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Biomedical subjects

A Berthoz

Publications and source records attributed to A Berthoz.

At least 163 records · Page 9Linked to original sources
PubMed1982

Neuronal activity in prepositus nucleus correlated with eye movement in the alert cat.

1. In nine alert chronically prepared cats the activity of 177 neurons was recorded in the prepositus nucleus during either spontaneous eye movement or that induced by natural vestibular and optokinetic stimulation. 2. In 116 cells, eye position and/or eye velocity was precisely and unequivocally encoded whatever the origin of the eye movement. These cells were separated into different populations according to the eye movement variable encoded and the directionality of the neuronal response. The firing rates of the remaining 61 cells were loosely related to eye movements because a variety of discharge patterns were observed during identical eye movements. In the latter case, some other unmeasured variable (e.g., neck or visual) was suggested to be encoded in the firing frequency. 3. Discharge rate changed before the eyes began to move and reached a new steady level during fixation following a saccade into a particular direction of the orbit. The ondirection was horizontal for 59% of the neurons, vertical for 17%, and oblique for 24%. 4. Regardless of their preferred direction, the discharge rate in 19% of the neurons was closely proportional to eye position. The range in sensitivity was from 1.1 to 7.5 spikes X s-1/deg. Weak velocity responses were occasionally observed during the slow phase of vestibular and optokinetic nystagmus including during saccades. This class of neurons exhibited a very regular interspike interval for a given position of fixation. Since mainly eye position was encoded, these cells were called position neurons. 5. Other prepositus neurons showed both position and velocity sensitivity during saccades and fixation. Their firing rate encoded eye position over the same range as above and also coded velocity during the slow phase of vestibular and optokinetic nystagmus. Depending on the weighting between the position and velocity proportionality constants, these neurons were classified into position-velocity (48%) or velocity-position (33%) groups. 6. The distribution of the above responses led to the conclusion that the prepositus nucleus plays a role in vertical and horizontal spatial integration. The predominance of horizontal activity suggested that the nucleus may be a significant site underlying genesis of horizontal eye position.

Animals↗
PubMed1982

Difference between eye closure and visual stabilization in the control of posture in man.

Stabilizing the visual surroundings of human subjects influences postural control during perturbations of their equilibrium. The latency of the first EMG burst is increased and its amplitude is reduced. Body pitch is 36% stronger than with normal vision. Eye closure does not produce any significant modification of muscular responses and postural performance. This result explains why vision is not considered a rapid source of postural reaction. Eye closure cannot be considered to be visual deprivation.

Electromyography↗
PubMed1981

Differential visual adaptation of vertical canal-dependent vestibulo-ocular reflexes.

Reversing vision in the horizontal (left-right) plane in humans induces adaptive mechanisms and even reversal of the horizontal vestibulo-ocular reflex (HVOR). The present experiments were aimed at investigating if such adaptive modifications could be observed in the frontal plane by reversal of the torsional visual world movements. Torsional vestibulo-ocular reflex (TVOR) was measured in one subject who wore Dove prisms for 19 days. The gain of TVOR was tested in the dark with the head leaned backward and rotating around an earth vertical axis with sinusoidal rotation (1/6 HZ). The gain decreased from 0.27 to 0.13 at 70 degrees peak-to-peak amplitude, and from 0.3 to 0.11 at 45 degrees peak-to-peak amplitude after 19 days of prism-wearing. Full gain recovery was observed 10 days after prism removal. The results are compared with the observation that in the same situation the vertical VOR (up-down) is not reversed (Dove prisms do not reverse visual images in this plane). As the same four (vertical) canals produce both reflexes, it is suggested that central neuronal mechanisms allow the recognition of the geometrical pattern of visual reversals and selectively adapt the reflex in the relevant planes.

Acclimatization↗
PubMed1980

[Inhibitor interneurons of horizontal ocular saccades studied in the alert cat with the aid of intra-axonal injections of peroxidase].

