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  • 1
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    German Medical Science; Düsseldorf, Köln
    In:  27. Deutscher Krebskongress; 20060322-20060326; Berlin; DOCPO274 /20060320/
    Publication Date: 2006-04-21
    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
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular reflex ; Velocity storage ; Head reorientation ; Semicircular canals ; Otolith organs ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The otolith-semicircular canal interaction during postrotatory nystagmus was studied in ten normal human subjects by applying fast, short-lasting, passive head and body tilts (15, 30, 45, or 90° in the roll or pitch plane) 2 s after sudden stop from a constant-velocity rotation (100°/s) about the earth-vertical axis in yaw. Eye movements were measured with three-dimensional magnetic search coils. Following the head tilt, activity in the semicircular canal primary afferents continues to reflect the postrotatory angular velocity vector in head-centered coordinates, whereas otolith primary afferents signal a different orientation of the head relative to gravity. Despite the change in head orientation relative to gravity, postrotatory eye velocity decayed closely along the axis of semicircular canal stimulation (horizontal in head coordinates) for large head tilts (90°) and also for small head tilts (15–45°) for reorientations in the pitch plane. Only for small head tilts (15–45°) in the roll plane was there a reorientation of the eye rotation axis toward the gravitational vector. This reorientation was approximately compensatory for 15° head tilts. For 30° and 45° head tilts the eye rotation axis tilted toward the gravitational vector by about the same amount as for 15° head tilts. These results suggest that, with the exception of small head tilts in the roll plane, there was no compelling data showing a relationship between the eye rotation axis and head tilt and that postrotatory nystagmus is largely organized in head-centered rather than gravity-centered coordinates in humans. This indicates a rudimentary, nonlinear, and direction-specific interaction of semicircular canal and otolith signals in the central vestibular system in humans.
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  • 4
    ISSN: 1432-1106
    Keywords: Eye movements ; Neglect ; Egocentric space representation ; Parietal brain lesion ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We recently argued that the specific compensation of spatial neglect by manipulating neck proprioceptive and vestibular input is due to a central “correction” of the disturbed neural transformation process converting the afferent input coordinates from the peripheral sensory organs into a central representation of egocentric space. Both types of stimulation were proposed to induce a reorientation of the deviated or distorted egocentric spatial reference frame. The aim of the present study was to observe this process of reorientation under a condition in which no visual stimulus can attract the subject's attention and thus influence exploration behaviour from outside. We recorded eye movements of normal subjects and of three patients with spatial neglect after right parietal lesions while searching for a non-existent target in complete darkness. It was assumed that the area of the outer space that subjects spontaneously explore under this condition is a direct function of the subject's representation of egocentric space. Ocular space exploration was biased and confined almost entirely to the right side of the midsagittal plane in patients with neglect. This spatial distribution of exploratory eye movements changed remarkably with left-sided neck muscle vibration as well as with left-sided vestibular stimulation using ice water calorics. The spatial area of exploration was significantly enlarged to the contralesional side and the exploration maximum shifted in the same direction. Whereas with both types of stimulation space exploration of patients with neglect was similar to that of normal subjects when not being stimulated, neck proprioceptive and vestibular stimulation in normal subjects induced a quasi neglect-like exploration pattern, i.e. a bias to one side of the objective midsagittal plane. If ocular space exploration was, however, related to the subjectively perceived position of the midsagittal plane in space, eye movements were symmetrically distributed and carried out to both sides of subjective “straight ahead” in all experimental conditions, in normal subjects as well as in patients with neglect. The present results support the above hypothesis and indicate that neck proprioceptive as well as vestibular input directly contribute to the computation of the subject's central representation of egocentric space used for localizing body orientation and for guiding motor behaviour in space.
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  • 5
    ISSN: 1432-1106
    Keywords: Ocular stability during head turning ; Eye-head coordination ; Vestibulo-ocular reflex ; Neck-ocular reflex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Since during active eye-head turning the eyes move first and with higher velocity than the head, the lines of sight reach the target while the head is still moving. Then for the remaining duration of the head movement the eyes maintain their fixation by performing a movement which is counter to that of the head and perfectly compensates for it. It is agreed that this compensatory eye movement is critically influenced by visual, vestibular and neck afferents and that it is not initiated centrally. We have investigated a) the relative contribution of the vestibular and neck afferents to the compensatory eye movement made during active and passive head turning in monkeys and b) the mechanisms underlying the recovery of compensatory eye movements following either the removal of the vestibular or neck loop or both. Our results have shown that 1. normal monkeys display perfect ocular stability in darkness, 2. at least 95% of ocular stability is due to the vestibular loop, and 3. the contribution of the neck loop is negligible. Following bilateral vestibulectomy the recovery of compensatory eye movements occurs gradually and reaches 90% within seven weeks but only during active head movements. We have shown that there are at least three mechanisms underlying this recovery: 1. an increase in gain of the neck loop. 2. the occurrence of a centrally programmed compensatory eye movement, and 3. a recalibration of the saccadic and head motor system.
