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Biomedical subjects

M Jeannerod

Publications and source records attributed to M Jeannerod.

At least 91 records · Page 5Linked to original sources
PubMed1984

The timing of natural prehension movements.

Prehension movements were studied by film in 7 adult subjects. Transportation of the hand to the target-object location had features very similar to any aiming arm movement, that is, it involved a fast-velocity initial phase and a low-velocity final phase. The peak velocity of the movement was highly correlated with its amplitude, although total movement duration tended to remain invariant when target distance was changed. The low-velocity phase consistently began after about 75% of movement time had elapsed. This ration was maintained for different movement amplitudes. Formation of the finger grip occurred during hand transportation. Fingers were first stretched and then began to close in anticipation to contact with the object. The onset of the closure phase was highly correlated to the beginning of the low velocity phase of transportation. This pattern for both transportation and finger grip formation was maintained in conditions whether visual feedback from the moving limb was present or not. Implications of these findings for the central programming of multisegmental movements are discussed.

Journal Article↗
PubMed1984

The control of hand movements in a case of hemianaesthesia following a parietal lesion.

A 46-year-old patient with a lesion limited to the left retrorolandic area without involvement of the prerolandic motor strip was examined. Anaesthesia to tactile, warm, cold, and painful stimuli was complete for the right hand and wrist. Position sense was abolished for the right wrist and finger joints. Performance of the right hand in motor tasks was severely impaired. Simple visual and auditory reaction times were lengthened. Sustaining a constant level of force was impossible. In the absence of visual feedback, only simple, monoarticular movements could be correctly executed; more complex movements requiring coordination between several joints, such as prehension, were poorly, or not, performed. The role of somatosensory cortex in conveying kinaesthetic input to the motor areas and the importance of vision in substituting for kinaesthetic loss, are discussed.

Brain Neoplasms↗
PubMed1983

Effects of unilateral flocculus lesions on vestibulo-ocular responses in the cat.

Unilateral lesions of the cerebellar flocculus were performed in three chronically-implanted adult cats. Following the lesion a spontaneous nystagmus was observed in the dark, with the fast phase directed to the lesioned side. Vestibulo-ocular responses in the dark became asymmetrical. Responses to velocity steps exciting the labyrinth ipsilateral to the lesion were strongly increased. A decrease, although less marked, was observed in the opposite direction. Responses to sinusoidal oscillations in the dark were also asymmetric with respect to both the cumulative eye displacement during rotation in the two directions and the interval between two consecutive reversals of eye movement. These differences were greater at the lower tested frequencies (0.01 HZ) than at the higher (0.1 HZ). Spontaneous nystagmus disappeared in about 10 days and a complete symmetry of the vestibulo-ocular responses was restored in about 3 weeks. It is concluded that a unilateral lesion of the flocculus leads to two separate, but interacting, effects upon vestibulo-ocular responses.

Animals↗
PubMed1982

The role of the flocculus in vestibular compensation after hemilabyrinthectomy.

Unilateral lesions of the cerebellar flocculus were made in two groups of cats chronically implanted for eye-movement recording. In the first group (3 cats), the floccular lesion preceded by 40-70 days a unilateral labyrinthectomy on the contralateral side. In the second group (5 cats), the serial order of the two lesions was reverted, the unilateral flocculectomy following unilateral labyrinthectomy by about 60 days in 2 animals and by 16-27 months in the other 3. The effects of the unilateral labyrinthectomy on the vestibulo-ocular reflex (spontaneous nystagmus and asymmetrical responses) were extensively tested by using natural vestibular stimulations. It was found that recovery from these effects was severely delayed in animals from the first group (flocculectomy prior to labyrinthectomy), although in animals from the second group the flocculectomy secondary to the labyrinthectomy only produced a transient asymmetry of vestibulo-ocular responses. It is concluded that the flocculus is required for initiating (not for maintaining), the compensatory process following peripheral lesions of the vestibular system.

Animals↗
PubMed1982

The coordination of eye, head, and arm movements during reaching at a single visual target.

The time of occurrence of eye, head, and arm movements directed at the same visual target was measured in five human subjects. The latency of activation of the corresponding neck and arm muscles was also measured. It appears that although the overt movements are sequentially ordered (starting with the eye movement, then the head and finally the arm) the EMG discharges are synchronous with respect to the eye movement onset. In addition, eye movement latency appears definitely (though weakly) correlated with either neck or arm EMG latencies. Neck and arm EMG latencies are also mutually correlated. These results indicate a clustering of segmental motor programs for target oriented actions.

Adult↗
PubMed1981

Unidirectional habituation of vestibulo-ocular responses by repeated rotational or optokinetic stimulations in the cat.

1. Unilateral habituation of the vestibulo-ocular reflex was produced in adult cats stimulated by repeated unidirectional velocity steps (vestibular training) or by a continuously moving visual surround (optokinetic training). -- 2. Unidirectional vestibular training produced a strong asymmetry of vestibulo-ocular responses (VOR). Responses to velocity steps applied to the "trained" labyrinth were decreased both in gain and in time-constant. This effect generalized to responses to sinusoidal oscillations (0.03 Hz to 0.1 Hz), i.e. to a stimulus not used during training. -- No spontaneous nystagmus was ever observed in spite of the dynamic VOR asymmetry. -- 3. Unilateral vestibular habituation produced by vestibular training appeared to be a long-lasting phenomenon. It was still present 10 days after the end of training. -- 4. Optokinetic responses were not affected by vestibular training. -- 5. Unidirectional optokinetic training produced an increase in the slow phase velocity of optokinetic nystagmus (OKN) by about 25% in both directions. This effect did not persist for more than a few minutes. A marked spontaneous nystagmus was recorded in the dark after each session of optokinetic training, with a slow phase in the direction opposite to the previous OKN. -- 6. VOR in response to velocity steps and to sinusoidal oscillations were decreased unilaterally after optokinetic training. This effect was of short duration, however, and disappeared within the interval between training sessions. This lack of retention contrasted with the prolonged effect of vestibular training.