A simultaneous study of the functional and morphological characteristics of burst inhibitory neurons (B.I.N.) has been performed in the alert cat. For the first time, in the central nervous system of mammal, extra- and intracellular records have been coupled with intra-axonal injection of H.R.P. in the alert animal. The B.I.N. discharge during saccades and the quick phase of vestibular and optokinetic nystagmus oriented toward the ipsilateral side of recording. The frequency of discharges is proportional to the eye angular velocity. The axons end on the abducens motoneuron. Collaterals reach the controlateral prepositus hypoglossi nucleus, medial vestibular nucleus and reticular nuclei.

Action Potentials↗
PubMed1980

Eye movement related activity and morphology of second order vestibular neurons terminating in the cat abducens nucleus.

Intracellular records were obtained from axons of second order vestibular neurons in, and around, the left abducens nucleus in alert cats implanted with stimulating electrodes on both vestibular nerves and the left VIth nerve. Twelve secondary vestibular neurons were identified by their increase in firing rate with horizontal head rotation to the left and/or increasing eye position to the right. Following HRP injection, somatic location, axonal trajectory and termination sites were determined. Each of the above cells collateralized extensively in the abducens nucleus in a fashion consistent with their being either inhibitory (n = 7; left) or excitatory (n = 6; right) vestibular neurons in the disynaptic horizontal vestibulo-ocular reflex pathway. These vestibular neurons also arborized extensively in other posterior brainstem eye-movement related areas as well as sending an axon to the spinal cord.

Abducens Nerve↗
PubMed1980

Influence of otolithic stimulation by horizontal linear acceleration on optokinetic nystagmus and visual motion perception.

Several studies in the past have demonstrated the existence of an Otolith-Ocular Reflex (OOR) in man, although much less sensitive than canal ocular reflex. The present paper 1 confirms these previous results. Nystagmic eye movements (L-nystagmus) appear in the seated subject during horizontal acceleration along the interaural axis in the dark for an acceleration level (1 m/s2) about ten times the perception threshold with a sensitivity of about 0.035 rad/m. When sinusoidal linear acceleration is combined with optokinetic stimulation, the recorded nystagmus slow phase velocity exhibits strong periodic modulation related to subject motion. This marked effect of linear acceleration on the optokinetic nystagmus (OKN) appears at a level (0.1 m/s2) close to the acceleration perception threshold and has a 4-fold higher sensitivity than L-nystagmus. Modulation of OKN can reach a peak-to-peak amplitude as great as 20 degrees/s for a given optokinetic field size it increases with the velocity of the optokinetic stimulus, i.e. with the slow phase eye velocity. In parallel with changes in OKN slow phase velocity, linear acceleration induces a motion related decrease in the perceived velocity of the visual scene and modifications in self-motion perception. The results are interpreted in terms of a mathematical model of visual-vestibular interaction. They show that sensory interaction processes can magnify the contribution given to the control of eye movements by the otolithic system and provide a way of exploring its function at low levels of acceleration.

Acceleration↗
PubMed1979

Otolithic-acoustic interaction in the control of eye movement.

In order to examine otolithic contribution to eye movements ten subjects were asked to track either a moving acoustic target or a stationary target during subject linear motion on a cart. The relative displacement between the subject and the target was the same in the two situations. Recordings of eye movements during subject lateral acceleration in the dark without any task, or with the task of tracking an imagined stationary target were made as a control. The frequencies ranged between 0.15 and 0.3 Hz and peak acceleration between 0.55 and 1.2 m/s2. No lateral eye movements (L-nystagmus) were recorded in the dark. Only saccadic eye movements were recorded during the tracking of a moving acoustic target. Slow eye movements interspersed by saccades were observed when the moving subject tracked an imagined or an acoustic stationary target. Contribution of the slow phase to tracking was more important in the presence of an acoustic target than in the presence of imagined target. The results are interpreted in terms of an otolithic contribution to the central reconstruction of the acoustic target velocity, or in terms of an adaptive control of the otolithic-ocular reflex gain. A conceptual model accounting for these interpretations is proposed.

