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Biomedical subjects

A Berthoz

Publications and source records attributed to A Berthoz.

At least 145 records · Page 8Linked to original sources
PubMed1987

Reticulo-spinal neurons participating in the control of synergic eye and head movements during orienting in the cat. I. Behavioral properties.

The activity of 24 reticulo-spinal neurons (RSN) identified by antidromic stimulation at the C1-C2 level has been recorded intra-axonally in the pons of alert head-fixed cats during spontaneous gaze shifts and orienting towards novel targets. Relationship of neuronal discharge to saccadic eye movements, positions of fixation and EMG of dorsal neck muscles were analysed. The present report describes behavioral properties of a group of 14 RSN showing similar types of correlations with motor parameters during eye-head synergies. These "eye-neck" RSN (EN-RSN) generate bursts in synchrony with phasic components of ipsilateral neck EMG and leading ipsiversive saccades by a variable lead time. Bursts are followed by a prolonged discharge whose frequency decays even when eccentric eye position is maintained constant and accompanied by sustained neck muscle activity. The firing rate of EN-RSNs depends on eye position: they are silent with saccades in their ON-direction when the eyes are deviated towards the contralateral half of the oculomotor range and the ipsilateral neck muscles are relaxed. When the eyes cross the vertical meridian, the frequency of phasic and tonic components related to eye-head synergies increase proportionally to ipsilateral eye position. Ten of the 14 EN-RSNs, located in the pontine reticular formation, received monosynaptic input from the contralateral superior colliculus. Two were labeled by intra-axonal injection of HRP which revealed extensive branching in the abducens, facial, medial and lateral vestibular, prepositus and intercalatus nuclei and in the caudal pontine and bulbar reticular formation. It is concluded that the caudal pontine tegmentum, including the region just anterior to the abducens nucleus, contains RSNs whose signals seem appropriate to control phasic neck muscle activity and which also project to structures related to ocular and facial movements. Comparisons with the perisaccadic activity of tectal neurons projecting in the predorsal bundle reveals a profound transformation of the descending signal at the level of EN-RSNs which represent first order relay neurons of the tecto-reticulo-spinal pathway.

Action Potentials↗
PubMed1987

Reticulo-spinal neurons participating in the control of synergic eye and head movements during orienting in the cat. II. Morphological properties as revealed by intra-axonal injections of horseradish peroxidase.

Previously we described physiological properties of pontine reticulo-spinal neurons which generate bursts and decaying tonic discharges related to eye movements and neck muscle activity during ipsiversive gaze shifts (Grantyn and Berthoz 1987). Two of these "eye-neck reticulo-spinal neurons" (EN-RSN) were labeled by intra-axonal injections of HRP. The present report provides a detailed description of their morphology with an emphasis on the topography of axon collaterals, bouton numbers, and the structure of preterminal ramifications in different target areas. The cell bodies of labeled EN-RSNs were located rostro-ventrally to the abducens nucleus. Their descending axons issued 8 and 13 collaterals (left and right EN-RSN, respectively) at different rostro-caudal levels, between the abducens nucleus and the pyramidal decussation. On the basis of the size of their cell bodies, the isodendritic type of dendritic branching and their multiple collateralization, EN-RSNs correspond to the class of "generalized" reticular neurons, often referred to as The Scheibels' neurons. Collaterals of EN-RSNs terminated in the following structures: the abducens and facial nuclei, the medial and lateral vestibular nuclei, the nn. prepositus and intercalatus, and the bulbar reticular formation. As judged from bouton numbers, the strongest connection of both neurons was with the abducens nuclei. Terminations in the rostral part of the medial vestibular and prepositus nuclei indicate that EN-RSNs may also influence oculomotor output activity through these indirect routes. In the facial nucleus, a majority of terminations was found in its medial subdivision containing motoneurons of ear muscles. However, other subdivisions were also contacted by EN-RSNs. Most terminations in the rostral bulbar reticular formation are distributed to the dorsal, gigantocellular field. Within this field, there is a substantial contribution to the zone characterized by the highest density of reticulo-spinal neurons projecting directly to neck motoneurons. Other target areas which may participate in the modulation of spinal cord activity by EN-RSNs are the ventral reticular nucleus in the caudal medulla and the lateral vestibular nucleus. EN-RSNs also establish connections with precerebellar structures: the prepositus and the paramedian reticular nuclei. The numbers of boutons on collaterals issued within 6 mm of the injection site varied between 37 and 469. The occurrence of presumed axo-somatic contacts was low (0-8.2%) and not characteristic for any particular target area. Local accumulations of boutons in the form of small and large field clusters was a common observation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Modulation by eye position of neck muscle contraction evoked by electrical labyrinthine stimulation in the alert cat.

