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F Viallet

Publications and source records attributed to F Viallet.

48 records · Page 3Linked to original sources
PubMed1987

The role of visual reafferents during a pointing movement: comparative study between open-loop and closed-loop performances in monkeys before and after unilateral electrolytic lesion of the substantia nigra.

In order to elucidate the compensatory role of visual feedback during movement, two experiments were designed to compare the motor performances of Papio papio baboons depending on whether the animals were able to visually control the limb trajectory (visual closed-loop condition) or not (visual open-loop condition). The visuomotor task used consisted of making trained pointing movements towards a stationary target. In experiment A, the baboons were successively presented with these two experimental conditions. The abolition of visual control was found to cause no change in either reaction time (RT) or movement time (MT), but brought about extensive pointing errors. It was also associated with a conspicuous increase in the mean velocity and the mean length of the trajectories. In experiment B, two groups of baboons were used. The monkeys in the first group were required to perform under closed loop conditions. The second group performed the pointing movement under open loop conditions. Once criterion was reached by each animal, a unilateral electrolytic lesion of the substantia nigra (SN) was performed. A comparison between the post operative performances of the animals in the two groups showed that suppression of visual cues resulted in a lengthening of the RT and a slowing of the movement speed. Moreover when visual feedback was lacking, the amplitude of the movement decreased and the finger fell short of the target. During the last post operative period, suppression of visual feedback brought about a more rapid return of RTs to their preoperative level and a more durable slowing of movement speed than with normal vision. The discussion deals with the role of visual feed-back in the control of movement preparation and execution, and with the change in mode of motor control caused by lesion of the SN. Partial exclusion of the SN might bring about a shift from the feedforward to a feedback mode relying more heavily on visual cues.

Animals↗
PubMed1987

Performance of a bimanual load-lifting task by parkinsonian patients.

Normal subjects and Parkinsonian patients performed a bimanual load lifting task. In this task, one "postural" forearm, held in a horizontal position while supporting a 1 kg weight, was unloaded either by the experimenter's hand (imposed unloading) or by the subject's other hand in response to a tone burst (voluntary unloading). The variables recorded were reaction time (RT: time interval between the tone and beginning of unloading) and movement time (MT: duration of the change in force measured by a force platform on the "postural" forearm). Elbow angle changes were also measured with a potentiometer. The EMG activity from brachioradialis of the "postural" arm and that from the biceps of the "active" arm were recorded. The Parkinsonian patients showed an increase in both RT and MT and an impairment of the co-ordination between movement and posture which was reflected in an increase in amplitude of the elbow rotation after voluntary unloading. Moreover, the decrease in EMG activity in the brachioradialis of the postural arm during unloading was less in Parkinsonian patients than in the normal group. This disorder of postural command was often accompanied by a lack of anticipatory EMG changes. Comparison between treated and non-treated patients showed that dopamine agonists brought about recovery of both RT and MT but did not improve postural co-ordination. The co-ordination was less impaired when the voluntary unloading was performed by the preferred hand. Several hypotheses are discussed concerning the mechanism underlying this impaired co-ordination.

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PubMed1983

Motor impairment after unilateral electrolytic lesions of the substantia nigra in baboons: behavioral data with quantitative and kinematic analysis of a pointing movement.

Unilateral electrolytic lesions of the substantia nigra (SN) were carried out stereotaxically on 4 baboons which had been previously trained to perform a visually guided pointing movement. For a few days after operation, all animals exhibited a behavioral impairment affecting the contralateral body half and consisting of dystonic flexed posture and akinesia. The animals were thus unable to perform the pointing task with the contralateral hand. After a delay which depended on the extent of the SN lesion, the animals began to make the pointing movement again. Postoperative changes were then observed only on the side opposite the SN lesion. These consisted of an increase in the latency and particularly the duration of the movement without any change in the accuracy. The kinematic analysis of the hand trajectory showed that the contralateral increase in the movement duration corresponded to a regular decrease in the velocities. Study of the recovery over 120 days after SN lesion showed a progressive improvement which was faster with regard to movement duration than to movement latency. These data clearly point to the functional role of the SN in the initiation and particularly in the execution of movement. Quantitative and kinematic analysis of this pointing movement makes it possible to detect and quantify very closely the changes in movement program and execution induced by a SN lesion. This experimental model will be useful for pharmacological in vivo studies allowing a more specific assessment of the functional role of the neurotransmitters involved in SN dysfunction.

