Biomedical subjects

M Fabre-Thorpe

Publications and source records attributed to M Fabre-Thorpe.

25 records · Page 2Linked to original sources

PubMed1990

Motor deficit induced by red nucleus lesion: re-appraisal using kainic acid destructions.

The motor deficits induced by red nucleus lesions have been well documented but so far based upon approaches destroying both cells and fibres of passage. In the present study we used kaïnic lesions, which are known to spare, at least partially, the fibres of passage in order to re-investigate the motor deficit induced by rubral lesion. Five cats were fully trained to perform a forepaw pointing movement towards a moving spot of light. Four of them underwent a bilateral neurotoxic lesion of the red nucleus; a fifth one, was used as a control, with the lesion being done electrolytically. Kaïnic lesions induced strong dysmetria with a tendency to over-reaching, and a delayed movement onset; after postoperative training, the dysmetria only persisted when reaching towards targets moving at high speed. The electrolytic lesion led to a much stronger deficit with an additional lengthening of the execution phase duration. Moreover, although overall accuracy could recover, time taken for movement initiation and execution stayed permanently impaired. In the light of these results a distinction can be made between the red nucleus syndrome per se and the one due to damage to fibres of passage.

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PubMed1987

[Modification of the strategy of intentional movement after lesions of the substantia nigra in the cat].

Bilateral lesions of the substantia nigra were carried out in cats previously overtrained at performing a visually guided forepaw movement towards a moving target. Both their reaction time (RT) and movement time (MT) were impaired postoperatively. On the other hand, their pointing precision was unimpaired after lesion and even improved relative to the preoperative level. This improved accuracy persisted even when the duration of the movement had returned to normal. It is suggested that lesioned animals develop and keep a new strategy using visual feed-back throughout the movement, while normal cats, even on such a complex pointing task, mainly use visual information to trigger their movement.

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PubMed1986

Role of the extra-geniculate pathway in visual guidance. I. Effects of lesioning the superior colliculus in the cat.

We investigated the effect of superior colliculus lesions on the performance of a visually guided paw movement. Six cats were trained to perform a paw movement toward a lever moving in front of them at an adjustable speed. The target was visible and accessible for approximately 700 ms, corresponding to the time needed to traverse the aperture situated in front of the animal. To receive a food pellet reward the cat had to press on the lever during this presentation period. Efficient and misguided movements were recorded, and their relative proportions calculated. For each rewarded movement, the response time (delay between the appearance of the lever in the aperture and the cat's press) was automatically computed. After stabilization of their performance, each cat underwent a bilateral electrolytic lesion of the superior colliculi. In all cases it markedly affected precision. The cats first recovered their ability to reach an immobile lever and later on their ability to point to the lever while it was moving. However, even after two months of postoperative training, two cats had still not completely recovered their preoperative precision. All lesioned animals displayed a perturbation in their response time distribution. Anterior lesions, involving area centralis projection, were more effective in producing the deficits than more posterior ones. The results are discussed in relation to the involvement of the superior colliculus in the analysis of peripheral fixed or moving stimuli.

Animals↗

PubMed1986

Role of the extra-geniculate pathway in visual guidance. II. Effects of lesioning the pulvinar-lateral posterior thalamic complex in the cat.

Eight cats were trained to perform a paw movement towards a moving target. The target was a lever which moved at a variable speed across an aperture situated in front of the animal, from left to right or right to left at random, but only once per trial. The animals were trained until performances stabilized in terms of precision (correct movements versus misguided ones) and speed (response time distribution of correctly guided movements). Then they underwent bilateral electrolytic lesions restricted to the pulvinar nucleus (4 cats) or to the lateral posterior nucleus (4 cats). Pre- and postoperative performances were compared. The results showed a clear difference between the two nuclei; postoperative performances after pulvinar lesion were in the preoperative range, both for precision and response time, thus allowing this group to be considered as a control lesion group. On the other hand, a marked impairment in visual guidance followed lateral posterior lesions. This deficit affected both the precision and the speed of the response, with all cats showing a tendency to increase the response time of their efficient movements. This impairment disappeared progressively except for one animal, whose lesion was especially large. We suggest that the nucleus lateral posterior is involved in the control of visually guided movements; and its role as a component of the tecto-thalamo-cortical pathway is discussed.

Animals↗

PubMed1986

Compulsive attentive behavior after lesion of the ventral striatum in the cat: a behavioral and electrophysiological study.

Bilateral lesions of the nucleus accumbens in cat elicited the following changes: preservation in tests requiring focused attention, with difficulty to shift to other targets; paucity of movements, animals displaying moderate hypokinesia and loss of reaction to changes in the environment. These symptoms were accompanied by a significant increase in the amount of beta rhythms, an activity that has been shown to be concomitant with the development of focused attentive behavior. The observed behavioral and electrocortical modifications are opposite those that have been previously obtained in the same species after lesions of the ventral tegmental area.

Animals↗

PubMed1986

Brachium pontis lesions in cats partly reproduce the cerebellar dysfunction of voluntary reaching movements.

The pontocerebellar pathway in the brachium pontis (BP), is known to convey signals from various cortical and subcortical visual structures to the cerebellum. Recently, a cortico-pontocerebellar pathway involving the BP has been implicated in the control of visually guided movements, on the basis of anatomical and physiological data. To further test this hypothesis, using behavioural methods, we studied the effects of a bilateral interruption of these projections in the BP, on 5 cats fully trained to perform a forepaw movement towards a moving target-light. The postoperative deficit consisted of an impairment in precision, with a strong tendency to over-reach and and increase in reaction time, contrasting with an unimpaired movement time. Although there was some initial recovery, performance soon stabilized with a permanent impairment in accuracy and reaction time. These results are discussed in relation to the various sensory signals processed at the pontine level and forwarded to the cerebellum, and compared with the effects of motor dysfunction of cerebellar origin.

Animals↗

PubMed1984

Visually guided movements in the cat: a test using a randomly moving target.

A new apparatus is described in which cats must perform a visually guided movement of the forepaw toward a quasi-randomly moving target in order to obtain a reward. The target is a small bulb fixed to the pen carrier of an XY plotter; it moves under a translucent screen and is only visible to the cat when the bulb comes on at the onset of each trial. Sine waves of variable frequency are applied to the X and Y channels, the resulting target trajectory being a complex Lissajous pattern, unpredictable for the animal. Response times of accurate presses (detected by a capacity detector) are calculated and various types of misreachings can be coded, allowing quantification of performance, and comparison between normal and lesioned cats.

Animals↗