Modulation of vestibulo-spinal reflexes by gaze is a model system for studying interactions between voluntary and reflex motor activity. In the alert cat, the EMG of Splenius and Obliquus capitis muscles increases with ipsilateral gaze eccentricity during spontaneous eye movements. Labyrinth stimulation by current pulses evokes EMGs with latencies consistent with a three neuron vestibulocollic pathway. The amplitude of evoked activity increases with eye position. The directions in which eye movements increase EMG was usually the same for both spontaneous and induced EMG activity, namely, horizontal and ipsilateral. However, sometimes the increase in spontaneous EMG occurred with horizontal eye position, whereas the induced EMG changed with vertical eye position. Spontaneous and evoked EMG are then modulated by different eye position signals. Command signals reflecting eye position probably reach two different types of neurons in the vestibulo-collic pathway, most likely secondary vestibular neurons and neck muscle motoneurons.

Animals↗
PubMed1987

Adaptive changes in perception of body orientation and mental image rotation in microgravity.

The perception of the subjective body orientation with respect to a foot reference basis, and the adaptation of mental image rotation have been investigated before, during, and after a 7-d spaceflight. The findings show that the body is tilted forward in darkness and in stabilized vision, which indicates a predominant role of vision in such orientational tasks performed in microgravity. Furthermore, perception of head angular rotation in pitch and roll axes seems to be altered in microgravity, whereas head displacements in yaw are estimated correctly. Subjects' capability to rotate mentally the image of the visual environment increased during the flight. Memorized writing was affected in microgravity, especially concerning the layout of letters corresponding to the vertical direction.

Adaptation, Physiological↗
PubMed1986

Some collicular efferent neurons code saccadic eye velocity.

The activity of identified tecto-reticulo-spinal neurons (TRSNs) was studied in alert head-fixed cats during orienting towards moving visual stimuli. Eye movements and dorsal neck muscle activity were recorded simultaneously. Burst parameters of TRSNs showing visuomotor properties were analysed quantitatively. It could be demonstrated that some neurons generate presaccadic bursts whose instantaneous frequency profile is closely correlated with the profile of saccadic eye velocity. This correlation could be revealed only under conditions in which cats made orienting saccades to 'catch' a target moving in the preferred direction of the neuron's visual receptive field. Latency between bursts and saccades varied depending upon the degree of attention toward the target and saccade direction.

Animals↗
PubMed1986

Modifications of gain asymmetry and beating field of vertical optokinetic nystagmus in microgravity.

Optokinetic nystagmus (OKN) was measured in human subjects before, during and after exposure to microgravity induced by either parabolic flight or space flight. The downward (slow phase up) OKN gain was greater than upward gain in normal gravity. On first exposure to microgravity this asymmetry was reversed. In addition, the beating field of OKN tended to shift downward, and the vertical optokinetic after nystagmus (OKAN) time constant was increased. This reversed asymmetry disappeared after 3 days of space flight. On return to 1 g gravity, there was a general drift of the eye in the upward direction during either spontaneous eye movements or OKN. This suggests that the sacculus normally influences mean vertical eye position and the perception of the subjective horizontal direction, both of which are gravity dependent.

Electrooculography↗
PubMed1986

The orientation of the cervical vertebral column in unrestrained awake animals. I. Resting position.