Animals↗
PubMed1981

Bradykinesia following unilateral lesions restricted to the substantia nigra in the baboon.

Unilateral lesions were made in the substantia nigra of baboons which had been previously trained to carry out a visually guided pointing movement. During the early post-operative period, the animals were unable to perform the task with the contralateral forelimb because of the severity of the akinesia affecting it. After one or two weeks, the animals began to make the movement; at this time, there was a purely contralateral increase in the latency and particularly the duration of the movement, while its accuracy remained unchanged.

Animals↗
PubMedDate not supplied

[Vascular epilepsy: clinical, electroencephalographic, and computerized tomographic aspects (author's transl)].

The authors report 31 cases of "vascular epilepsy" among 280 cerebral strokes confirmed by cranial computerized tomography. A high incidence of ischemia (28 cases : 90%) is noted. Epileptic seizures are initial (14 cases) or sequellar (17 cases) manifestations of cerebral stroke. Partial seizures are the most frequent (58%), particularly "Jacksonian" motor fits, which, when initial, often lead to status epilepticus. Frequency and bad prognosis of initial status epilepticus are pointed out.

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PubMedDate not supplied

[Capsulo-thalamic hemorrhage (author's transl)].

The authors report clinical and scanographic findings in 26 cases of capsulo-thalamic hemorrhage. They stress the frequency of arterial hypertension as a pre-disposing factor. The clinical picture is represented by the association of disorders of consciousness (usually obnubilation), contralateral flaccid hemiplegia with hemianesthesia, oculomotor disorders (disturbance of vertical gaze, miosis) and disorders of linguistic and motor behaviour. The paraclinical examination of choice is scanography which enables the site, volume and extent of the hemorrhage to be estimated, together with the mass effect and intraventricular rupture. Clinical and scanographic follow-up indicates a favourable prognosis for capsulo-thalamic hemorrhage (77% survival). Follow-up findings point to several unfavourable prognostic factors: immediate coma, persistent and massive flaccid hemiplegia, hemorrhage size exceeding 3 cm, and severe intraventricular rupture. In the light of the data in the literature, the authors discuss the clinical and scanographic signs of capsulo-thalamic hemorrhage.

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PubMedDate not supplied

[Cognition disorders and parkinsonian syndrome: diffuse Lewy body disease?].

A 68 year old man developed progressive cognitive impairment with an akinetic-rigid syndrome which was atypically responsive to levodopa. The patient died after 18 months and the postmortem examination showed typical Lewy bodies in the substantia nigra and pale bodies in the cortex which were unlabelled by ubiquitin antibodies. This case is particular by the neuropathological examination (no immunoreactivity to antibodies against ubiquitin) and by the abnormal response to treatment (dystonia). These two aspects are discussed.

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PubMedDate not supplied

Devic's neuromyelitis optica: a clinicopathological review of the literature in connection with a case showing fatal dysautonomia.

A new clinicopathological case of Devic's neuromyelitis optica, including unusual predominant clinical features (fatal dysautonomia) is described herein: pathological examination showed extensive and severe demyelination mainly involving the optic nerves, the medulla, and spinal cord, which was particularly pronounced in the thoracic segments, and thus explained the unusual vegetative symptomatology. In a review of 45 clinicopathological cases described in the literature as Devic's disease (DD), it turned out that only 22 cases, including the patient described here, fulfilled the recently defined diagnostic criteria [Devic 1980]. Among the other 23 cases, 15 did not fulfill the criteria because of the occurrence of relapses, 3 others had 2 separate pathological locations within the spinal cord, and the remaining 5 showed evidence that a disease other than DD was involved. Among the 22 cases which were definitely taken to be DD, the mean age at clinical onset was 39 years (+/- 14); it was characterized by acute bilateral visual loss and transversal myelitis which gradually led either to death or to partial or complete recovery. The pathological lesions, which mostly were located along the optic tracts and the spinal cord, were characterized by demyelination with inflammation and necrosis; in some cases the pathological process diffused into the medulla (8/22 cases) or the whole brainstem (4/22 cases). The cavitation of the spinal cord was not a key feature of the diagnosis, since it was observed on only 9/22 cases. Devic's neuromyelitis optica may be a separate nosological entity which differs from multiple sclerosis.

Autonomic Nervous System Diseases↗