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  • 1
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    German Medical Science; Düsseldorf, Köln
    In:  Evidenzbasierte Medizin - Anspruch und Wirklichkeit; 102. Jahrestagung der Deutschen Ophthalmologischen Gesellschaft; 20040923-20040926; Berlin; DOC04dogSA.10.07 /20040922/
    Publication Date: 2004-09-21
    Keywords: ddc: 610
    Language: English
    Type: conferenceObject
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  • 2
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 126 (1999), S. 19-30 
    ISSN: 1432-1106
    Keywords: Key words Motor control ; Arm movement ; Reaching ; Posture ; Gaze ; Hand-eye coordination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The analysis of errors in two-joint reaching movements has provided clues about sensorimotor processing algorithms. The present study extends this focus to situations where the head, trunk, and legs join with the arm to help reach targets placed slightly beyond arm’s length. Subjects reached accurately to touch ”real targets” or reached to the remembered locations of ”virtual targets” (i.e., targets removed at the start of the reach). Subjects made large errors in the virtual-target condition and these errors were analyzed with the aim of revealing the implications for whole-body coordination. Subjects were found to rotate the head less in the virtual-target condition (when compared with accurate movements to real targets). This resulted in a more limited range of head postures, and the final head angles at the end of the movements were geometrically related to the incorrect hand locations, perhaps accounting for some portion of the errors. This suggests that head-eye-hand coordination plays an important role in the organization of these movements and leads to the hypothesis that a representation of current gaze direction may serve as a reference signal for arm motor control.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 20 (1974), S. 385-401 
    ISSN: 1432-1106
    Keywords: Neck afferents ; Cerebellum ; Climbing fiber ; Mossy fiber ; Purkinje cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Afferent information from the neck plays an important role in the regulation of posture and the control of head and eye movements. The present series of experiments was designed in order to characterize the cerebellar projections of neck afferents in the cat. Both anesthetized and decerebrate animals were used, and recordings were obtained following electrical stimulation of the second cervical dorsal root (C2). 2. Following electrical stimulation of C2 dorsal root, field potentials were recorded in lobules V and VI. Amplitude was maximum in the lateral third of the ipsilateral lobule V. These field potentials were produced by combined mossy and climbing fiber (MF and CF) volleys arriving at the cerebellar cortex with different latencies: 8 msec for MF and 24 msec for CF (mean values). The threshold for electrical stimulation was lower for MF than for CF activation; CF responses were evoked by high threshold afferents from muscle and joint receptors. 3. A comparison was made between the latencies of cerebellar responses evoked by electrical stimulation of nuchal and other afferents (vestibular nerve, fore-and hindpaw). The latencies of MF responses vary widely, while those of the CF responses show a much smaller variation. 4. Projection of the afferents from the neck was also demonstrated in the pars intermedia at the limit of the caudal folium of lobule V and of lobule VI (lobule simplex). A study of the convergence to this portion of pars intermedia demonstrated that stimulation of extraocular muscle nerves, trigeminal nerve, and fore-and hindpaws, as well as the neck afferents, generates a strong localized CF response with actual convergence onto single Purkinje cells. The recordings suggest that this area of wide convergence on CFs is not restricted to the superficial cortex, but extends through the depth of the fissura prima. Implications of these findings, in relation to the functional organization of lobule VI and the fissura prima, are discussed.