The orientation of the cervical vertebral column was studied by X-ray photography of the region containing the head and the neck in nine unrestrained species of vertebrates (man, monkey, cat, rabbit, guinea pig, rat, chicken, frog, lizard). In addition, the orientation of the horizontal semicircular canals was measured in four species using landmarks on the skull. In all vertebrates studied, with the exception of frog and lizard, the general orientation of the cervical vertebral column was vertical when animals were at rest, and not horizontal or oblique as suggested by the macroscopic appearance of the neck. The posture of the animal, whether lying, sitting or standing, had little effect on this general vertical orientation, although some variability was noticed depending on the species. This finding prompted the definition of a resting zone, where the cervical column can take any orientation within a narrow range around a mean position. The cervical vertebral column composes part of the S-shaped structure of the entire vertebral column, with one inflection around the cervico-thoracic (C7/Th1) junction. This feature is already noticable in the lizard. The vertical orientation of the cervical vertebral column is interpreted to provide a stable and energy saving balance of the head. Furthermore, when the head is lowered or raised, the atlanto-occipital and cervico-thoracic junctions are predominantly involved, while the entire cervical column largely preserves its intrinsic configuration. The curved configuration of the cervico-thoracic vertebral column embedded in long spring-like muscles is interpreted to function as a shock absorber. At rest, animals did not hold their heads with the horizontal canals oriented earth horizontally all the time, but often maintained them pitched up by ca. 5 deg, as has been reported for man. At other times, presumably when the vigilance level increased, the horizontal canals were brought into the earth horizontal plane. The vertical orientation of the cervical column results in a vertical positioning of the odontoid process of the axis (second cervical vertebra, C2), which thus provides the axis of rotation for yaw movements of the head. This axis corresponds to that of the horizontal semicircular canals. The vertical organization of the cervical vertebral column in birds and mammals, whether the animal is quadrupedal or bipedal, points to a common organizational principle for eye and head movement systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

European vestibular experiments on the Spacelab-1 mission: 5. Contribution of the otoliths to the vertical vestibulo-ocular reflex.

The gain of the vestibulo-ocular reflex in the sagittal plane may be due to a cooperation between otoliths and the vertical semi-circular canals. The present space experiment was aimed at studying the influence of the absence of gravity stimulation on the otoliths, by comparing VOR gain and phase in space and on ground. Measurements were taken the 5th and the 7th day of flight, the subject being asked to perform, eyes closed, active head oscillations in pitch while fixating an imaginary target in front of him. No significant decrease of the VOR gain was found in space, but a change in phase was noted. A significant increase of the VOR gain was found 14 h after landing. Control experiments have been done on ground on several subjects. They indicate that pitch VOR gain during active head movements is about one, with eyes open in darkness at 1 Hz.

Adaptation, Physiological↗
PubMed1985

Burst activity of identified tecto-reticulo-spinal neurons in the alert cat.

Activity of tecto-reticulo-spinal neurons (TRSN), identified electrophysiologically and/or by intra-axonal HRP injections, was studied in alert cats during presentation of moving visual stimuli. A majority of TRSNs showed complex visuomotor properties: directionally selective visual responses in the absence of motor counterparts of orienting, enhanced bursting when stimuli triggered saccades, and no activation for spontaneous saccades. Highest intraburst frequencies were observed during active orienting towards novel, "interesting" objects. The more vigorous bursts usually contained repetitive grouped discharges attaining instantaneous frequencies up to 700 imp/s but average firing rates remained in the range of 120-300 imp/s. Intra-axonal HRP injections confirmed terminations of TRSN collaterals in the premotor areas of the lower brain stem, including the abducens nucleus, but also disclosed differences in the details of collateralization between neurons showing different types of visuo-motor activity.

Animals↗
PubMed1984

Effects of rectilinear acceleration and optokinetic and caloric stimulations in space.

