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Biomedical subjects

A Straube

Publications and source records attributed to A Straube.

159 records · Page 9Linked to original sources
PubMed1988

Neuronal activity in the flocculus of the alert monkey during sinusoidal optokinetic stimulation.

1. Activity of single units was recorded in the flocculus of alert, behaving monkeys during sinusoidal optokinetic (0.02-5.0 Hz), constant velocity optokinetic, vestibular and visual-vestibular conflict stimulation. The maximal stimulus velocity for sinusoidal optokinetic stimulation at different frequencies was 40 deg/s or less (at frequencies above 1 Hz). For an amplitude series at 0.2 Hz, stimulus velocity was varied between +/- 10 to +/- 80 deg/s. In one trained monkey activity was also investigated during smooth pursuit eye movements and suppression of the vestibulo-ocular reflex by visual fixation (VOR-supp.). Only neurons which responded to 0.2 Hz (+/- 40 deg/s) optokinetic stimulation were included in the study. 2. The majority of neurons (44 out of 59) were type I Purkinje cells (PCs), which increased their simple spike activity during optokinetic cylinder rotation to the ipsilateral recording side. The responses during other, vestibular related, paradigms allowed all these neurons to be classified as so called 'gaze velocity' PCs. Three type II PCs were encountered, which responded similarly, but were only weakly modulated. 3. All type I PCs were modulated at frequencies of sinusoidal optokinetic stimulation between 0.05 and 2.5 Hz. PC's showed little or no modulation at 0.03 and 0.02 Hz. About half of the PC's still responded at 5.0 Hz. 4. Relative to eye velocity, the PC activity had a phase advance of about 30 deg between 0.1 and 2 Hz. It became larger at lower, and smaller at higher, frequencies. Eye velocity related sensitivity (imp/s/deg/s) was small at low stimulus frequencies and increased monotonically, on average from 0.16 at 0.02 Hz to 2.0 at 3.3 Hz. 5. Ten (out of 12) mossy fiber related input neurons were classified as visual neurons, since their activity could be related to the amount of retinal slip in all conditions. Neurons were clearly modulated at sinusoidal optokinetic stimulation up to 5 Hz. One input neuron, investigated during sinusoidal OKN, smooth pursuit eye movements, VOR and VOR-supp., behaved qualitatively like a 'gaze velocity' PC. The remaining input neuron encoded eye velocity at 0.2 Hz optokinetic, vestibular and visual-vestibular conflict stimulation. 6. The results show that during sinusoidal and constant velocity optokinetic stimulation 'gaze velocity' PC's do not encode eye velocity and/or eye acceleration. 7. The vestibular nuclei-flocculus complementary hypothesis (Waespe and Henn 1981) can explain PC responses to a large extent.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Influence of head or trunk oscillations on visually induced self-motion perception in humans.

The influence of concurrent head or trunk movements on optokinetically induced self-motion perception has been investigated by measuring circularvection (CV) latencies. Active head as well as passive trunk oscillation cause an increase in circularvection latency of about 50% as compared to latencies with the head and trunk stationary during full field optokinetic stimulation. The results point towards an intersensory inhibition of self-motion perception.

Adolescent↗
PubMed1987

Visual postural performance after loss of somatosensory and vestibular function.

Visual stabilisation of body sway in a patient with severe deficits of the vestibular system (due to gentamicin treatment) and the somatosensory system (due to polyneuropathy) was studied. With eyes open the patient was able to stand and walk slowly. With eyes closed he lost balance within one second. In order to optimise visual stabilisation he intuitively searched for nearby visual targets. His postural sway was recorded using posturography. His balance performance deteriorated significantly beyond a distance of 1 m between the eyes and the surrounding objects and with visual acuity below 0.3 (experimentally achieved with semitransparent plastic foils). With flicker illumination of decreasing frequencies of the visual surround he needed at least a visual input rate of 17 Hz in order to maintain an upright body position. The data provide clinical evidence for rapid visuo-spinal control of posture.

Adult↗
PubMed1987

Paroxysmal spontaneous nystagmus and vertigo evoked by lateral eye position.

