's (S's) hand motion and the motion of the hand-driven target on the screen. In self-moved target tracking with artificial delay, the eyes started to move in response to arm movement while the visual target was still motionless, that is before any retinal slip had been produced. The signal likely to trigger smooth pursuit in that condition must be derived from non-visual information. Candidates are efference copy and afferent signals from arm motion. When tracking an external target with the eyes and the hand, in a condition where a delay was introduced in the visual feedback loop of the hand, the Ss anticipated with the arm the movement of the target in order to compensate the delay. After a short tracking period, Ss were able to track with a low lag, or eventually to create a lead between the hand and the target. This was observed if the delay was less than 250-300 ms. For larger delays, the hand lagged the target by 250-300 ms. Ss did not completely compensate the delay and did not, on the average, correct for sudden changes in movement of the target (at the direction reversal of the trajectory). Conversely, in the whole range of studied delays (0-450 ms), the eyes were always in phase with the visual target (except during the first part of the first cycle of the movement, as seen previously). These findings are discussed in relation to a scheme in which both predictive (dynamic nature of the motion) and coordination (eye and hand movement system interactive signals) controls are included.

Adult↗

PubMed1990

The role of ocular muscle proprioception in visual localization of targets.

The role of ocular muscle proprioception in the localization of visual targets has been investigated in normal humans by deviating one eye to create an experimental strabismus. The passively deviated eye was covered and the other eye viewed the target. With a hand-pointing task, targets were systematically mislocalized in the direction of the deviated nonviewing eye. A 4- to 6-degree error resulted when the nonviewing eye was offset 30 degrees from straight ahead. When the eye was deviated, the perceived "straight-ahead" was also displaced, by a similar amount, in the same direction. Since the efferent motor commands to the displaced and to the nondisplaced eyes are presumably identical by the law of equal innervation, the mislocalization of visual objects must be attributed to the change in proprioceptive information issued from the nonviewing, deviated eye. Thus proprioception contributes to the localization of objects in space.

Humans↗

PubMed1990

Visual vestibular interaction: vestibulo-ocular reflex suppression with head-fixed target fixation.

In order to maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counterrotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the opto-kinetic reflex. We have studied how, in humans, the VOR gain (VORG) is modulated to provide appropriate eye movements in two situations: 1. fixation of a stationary object of the visual space while the head moves. This requires a visuo-vestibulo-ocular reaction to induce eye movements opposite in direction, and equal in velocity to head movements, and 2. fixation of an object moving with the head. Here, the visuo-vestibulo-ocular reaction should be totally suppressed. These two situations were compared to a basic condition in which, to induce "pure" VOR, the subjects (Ss) in darkness were not allowed a visual target. Eye movements were recorded in seated Ss during constant amplitude sinusoidal and pulse-like passive rotations applied around the vertical axis. Subjects were in total darkness (DARK condition) and performing mental arithmetic. Alternatively, they were provided with a small target, either stationary with respect to earth (earth-fixed target: EFT), or moving with them (chair-fixed-target: CFT). The sinusoidal rotation experiment was used as baseline for the ensuing experiments and yielded control data in agreement with the literature. In particular, rotation in the dark showed a VORG of 0.6. With, for example, 0.8 s passive pulse rotations, typical responses in all three visual conditions were rigorously identical during the first 150 to 180 ms. They showed a delay of about 16 ms of the eye behind the head with no significant difference between passive whole-body and passive head-alone rotations. In all conditions, once the eyes had started to move, a rapid increase in eye velocity was observed during 75 to 80 ms, after which, the average VORG was 0.9 +/- 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 180 ms, the VORG remained around 0.9 in DARK, increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of these later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit. Sinusoidal rotations, extensively used in VOR studies, do not seem to be a satisfactory stimulus to rapidly and precisely characterize VOR function, particularly in pathological cases. Our data suggest that rapid transient rotations are more appropriate.

Adult↗

PubMed1990

Pyridostigmine-induced inhibition of blood acetylcholinesterase (AChE) and resulting effects on manual ocular tracking performance in the trained baboon.

A method was developed to determine the effects of pyridostigmine on sensory-motor control in baboons trained to perform visuo-oculo-manual tracking tasks. The performance was evaluated in terms of accuracy, maximum smooth pursuit velocity, and gain. Administration of pyridostigmine (0.4-0.7 mg/kg intramuscularly) induced a dose-related decrease in smooth pursuit performance which appeared 10 to 30 min after injection and lasted about 1 h. If the animal was allowed to track the target with its hand or to move the target itself, the smooth pursuit performance increased significantly, returning to near normal values. The movement of the hand was not altered. The effect of intramuscular injections of pyridostigmine (0.5 mg/kg) was studied on blood acetylcholinesterase activity in alert baboons. Maximum inhibition of about 60% of baseline activity was observed 10 min after pyridostigmine injection. Subsequently the activity slowly tended to return to control level. Three hours after drug administration, acetylcholinesterase activity inhibition was still 34.1% of control value. In the baboon, the time-course of acetylcholinesterase activity recovery after injection is similar to that recorded in human. The similarity of the time-course of blood acetylcholinesterase activity and changes in smooth pursuit performance suggests a causal relationship between the two factors. A further experiment showed that pyridostigmine administered per os at a dose normally used as a prophylactic against organophosphates does not significantly alter sensorimotor performance as evaluated at the oculomanual tracking system level. When compared to the literature, our results suggest that the baboon can be used as a human experimental analog for pharmacological studies such as the action of acetylcholinesterase inhibitors.