Acoustic Stimulation↗
PubMed1981

Effects of unilateral superior colliculus ablation on oculomotor and vestibulo-ocular responses in the cat.

1. Unilateral lesions of the superior colliculus were made in normal cats. Following the operation, animals exhibited a typical neglect for contralateral visual space and forced circling toward the ipsilateral side. Optokinetic nystagmus was decreased for a stimulus moving toward the ipsilateral side, particularly in the temporal-to-nasal direction when the eye contralateral to the lesion was stimulated alone. -- 2. When tested in the dark, animals exhibited a strong imbalance of their vestibulo-ocular responses (VOR) to velocity steps or to sinusoidal oscillations. Rotation of the animal toward the ipsilateral side produced a VOR with a higher gain, and a shorter phase-lead than in pre-operative controls. VOR was decreased in the opposite direction to a smaller extent, however, the overall asymmetry between the two sides at the post-operative stage was about 40%. -- 3. In two animals, spontaneous nystagmus was present in the dark with the fast phase toward the ipsilateral side. -- 4. Visual suppression of VOR was abolished during ipsiversive rotation and was still present during contraversive rotation. -- 5. The effects of unilateral colliculectomy on VOR were transient. Spontaneous nystagmus disappeared in 3 days. VOR asymmetry in the dark was no longer present after 2-3 weeks. Loss of visual VOR suppression persisted for a few more days. -- 6. Superior colliculus exerts a tonic control on static and dynamic components of VOR. This control may mediate part of VOR visual modulation and provide a substitutive input for compensation of pathological VOR asymmetry.

Animals↗
PubMed1981

An attempt at correlating visuomotor-induced tilt aftereffect and ocular cyclotorsion.

Subjects were exposed to an optical rotation of visual reafferences from hand movements. This is known to produce visuomotor adaptation. An experiment is reported where it also induced a perceptual aftereffect measured as a displacement of the apparent vertical and as an ocular cyclotorsion, both in the direction of the optical rotation. No correlation could be found between the two phenomena which can be considered as independent adaptive responses to the visuomotor conflict.

Adaptation, Ocular↗
PubMed1979

Optimal response of eye and hand motor systems in pointing at a visual target. I. Spatio-temporal characteristics of eye and hand movements and their relationships when varying the amount of visual information.

In a task requiring an optimal hand pointing (with regards to both time and accuracy) at a peripheral target, there is first a saccade of the eye within 250 ms, followed 100 ms later by the hand movement. However the latency of the hand movement is poorly correlated with that of the eye movement. When the peripheral target is cut off at the onset of the saccade, there is no correlation between the error of the gaze position and the error of the hand pointing. This suggests an early parallel processing of the two motor outputs. The duration of hand movement does not change significantly when subjects either see or not see their hand (closed or open loop). In the open loop situation, the undershoot of the hand pointing increases with target eccentricity, whatever the subjects are allowed or not to do a saccade toward the target. It suggests that the encoding of eye position by itself is a poor index for an accurately guided movement of the hand.

Adult↗
PubMed1979

Optimal response of eye and hand motor systems in pointing at a visual target. II. Static and dynamic visual cues in the control of hand movement.

The closed loop situation of hand pointing at a target has been experimentally divided into its static and dynamic components. When the subjects see their hand at first (closed loop) until the start of the hand movement cuts off the vision of the hand (open loop), the pointing is significantly more accurate than when it is performed without any vision of the hand before and throughout the movement (fully open loop). This suggests that initial cues as regards hand and target position, improve the motor program by a better identification of initial and final states. As poor as it is, the extra retinal signal (encoding of eye position) improves performance when the foveation is done under closed loop; it allows a better redefinition of target position, and thus modulates the hand motor program through a direct central pathway, which is quicker than the processing of the visual feedback of the hand movement error.

Eye Movements↗
PubMed1979

Vestibulo-ocular responses during the states of sleep in the cat.

The vestibulo-ocular response (VOR) was recorded during natural sleep in cats with chronically implanted electrodes. By using a small amplitude sinusoidal head rotation (11 degrees) peak-to-peak at 0.4 Hz) which elicited only slow compensatory eye movements, the VOR amplitude was found to decrease steeply (down to 40% or less) during slow-wave sleep. The phase of the VOR with respect to head position remained approximately constant. With a larger amplitude of sinusoidal rotation (320 degrees peak-to-peak at 0.05 Hz) the VOR response included nystagmus. During slow-wave sleep, nystagmus disappeared and the overall amplitude of the response decreased. Simultaneously, the phase of the eye response with respect to head position shifted by up to 90 degrees in advance. During paradoxical sleep, VOR disappeared in all cases and was replaced by randomly occurring bursts of rapid eye movements. These results are discussed in terms of a parametric control model of VOR.

Animals↗
PubMed1979

Development of vestibulo-ocular response in the kitten.

Vestibulo-ocular response (VOR) has been recorded in kittens aged between 10 and 61 postnatal days. Responses to velocity steps and to sinusoidal oscillations are present on the earliest recordings, though they are limited to a low gain slow compensatory gaze displacement. Vestibular-induced saccades appear only around postnatal day 30, but adult-like responses with a high gain are not displayed before the end of the second month. Optokinetic nystagmus (OKN) appears earlier (around postnatal day 25) and maturates faster.

Aging↗