During the flight of Spacelab 1 the crew performed a number of experiments to explore changes in vestibular function and visual-vestibular interactions on exposure to microgravity. Measurements were made on the threshold for detection of linear oscillation, vestibulo-ocular reflexes elicited by angular and linear movements, oculomotor and posture responses to optokinetic stimulations, and responses to caloric stimulation. Tests were also conducted on the ground, during the 4 months before and on days 1 to 6 after flight. The most significant result was that caloric mystagmus of the same direction as on the earth could also be evoked in the weightless environment.

Acceleration↗
PubMed1984

Adaptive modification of the vestibulo-ocular reflex by mental effort in darkness.

The vestibulo-ocular reflex (VOR) can be suppressed in darkness if a subject tries to imagine that he looks at a head fixed target. This mental suppression of VOR was used to induce adaptive changes in VOR gain during 3 h of active head oscillations in complete darkness. VOR gain changes were tested by asking the subject to look at a visual target; then passively or actively the head was turned in darkness while the subject "fixated" the same target. Corrective saccades occurring at the end of the movement when lights were turned on give an elegant measure of VOR gain. Three hours of training induced in 3 subjects a mean of 10.9% and 11.4% decrease of VOR gain for passive and active conditions, respectively. This demonstrates that reflex adaptation can be obtained without external cues, and probably with only an internal reconstruction of target and eye movement.

Adaptation, Physiological↗
PubMed1984

Gaze changing behaviour in head restrained monkey.

The electromyographic activity of neck muscles and head torque were recorded in the alert, head-fixed rhesus monkeys together with the horizontal component of eye movements during pursuit movements, scanning movement and vestibular stimulation in darkness. A strong correlation between head torque and the horizontal component of eye position was demonstrated during these three different experimental situations. These conjugate head and eye movements are accompanied by a specific change in the timing of neck neuromuscular activation.

Acoustic Stimulation↗
PubMed1984

The European vestibular experiments in Spacelab-1.

A series of experiments were performed in the Spacelab-1 mission on November/December, 1983, pre-, in-, and postflight. These experiments covered various aspects of the functions of the vestibular system, the inflight tests comprising threshold measurements for linear movements in three orthogonal axes, optokinetic stimulation, vestibulo-ocular reflexes under linear and angular accelerations, caloric stimulation with and without linear accelerations; pre- and postflight tests repeated the inflight protocol with the addition of subjective vertical and eye counter-rotation measurements using a tilt table. One of the most surprising and significant results was the caloric test: strong caloric nystagmus on the two subjects tested was recorded inflight; this was contrary to what was expected from Barany's convection hypothesis for caloric nystagmus.

Adaptation, Physiological↗
PubMed1983

Eye and neck motor signals in periabducens reticular neurons of the alert cat.

The purpose of this work was to search for neurons in the ponto-medullary reticular formation which can carry horizontal eye position signals to dorsal neck muscles of the cat. The recordings were localized in an area of the ponto-medullary reticular formation which contains reticulo-spinal neurons projecting to the neck (Peterson et al. 1980). Experiments were performed on alert, head-fixed cats. Eye movements were measured by the search-coil technique. Neuronal activity was recorded extracellularly with glass microelectrodes. Neurons were localized both by stereotaxic coordinates and by their position with respect to the antidromic field potential profile of the abducens nucleus. EMG of longissimus capitis, obliquus capitis and splenius muscles were recorded. Vestibular stimulation was produced by a turn-table. Reticular cells were found below the abducens nucleus (1 to 3.5 mm below the center of the nucleus, A.P.:5.3 to 7.2 mm;L: 1 to 1.5 mm) showing a firing rate closely related to EMG during spontaneous saccades and, to a variable degree, to the ipsilateral horizontal component of eye position. 'Tonic' and 'burst-tonic' cells were found. During vestibular stimulation, the firing rate kept the same relationship with eye position and neck EMG. It is concluded that the analyzed reticular cells are good candidates to be reticulo-spinal neurons which mediate a signal allowing a synergistic movement of head and eye during orientation in the horizontal plane.

Abducens Nerve↗