Prolonged lateral eye position to the extreme left for 5 to 20 seconds, without vestibular stimulation, induced intense attacks of nystagmus and rotational vertigo lasting 50-90 seconds in a patient. During the attacks the nystagmus beat to the right and counterclockwise, while the patient could look freely around. Clinical data were suggestive of repeated strokes in the vertebrobasilar territory, mainly affecting the right dorsolateral medulla oblongata including the vestibular nuclei. A paroxysmal attack of nystagmus and vertigo evoked by voluntary lateral eye position is an unusual clinical finding. This is discussed in the light of multisensory integration within the vestibular system, which also includes eye position information.

Brain↗
PubMed1987

Importance of the visual and vestibular cortex for self-motion perception in man (circularvection).

Circularvection (CV), the optokinetically induced perception of self-motion, is based neurophysiologically upon visual-vestibular convergence. It is yet not known which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system in order to make possible the convergence that has been found: the vestibular nuclei, the thalamus and the vestibular cortex. The functional significance of the visual cortex was demonstrated in 12 patients with homonymous hemianopia who neither perceived CV nor exhibited a postural destabilization when exposed to optokinetic pattern motion (yaw or roll) restricted to the scotoma. The functional significance of the vestibular cortex as well as ipsilateral visual-vestibular interaction was demonstrated in 4 (out of 20) patients with tumour lesions involving the vestibular cortex areas. They either failed to perceive CV or showed a significant increase of CV-latencies when monocular optokinetic stimulation was restricted to the ipsilateral visual cortex. Arguments for and against the following hypothesis are discussed: circularvection is induced by visual motion stimulation of the primary visual cortex which then activates vestibular nuclei neurons by descending pathways and which also informs the vestibular cortex that self-motion with a perceptual direction is involved. Determination of the velocity of CV is mediated by direct visual-vestibular cortex interaction, which most probably is also involved in the perceptual interpretation of motion perception: Self-motion versus object-motion.

Adult↗
PubMed1987

Importance of the visual cortex for postural stabilization: inferences from pigeon and frog data.

Optokinetically induced self-motion with its consequences for postural balance is based upon visual-vestibular convergence. It is a matter for speculation which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system. The functional significance of the visual cortex was tested by a behavioral approach in two animals, selected for their different evolutionary stage: frog (midbrain visual center); pigeon (primitive neocortical center). Lateral postural sway during optokinetic stimulation in roll served as a measurement for induced rollvection and apparent body tilt. Roll motion elicits a tonic 'compensatory' postural adjustment towards the direction of pattern motion in pigeon as in man but not in frog. From the lack of this reaction we infer that the frog does not perceive rollvection because it has no visual cortex. This agrees with the absence of visual-vestibular convergence in the frogs vestibular nuclei neurons as well as the absence of a nystagmus velocity storage in the brainstem. The animal experiments fit human data in hemianopic patients who also only experience rollvection when stimulated in the unaffected hemifield.

Animals↗
PubMed1985

Differential effects of ambivalent visual-vestibular-somatosensory stimulation on the perception of self-motion.

The direction of perceived self-motion was determined as a function of combined visual-vestibular and vestibulo-somatosensory stimulations about the earth's vertical z-axis by means of a rotary chair and drum system. The predominant influence of concurrent antagonistic vestibular stimulation on circular vection (CV) even at small accelerations has been demonstrated by several studies in the past. The results of the present paper do not confirm the generally assumed influence of the vestibular system on exocentric motion perception, but instead produce evidence of the dominance of the visual channel even at high acceleration levels. Using a joystick to indicate perceived self-motion, we found the following: Constant CV (visual stimulus velocity: 40 degrees/s) could only be cancelled by vestibular stimulations at oppositely directed mean angular accelerations of 26.9 +/- 9.1 degrees/s2. Smaller accelerations led merely to an acceleration level-related decrease in the perceived velocity of CV. Despite a clear decision with respect to the direction of the perceived motion, subjects (Ss) reported dizziness or even strong motion sickness symptoms. Similar results were obtained with vestibulo-somatosensory interactions. The results are interpreted in terms of an intensive visual support in the processing of visual-vestibular signals, particularly at cortical level, assuming a cortical velocity generator (CVG).

Adolescent↗
PubMed1985

[Nuclear magnetic resonance tomography and computed tomography of the brain for detection of Wilson's disease].