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  • 6
    ISSN: 1432-1106
    Keywords: Vestibular nuclei ; Optokinetic responses ; Visual-vestibular interaction ; Goldfish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The responses of vestibular nuclei neurons of relaxed unaesthetized goldfish have been examined with trapezoid velocity stimuli under three conditions. Responses to horizontal body rotation in the dark (pure vestibular stimulation) resemble those observed in vestibular nerve afferents. Optokinetic responses to exclusive visual surround-motion are also direction-specific and, in contrast to vestibular responses, exhibit a tonic response to constant velocity. They show three different response profiles, classified A, B or C, based on the neuron's discharge rate: either increasing, decreasing or remaining constant once surround motion is maintained at constant velocity. Following these dynamic effects, optokinetic responses have a maintained modulation of resting discharge until deceleration commences. The time constants associated with the dynamic effects vary between 1 and 11 seconds. Steady-state modulation of optokinetic responses shows a weak relation to stimulus velocities exceeding 10 deg/sec. Responses to body rotation in the light were found to linearly combine the weighted vestibular and optokinetic responses so that accurate velocity information is available for sensory and motor functions independent of the neuron's vestibular (I, II) or optokinetic (A, B, C) response type. The principle of this visual-vestibular interaction is discussed with respect to multisensory processing within the vestibular nuclei.
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  • 7
    ISSN: 1432-1106
    Keywords: Human balancing ; Spinal stretch reflex ; Leg muscle EMG ; Proprioceptive posture control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary While subjects balanced on a seesaw consisting of a platform with a curved base, the antero-posterior sway of head and body as well as changes in the angle of the ankle joint were recorded and analysed for their frequency power spectrum. The EMG of leg muscles and the position of the resultant force exerted by the seesaw on a force-measuring platform were simultaneously registered and analysed. Balancing oscillations of 4–5 Hz were observed under this condition. They were accompanied by short, reciprocally organized bursts of EMG activity in the leg muscles. When stimulating the tibialis nerves to produce a displacement, the delay until the counterbalancing EMG activity started (about 40 ms) was in the time range of a fast-conducting segmental reflex. After partial ischaemic blocking of group I afferents from the leg muscles or fixation of the ankle joints, the predominant sway frequency was lacking, bursts of EMG activity became longer and stronger, and body balance was more unstable. Altering the height of the seesaw showed that a threshold change in the ankle angle was the determining factor in the production of spinal stretch reflex activity for fast regulation of balance.
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  • 8
    ISSN: 1432-1106
    Keywords: Human posture ; Induced sway ; Visual stabilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Displacements of the center of foot pressure, the hip and the head were recorded in six subjects standing on a platform, sinusoidally tilting in pitch(anterior-posterior).Stimulusfrequenciesranged between 0.01 and 1 Hz. Stimulus amplitudes were 2, 4 and 6 °. With eyes open the displacements were minimal at 0.3 Hz. With eyes closed, however, induced sway was maximal at this frequency. The apparent lack of visual stabilization at the lowest frequency (0.01 Hz) might be attributed to a subthreshold velocity of the retinal image motion induced by the swaying body. A similar absence of visual stabilization at 1 Hz is assumed to indicate the limit of the working range of visual stabilization of posture. Independent of stimulus amplitude a phase lead of about 90 ° was found at 0.01 Hz. This decreased with increasing frequency up to a phase lag of 100 ° at the highest frequency (1 Hz). Head stabilization was generally more effective than hip stabilization. EMG recordings from the leg muscles suggest that with eyes closed the center of force is mainly stabilized by leg muscle activity, while with eyes open this stabilization is best, when vision allows for stabilization of body posture by intersegmental movements between head, trunk and legs.
