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  • 1
    ISSN: 1432-1106
    Keywords: Key words Thalamus ; Basal ganglia ; Cerebellum ; Electrical stimulation ; Movement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The motor thalamic areas receiving input from the globus pallidus (VA) and the cerebellar nuclei (VL) appear to have different roles in the generation and guidance of movements. In order to further test these differences, we used electrical stimulation to map the ventro-anterior and ventro-lateral nuclei of the thalamus in three ketamine anaesthetised monkeys. Movements were readily evoked from VL at currents of down to 10 μA. The movements were typically multi-joint, and stimulation could evoke arm and trunk or arm and facial movement at the same current threshold. Evoked arm movements often involved multiple joints, with or without finger movements. Facial movements included the lips, tongue, jaw, eyebrows and, occasionally, the eyes. The thalamic map was topographic, but complex with at least two separate regions related to arm movement. Very few sites within the VA could stimulate movement, even at high currents. We therefore suggest that the cerebellar projections to motor regions of the cortex, which pass through the VL thalamic nuclei, have a different relationship and are closer to movement execution than the projections from basal ganglia via the ventro-anterior nucleus.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 65 (1987), S. 455-464 
    ISSN: 1432-1106
    Keywords: Monkey ; Cerebellum ; Cooling ; Local anaesthetic ; Visuo-motor ; Tracking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two monkeys were trained to track a continuously moving target using a joystick. One then had a cooling probe implanted in nucleus interpositus of the cerebellum ipsilateral to his tracking arm. The other had a cannula implanted in the ipsilateral cortex of the lateral cerebellum through which local anaesthetic could be infused. Both monkeys showed similar tracking deficits during temporary inactivation of the cerebellum. The main effects seen were an increase in the peak velocity of their intermittent corrective tracking movements, and a decrease in the accuracy of these movements. Linear regression analyses were undertaken of the peak velocity and amplitude of each corrective movement against a number of possible control signals (target velocity, target position, error, error velocity etc.). The initially strong correlation of the amplitude of each movement made with target velocity was severely reduced during cerebellar inactivation, and movement amplitude became better predicted by the error between target and joystick positions. The peak velocity of movements became more strongly correlated with movement amplitude and less correlated with target velocity than in the intact animal. These results are consistent with the hypothesis that intermittent tracking is achieved by the production of ‘primitive’ movements, that are then adjusted to the correct amplitude and velocity required to catch up with the moving target. Our findings suggest that the cerebellum may normally be responsible for these adjustments, using visual and memorised cues about the target. The velocity of each movement may be reduced, and its amplitude adjusted, by combining measures of the current error with estimates of target speed and direction. We conclude that the cerebellum has an inhibitory role in tuning movements during visuo-motor tasks and that optimal tuning using feedforward measurements of target motion cannot be made without it.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 477-481 
    ISSN: 1432-1106
    Keywords: Key words Visual feedback ; Motor control ; Action tremor ; Parkinson’s disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Visual feedback is one of the key elements in on-line control of smooth manual tracking. To in- vestigate the effects basal ganglia dysfunction have on visual feedback control, we have tested six advanced Parkinson’s disease (PD) patients in comparison with normal controls using visually guided wrist tracking tasks. Tracking performance was assessed under three visual conditions: (1) both guiding target and movement cursor were displayed continuously; (2) the target display was turned off for the second half of each trial; or (3) the cursor display, but not the target, was turned off for the second half of each trial. Thus, for the second half of each trial under conditions 2 and 3, no visual feedback of the relationship between the target and the cursor was available. Results showed that although PD patients had significantly larger tracking errors than controls, and errors significantly increased in both PD patients and controls after withdrawing either visual cue, increases in tracking errors in PD were not significantly different from those in controls. Nor were any significant changes found in the frequency (6–8 Hz) or magnitude of the PD patient’s action tremor after withdrawing visual feedback. These results suggest that on-line movement control of wrist tracking movements in advanced PD is not especially reliant on visual feedback. In conjunction with our previous study of multiple sclerosis (MS) patients, the present results confirm that the basal ganglia is less involved in visual guidance of smooth manual tracking than the cerebellar circuits.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 129 (1999), S. 511-517 
    ISSN: 1432-1106
    Keywords: Key words Parkinson’s Disease (PD) ; Pedunculopontine nucleus (PPN) ; Akinesia ; Kainic acid (KA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The akinesia of Parkinsonism is relieved by pallidotomy and subthalamic nucleotomy, but not by thalamotomy. Therefore, this disabling symptom probably depends upon connections other than the pallidal-thalamocortical tracts, possibly efferents of the medial pallidum descending to the upper brainstem. We have previously demonstrated akinesia in the normal monkey following radiofrequency lesioning in the region of the pedunculopontine nucleus (PPN), one of the primary targets for descending pallidal outflow. Here, we confirm that selectively destroying neurones in the PPN area, whilst sparing fibres of passage, results in an akinetic state in normal macaques.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 682 (1993), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 682 (1993), S. 0 
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Experimental Child Psychology 54 (1992), S. 315-333 
    ISSN: 0022-0965
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Psychology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 96 (1983), S. 173-180 
    ISSN: 1432-1106
    Keywords: Eye movements ; Smooth pursuit models ; Smooth pursuit eye movements ; Time delays ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lisberger's and Robinson's models of smooth pursuit predict very different results from altering retinal feedback delay. We have therefore investigated the effects of increasing the retinal feedback time delay in three normal human subjects by means of an artificial feedback paradigm. When additional delays were incorporated into the retinal feedback path a threshold was reached beyond which the eye exhibited sustained self-excited oscillations or “limit cycles”. The oscillation period increased linearly (as the added delay was increased) with slopes ranging from 1.41 to 1.6 with zero-delay intercepts of between 212 and 306 ms. Contrary to our experimental findings the Robinson and Lisberger models predict that the plot of oscillation period against added delay should have a slope of 3.4 and 2.7 and an intercept of 479 and 554 ms, respectively. Neither model produced comparable limit cycles, both being unstable at delays greater than 280 ms. Our results imply that the models of smooth pursuit need to incorporate predictive control.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 323 (1986), S. 217-221 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Mathematicians, control engineers and information technologists are beginning to take a greater interest in neuroscience. They are perhaps starting to realize that they may be able to learn a few tricks from nature with which to improve their machines. At the same time there is a good chance that ...
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurology 243 (1996), S. 86-90 
    ISSN: 1432-1459
    Keywords: Brain damage ; Diplopia ; Squint ; Hemisphere stroke
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The aim of this study was to investigate the incidence of squint after brain damage. We performed an observational study on 239 consecutive patients admitted to a specialist neurological rehabilitation unit: 129 with stroke, 84 with head injury and 26 with other conditions. Standard orthoptic measures, including visual acuity, cover test, eye movement recording and tests of binocular function were performed. Of all the patients, 89 (37%), were found to have squints, but only 32 of these (36%) experienced double vision. Brain stem lesions causing peripheral ocular motor impairment were found in a high proportion of patients after head injury (56%). Squints were found in 27 of 95 (28%) patients with cortical strokes, many with no other signs of brain stem involvement. Left was just as likely as right hemisphere damage to be associated with squint, but right-sided lesions seemed to protect against diplopia. We conclude that squint is common after brain damage, even if the brain stem is not obviously affected, but only a minority of these patients with acquired squint suffer diplopia.
    Type of Medium: Electronic Resource
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