Acetylcholine↗

PubMed1990

Ocular muscle proprioception and visual localization of targets in man.

Passive deviation of one eye through 18 degrees, 30 degrees and 42 degrees, achieved by force applied to a sucked-on contact lens, caused the direction of visual targets seen by the other eye to be misjudged in the direction of the passive movement by an amount roughly one-sixth of the angle of passive deviation. The result was the same when the perceived direction was indicated by hand, as when the instant at which a moving target seemed straight ahead was signalled. This result is interpreted by considering that muscular efferents were identical in normal and eye-deviated subjects. The main difference between the two target localization conditions results from the proprioceptor output of the deviated eye. Our data demonstrate that the assessment of the direction of a target seen by an eye that is free to move depends in part on information received by the brain from proprioceptors in the orbit (in our case the contralateral orbit). It would be surprising if the ipsilateral orbit did not contribute as much or more. We therefore consider that this constitutes clear evidence against the pure outflow theory of visual direction judgement (Helmholz, 1867), additional to that provided by the all-or-nothing situation of complete versus incomplete oculomotor paralysis. Two models have previously been proposed to describe the function of the visual localization mechanism. Both assume that the necessary information is derived from the coding of the position of the eye in the orbit, either through a copy of the muscular activation or through eye muscle proprioception. We propose an alternative model in which both afferent and efferent signals from all actively contracted or stretched muscles provide the necessary information to the CNS. The data gathered so far from normal subjects made strabismic with a suction lens, and from a fair proportion of strabismic patients, support our model describing the mechanism of localization of a single punctate target in darkness.

Adult↗

PubMed1990

Ultrasonic two-axis rotation detector.

A two-axis rotation monitor is described which determines the relative displacement between a pair of ultrasonic detectors using the phase difference of a continuous ultrasound wave generated by a single, distant source. The monitor has been used to measure head rotations around the vertical and horizontal axes, but can easily be adopted to other body segment rotations or translations. The device produces high sensitivity recordings of wide spatial and dynamic range. Although the device is quite linear with good isolation between channels, a computer-based linearization/calibration routine is described which further increases linearity and reduces crosstalk. The device is unobtrusive, inexpensive, and has proven reliable and easy to use.

Equipment Design↗

PubMed1990

Identification of peripheral visual images in a laterally restricted gaze field.

When the peripheral visual field is restricted or distorted, as occurs with certain spectacle lenses, the identification of objects in the periphery requires a coordinated head and eye movement. Initial experiments on the identification of peripheral images under such restrictions show that the degradation in performance is defined by a consistent additional delay in the time required to identify the image correctly. An analysis of the motor movements shows that performance is solely determined by movements of the head; eye movements are sufficiently precise and fast so they do not limit performance. A quantitative model of the identification task was developed and model simulations confirmed the experimental findings that head movement variables, specifically response latency and movement duration, uniquely determine identification performance. Hence, improved performance under these conditions must come from modifications in head-movement control either through training or adaptive processes.

Adult↗

PubMed1989

Mechanisms of short-term saccadic adaptation.

A number of processes have been identified that adaptively modify oculomotor control components. The adaptive process studied here can be reliably produced over a short period of time by a visual stimulus that forces postsaccadic error. This short-term adaptive process, usually termed parametric adaptation, consists of a change in response amplitude that develops progressively over 50 to 100 training stimuli. The resulting compensation is proportional to, but substantially less than, the error induced by the training stimuli. Both increases and decreases in response amplitude can be evoked by an appropriately timed and directed movement of the stimulus target, which forces postsaccadic error. Results show that a single type of training stimulus can influence movements over a broad spatial region, provided these movements are in the same direction as the training stimulus. Experiments that map the range of modification suggest that the increasing adaptive modification operates by remapping final position, whereas the decreasing adaptive modification is achieved through an overall reduction of gain. Training stimuli that attempt to evoke both increases and decreases in the same region show a net modification equivalent to the algebraic addition of individual adaptive processes.

Adolescent↗

PubMed1988

Oculo-manual tracking of visual targets: control learning, coordination control and coordination model.