Acoustic Maculae↗
PubMed1979

Dynamic role of vision in the control of posture in man.

The influence of moving visual surround on the manitenance of upright posture has been studied in man during combined motion of a platform (cart) on which subjects were standing. The normal visual surround was either moving together with the cart, or with a velocity equal to cart velocity either in the same or in the opposite direction of car motion (cart acceleration was either 0.2 m/s2 or 0.05 m/s2). The changes in body pitch observed under these three conditions of visual surround motion were in the same direction as those observed when visual surround motion was given in isolation. However, their amplitude was greater, particularly when visual surround motion was in conflict with body motion.

Acceleration↗
PubMed1979

Contribution of vision to muscle responses in monkey during free-fall: visual stabilization decreases vestibular dependent responses.

In a previous study the muscle responses from the lower limbs were studied in the Baboon (Papio-Papio) during sudden falls. On the other hand, recent findings concerning the role of vision in the control of posture during rapid perturbations in man have stimulated the present investigation. EMG activities were recorded from the fully conscious animal using chronic electrodes implanted in various muscles (splenius, quadriceps femoris, soleus, and tibialis anterior). For testing, the monkey was seated in a special chair suspended from an electromagnet and unexpectedly dropped 90 cm. EMG responses were recorded in three randomly presented conditions: with normal motion of visual world (N), with visual world stabilized with respect to the head (S) using a box covered inside by a black and white checkboard pattern surrounding the animal's head, and in total darkness (D). Results showed that condition S is accompanied in all tested muscles by a significant decrease in the EMG response; this effect is particularly evident in the interval 60--120 ms but may occur earlier. Condition D is in most of the cases accompanied by a less important decrease which is situated between condition N and condition S. These results are in contrast to previous concludions of other authors which negated the role of vision in similar situations.

Animals↗
PubMed1979

Electroanatomy of tectal efferent connections related to eye movements in the horizontal plane.

1. Excitatory and inhibitory oligosynaptic pathways from the superior colliculus (CS) to ocular motoneurons engaged in horizontal eye movements were investigated in cats using acute and chronic brain stem transections in combination with intracellular recordings. 2. Isolation of the medial ponto-bulbar tegmentum from vestibular nuclei and adjacent lateral tegmental structures did not impair short-latency EPSPs and IPSPs induced by collicular stimulation in lateral rectus motoneurons (LR-MNs). On the contrary, responses were enhanced after chronic de-efferentation of vestibular nuclei. This suggests compensatory synaptic rearrangement in the tecto-reticulo-abducens pathways. 3. Midsagittal mesencephalic transections eliminated not only crossed excitatory but also ipsilateral inhibitory CS action on LR-MNs indicating that underlying pathways undergo decussation within the midbrain. 4. Midsagittal transections at different pontine and bulbar levels were performed to locate the second decussation of the inhibitory pathway. Ipsilateral IPSPs were eliminated only by deep lesions extending for about 1.5 mm rostral and caudal to the 6th nuclei. 5. Investigation of medial rectus motoneurons (MR-MNs) revealed two types of excitatory responses to CS-stimulation: (a) di- or trisynaptic EPSPs characterized by a fast rising phase and pronounced frequency potentiation; (b) slowly rising EPSPs displaying little or no frequency potentiation. 'Fast' EPSPs were abolished by all types of pontine lesions interrupting transmission through the contralateral 'abducens region' and may thus be relayed by internuclear neurons within or adjacent to the 6th nucleus. 'Slow' EPSPs persisted after transverse sections at midpontine and rostral pontine levels. 6. The trajectory of tectofugal inhibitory pathway to MR-MNs could not be followed due to a marked suppression of IPSPs under pentobarbital anesthesia. Persistence of IPSPs in LR-MNs under same conditions indicated that reciprocal inhibition of LR- and MR-MNs is mediated by different populations of inhibitory interneurons.

Animals↗