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  • 9
    ISSN: 1432-1106
    Keywords: Posture ; Movement precuing ; Cerebellar disease ; Parkinson's disease ; Motor control ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Automatic postural responses of leg muscles to the sudden displacement of standing support were investigated under four different conditions of information given to subjects in advance. Results from three groups of subjects were compared: 6 normal subjects, 10 patients with cerebellar disease, and 9 patients with Parkinson's disease. Specifically, each subject was provided with visual information about the direction and/or the amplitude of an upcoming platform tilt. For the control situation no advance information on the characteristics of platform tilt was provided. Neither the latencies nor the integrals of postural EMG-responses showed alterations with advance information. In contrast, in a control experiment in which 3 normal subjects had to perform large or small forward or backward voluntary movements of the body around the ankle joint, shorter onset-latencies of leg muscle EMG responses were observed with increasing complexity of the advance information. These results suggest that, unlike voluntary movements, postural responses to rapid surface tilts do not benefit from advance visual information on direction or amplitude of a postural disturbance.
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  • 10
    ISSN: 1432-1106
    Keywords: Saccadic eye movement ; Vestibular nerve ; Efferent fibres ; Saccadic modulation ; Tonic modulation ; Goldfish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Deutsche Zusammenfassung Bei Goldfischen wurden Einzelfaserimpulse im N. vestibularis registriert die vom rostralen linken Vestibularisnerven, vom isolierten linken Ramus ampullaris lateralis und vom proximalen Stumpf des durchgetrennten Nerven abgeleitet wurden. Von insgesamt 420 registrierten Vestibularis-Axonen zeigten 44 charakteristische Modulation der Spontanaktivität vor und bei raschen Augenbewegungen (Saccaden und rasche Phasen des periodischen Spontannystagmus). Die durch Augenbewegungen modulierten Neurone ließen sich in 4 Typen einteilen: 1. Der bidirektional aktivierte Typ a wurde jeweils mit der raschen Phase sowohl bei Links-, als auch bei Rechtsnystagmus aktiviert. 2. Der bidirektional gehemmte Typ i wurde bei raschen Nystagmusphasen in beiden Richtungen gehemmt. 3. Richtungsspezifische Neurone des Typ d, wurden bei raschen Phasen des Linksnystagmus gehemmt und bei Rechtsnystagmus aktiviert. 4. Stellungskorrelierte Neurone vom Typ p, deren Entladungsverhalten mit der Burbusstellung korreliert war. Bei Bulbusdeviation ipsilateral zur Elektrode waren sie tonisch aktiviert und bei Bulbusstellung kontralateral zur Elektrode gehemmt. Aktivierung und Hemmung begannen bei den Neuronentypen a, i und d stets vor der Sakkade. Es fanden sich Mischtypen zwischen den Neuronen a und p. Die Typen a, i und p fanden sich sowohl im intakten Nerven als auch im proximalen Stumpf des durchtrennten Nerven. Die seltenen richtungsspezifischen d-Neurone waren nur in intakten Nerven nachweisbar. Bei Neuronen aus den Makulaorganen (Utriculus, Sacculus und Lagena) ließ sich keine Beziehung zu Augenbewegungen beobachten. Zur Erklärung der Befunde werden Efferenzkollateralen von den supranucleären optomotorischen Zentren der Mittelhirn- und Brückenhaube angenommen, die in den Vestibularis projizieren. Die physiologische Bedeutung wird diskutiert.
    Notes: Summary Impulses of single fibres of the vestibular nerve in the goldfish were recorded either from the rostral portion of the left vestibular nerve, or from the left Ramus ampullaris lateralis, or from the proximal stump of the severed nerve. From a total of 420 registered neurons, 44 showed characteristic modulations of the spontaneous activity associated with any rapid eye movement. These neurons were divided into four types: 1. The bidirectionally activated type a was activated with fast phases of nystagmus both to the left and to the right. 2. The bidirectionally inhibited type i was inhibited with fast phases of nystagmus in both directions. 3. The directionally sensitive type d was inhibited during the rapid phase of nystagmus when its direction was ipsilateral and activated when its direction was contralateral to the side of the recording electrode. 4. The position sensitive type p was correlated with the position of the eyes. With deviation of the eye ipsilateral those neurons were tonically activated and with deviation of the eye contralateral to the side of the electrode, their activity was tonically reduced. Activation and inhibition in the type a, i, and d neurons always began before the saccade. In the type p neuron tonic frequency modulation dependent on eye position began up to 100 msec after a position change. Some neurons showed the characteristic behaviour of both type a and p neurons. These, as well as the pure type a, p and i neurons, were found in the intact nerve as well as in the proximal stump of the severed nerve. The rarer type d neurons were found only in the intact nerve. Neurons originating in the macula organs (Utriculus, Sacculus and Lagena) did not show frequency modulation with eye movements. Efferent modulations originating from supranuclear optomotor centers of the mesencephalic and pontine reticular formation were discussed in relation to their functional significance during combined eye and body movements.
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