The processes which develop to coordinate eye and hand movements in response to motion of a visual target were studied in young children and adults. We have shown that functional maturation of the coordination control between eye and hand takes place as a result of training. We observed, in the trained child and in the adult, that when the hand is used either as a target or to track a visual target, the dynamic characteristics of the smooth pursuit system are markedly improved: the eye to target delay is decreased from 150 ms in eye alone tracking to 30 ms, and smooth pursuit maximum velocity is increased by 100%. Coordination signals between arm and eye motor systems may be responsible for smooth pursuit eye movements which occur during self-tracking of hand or finger in darkness. These signals may also account for the higher velocity smooth pursuit eye movements and the shortened tracking delay when the hand is used as a target, as well as for the synkinetic eye-arm motions observed at the early stage of oculo-manual tracking training in children. We propose a model to describe the interaction which develops between two systems involved in the execution of a common sensorimotor task. The model applies to the visuo-oculo-manual tracking system, but it may be generalized to other coordinated systems. According to our definition, coordination control results from the reciprocal transfer of sensory and motor information between two or more systems involved in the execution of single, goal-directed or conjugate actions. This control, originating in one or more highly specialized structures of the central nervous system, combines with the control processes normally operating in each system. Our model relies on two essential notions which describe the dynamic and static aspects of coordination control: timing and mutual coupling.

Adult↗

PubMed1988

Oculo-manual tracking of visual targets in monkey: role of the arm afferent information in the control of arm and eye movements.

The study was aimed at defining the role of hand (and arm) kinaesthetic information in coordination control of the visuo-oculo-manual tracking system. Baboons were trained to follow slow-moving and stepping visual targets either with the eyes alone or with the eyes and a lever moved by the forelimb about the vertical axis. A LED was attached to the lever extremity. Four oculo-manual tracking conditions were tested and compared to eye-alone tracking: Eye and hand tracking of a visual target presented on a screen, eye tracking of the hand, and eye tracking of an imaginary target actively moved by the arm. The performance of the animals evaluated in terms of latency, and velocity and position precision for both eye and hand movements was seen to be equivalent to that of humans in similar situations. After dorsal root rhizotomy (C1-T2) the animals were unable to produce slow arm motion in response to slow-moving targets. Instead, they produced successions of ballistic-like motions whose amplitude decreased as retraining proceeded. In addition, the animals could no longer respond with smooth pursuit eye movements to an imaginary target actively displaced by the animal's forelimb. It was concluded that the absence of ocular smooth pursuit after lesion results from the disruption of a signal derived from arm kinaesthetic information and addresses to the oculomotor system. This signal is likely to be used in the control of coordination between arm and eye movements during visuo-oculo-manual tracking tasks. One cause of the animal's inability to achieve slow arm movement in response to slow target motion is thought to be due to a lesion-induced alteration of the spinal common pathway dynamics which normally integrate the velocity signal descending from the arm movement command system.

Afferent Pathways↗

PubMed1988

Cerebellar involvement in the coordination control of the oculo-manual tracking system: effects of cerebellar dentate nucleus lesion.

When the hand of the observer is used as a visual target, oculomotor performance evaluated in terms of tracking accuracy, delay and maximal ocular velocity is higher than when the subject tracks a visual target presented on a screen. The coordination control exerted by the motor system of the arm on the oculomotor system has two sources: the transfer of kinaesthetic information originating in the arm which increases the mutual coupling between the arm and the eyes and information from the arm movement efferent copy which synchronizes the motor activities of both subsystems (Gauthier et al. 1988; Gauthier and Mussa-Ivaldi 1988). We investigated the involvement of the cerebellum in coordination control during a visuo-oculo-manual tracking task. Experiments were conducted on baboons trained to track visual targets with the eyes and/or the hand. The role of the cerebellum was determined by comparing tracking performance defined in terms of delay, accuracy (position or velocity tracking errors) and maximal velocity, before and after lesioning the cerebellar dentate nucleus. Results showed that in the intact animal, ocular tracking was more saccadic when the monkey followed an external target than when it moved the target with its hand. After lesioning, eye-alone tracking of a visual target as well as eye-and-hand-tracking with the hand contralateral to the lesion was little if at all affected. Conversely, ocular tracking of the hand ipsilateral to the lesion side became more saccadic and the correlation between eye and hand movement decreased considerably while the delay between target and eyes increased. In normal animals, the delay between the eyes and the hand was close to zero, and maximal smooth pursuit velocity was around 100 degrees per second with close to unity gain; in eye-alone tracking the delay and maximal smooth pursuit velocity were 200 ms and 50 deg per second, respectively. After lesioning, delay and maximum velocity were respectively around 210 ms and 40 deg per second, that is close to the values measured in eye-alone tracking. Thus, after dentate lesioning, the oculomotor system was unable to use information from the motor system of the arm to enhance its performance. We conclude that the cerebellum is involved in the "coordination control" between the oculomotor and manual motor systems in visuo-oculo-manual tracking tasks.

Animals↗