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  • 5
    ISSN: 1432-1106
    Keywords: Key words Omnipause neurons ; OPN ; Saccade ; Gaze shift ; Tracking ; Perisaccadic drifts ; Moving target ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Pontine omnipause neurons (OPNs) have so far been considered as forming a homogeneous group of neurons whose tonic firing stops during the duration of saccades, when the head is immobilized. In cats, they pause for the total duration of gaze shifts, when the head is free to move. In the present study, carried out on alert cats with fixed heads, we present observations made during self-initiated saccades and during tracking of a moving target which show that the OPN population is not homogeneous. Of the 76 OPNs we identified, 39 were found to have characteristics similar to those of previously described neurons, ”saccade” (S-) OPNs: (1) the durations of their pauses were significantly correlated with the durations of saccades; (2) the discharge ceased shortly before saccade onset and resumed before saccade end; (3) visual responses to target motion were excitatory; and (4) during tracking, S-OPNs interrupted the discharge for the duration of saccades and resumed firing during perisaccadic ”drifts”. However, the characteristics of 37 neurons (”complex” (C-) OPNs) were different: (1) the pause duration was not correlated with the duration of self-initiated saccades; (2) time lead of pause onsets relative to saccades was, on average, longer than in the group of S-OPNs, and firing resumed after the saccade end; (3) visual target motion suppressed tonic discharges; and (4) during tracking, firing was interrupted for the total duration of gaze shifts, including not only saccades but also perisaccadic ”drifts”. We conclude that cat OPNs can be subdivided into two main groups. The first comprises neurons whose firing patterns are compatible with gating individual saccades (”saccade” OPNs). The second group consists of ”complex” OPNs whose firing characteristics are appropriate to gate total gaze displacements rather than individual saccades. The function of these neurons may be to disinhibit pontobulbar circuits participating in the generation of saccade sequences and associated perisaccadic drifts.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1106
    Keywords: Eye movements ; Lateral rectus motoneurons ; Medial rectus motoneurons ; Colliculus superior ; Tecto-oculomotor pathways ; Brainstem lesions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 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.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1106
    Keywords: Adaptation ; Vestibulo-ocular reflex ; Torsional eye movements ; Prism reversal ; Visual vestibular interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 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 ° peak-to-peak amplitude, and from 0.3 to 0.11 at 45 ° 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.
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  • 8
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular reflex ; Plasticity ; Adaptation ; Visual-vestibular interaction ; Pursuit ; Mental training
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The vestibulo-ocular reflex (VOR) can be suppressed in darkness if a subject tries to imagine that he looks at a head fixed target. This mental suppression of VOR was used to induce adaptive changes in VOR gam during 3 h of active head oscillations in complete darkness. VOR gain changes were tested by asking the subject to look at a visual target; then passively or actively the head was turned in darkness while the subject “fixated” the same target. Corrective saccades occurring at the end of the movement when lights were turned on give an elegant measure of VOR gain. Three hours of training induced in 3 subjects a mean of 10.9% and 11.4% decrease of VOR gain for passive and active conditions, respectively. This demonstrates that reflex adaptation can be obtained without external cues, and probably with only an internal reconstruction of target and eye movement.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-1106
    Keywords: Visuo-motor behavior ; Saccades ; Tecto-reticulo-spinal neurons ; Intracellular HRP ; Repetitive firing ; Burst neurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Activity of tecto-reticulo-spinal neurons (TRSN), identified electrophysiologically and/or by intra-axonal HRP injections, was studied in alert cats during presentation of moving visual stimuli. A majority of TRSNs showed complex visuomotor properties: directionally selective visual responses in the absence of motor counterparts of orienting, enhanced bursting when stimuli triggered saccades, and no activation for spontaneous saccades. Highest intraburst frequencies were observed during active orienting towards novel, “interesting” objects. The more vigorous bursts usually contained repetitive grouped discharges attaining instantaneous frequencies up to 700 imp/s but average firing rates remained in the range of 120–300 imp/s. Intra-axonal HRP injections confirmed terminations of TRSN collaterals in the premotor areas of the lower brain stem, including the abducens nucleus, but also disclosed differences in the details of collateralization between neurons showing different types of visuo-motor activity.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 69 (1988), S. 399-406 
    ISSN: 1432-1106
    Keywords: Neck muscles ; Oculo-motor system ; Reticulo-spinal system ; Motoneurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A tonic coupling between the horizontal component of eye position and dorsal neck muscle activity has been demonstrated in the cat and monkey. In order to demonstrate this synergy in humans and study its characteristics, we have measured the relation between the firing rate of individual motor unit of the splenius muscle and voluntary horizontal shifts of gaze using 5° steps, in head-fixed subjects. Eye movement recording was achieved by conventional binocular electro-oculography and the activity of the right splenius muscle was recorded with Bronks coaxial bipolar electrodes inserted manually at the C4–C5 intervertebral level. The activity of 51 motor units in 10 subjects has been recorded. For all subjects, motor units firing rate increased when the gaze shifted to the ipsilateral side, and both increase in firing rate and recruitment were observed. These results demonstrate that the tonic eye head synergy is also present in man.
    Type of Medium: Electronic Resource
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