The authors report on two woman patients with confirmed Wilson's disease (hepatolenticular degeneration) who had neurological deficits and showed typical changes evident from laboratory data. Both computed tomography and magnetic resonance tomography revealed degenerative changes in the basal ganglia, especially of the lenticular nucleus, MR showing these defects more clearly than CT. There was a noticeable symmetrical enhancement of signals in the lenticular nucleus which was particularly evident on the image basing on the T2 (spin-spin relaxation time constant) values. MR could be superior to CT with regard to showing up pathological changes in the basal ganglia. The future indication of MR could be the establishment of an exact correlation between clinical signs and symptoms on the one hand, and morphological findings on the other. Over and above this, it should be explored to what extent MR can already detect degenerative changes in the brain in primarily hepatic types of the disease even without prior neurological examination.

Adult↗
PubMed1984

Visual stabilization of posture. Physiological stimulus characteristics and clinical aspects.

Visual stabilization of posture is critically dependent on stimulus characteristics as well as on the performance of the visual system. The purpose of the present investigation was to obtain quantitative data in man by means of posturography of fore-aft and lateral body sway in relation to different visual stimulus characteristics. Visual acuity, when decreased logarithmically, causes a linearly increasing postural instability, twice as prominent for fore-aft than for lateral sway. Any measurable visual contribution for fore-aft sway ceases with an acuity lower than 0.03 and for lateral sway with an acuity lower than 0.01. The central area of the visual field as compared with the peripheral retina dominates postural control. The foveal region exhibits a powerful contribution, in particular for lateral sway. A partial but significant visual stabilization is preserved with a visual input rate between 1 to 4 Hz flicker frequency. As soon as continuous motion perception becomes involved with frequencies higher than 4 Hz, visual stabilization gradually improves with a saturation at frequencies higher than 16 Hz. Lateral body sway activity and eye-object distance are linearly related: body sway decreases with increasing distance corresponding to the linear decrease of net retinal displacement with increasing eye-object distance. Aspects of 'afferent' and 'efferent' visual motion perception, which involve fore-aft and lateral body sway differently, are evaluated. The clinical relevance is demonstrated in patients with oculomotor disturbances. The results are discussed with respect to the variety of related clinical disorders, which involve reduction in visual acuity, field defects, accommodation disturbances and ocular oscillations.

Accommodation, Ocular↗
PubMedDate not supplied

[Spatial orientation and postural regulation in patients with idiopathic scoliosis].

QUESTION: Etiology of idiopathic scoliosis is unknown. In literature a primarily neurogenic disturbance of postural regulation is discussed with subsequent changes of the spine. In the present paper, individual functions of postural regulation in patients with idiopathic scoliosis were examined by neurophysiologic investigations and compared to a normal population. METHOD: The body sway of 28 patients was investigated in upright position under various testing conditions by means of a force measuring platform, allowing examination of the efferent part of postural regulation as well as the sensory systems involved. Registration of the eye movements (ENG) made it possible to investigate the function of the vestibulo-cerebellar system. Furthermore the optokinetic capability of scoliotic patients was tested by determination of the subjective visual vertical (SVV). RESULTS: It turned out that none of the neurophysiologic test procedures showed clearly pathological findings in scoliotic patients as compared to a normal population. CONCLUSION: It has not to be considered as probable that idiopathic scoliosis is caused by a disturbance of postural regulation.

Adolescent↗
PubMedDate not supplied

Intraprocedural thrombus formation during coil placement in ruptured intracranial aneurysms: treatment with systemic application of the glycoprotein IIb/IIIa antagonist tirofiban.

BACKGROUND AND PURPOSE: When using detachable coils to treat intracranial aneurysms, thromboembolism is the most feared and frequently reported complication during or after endovascular therapy. The purpose of this study was to document the therapeutic effect of tirofiban on patency of the parent vessel, rate of rebleedings, and outcome of the patients in the setting of acute subarachnoidal hemorrhage. METHODS: A patient data base was retrospectively reviewed to identify patients in whom thrombus occurred during endovascular treatment of ruptured cerebral aneurysms within a 34-month period and who were treated with tirofiban. All patients underwent anticoagulation with heparin during endovascular treatment procedures. Sixteen patients (age range, 52.9 +/- 10.7 years; 10 women, 6 men) were identified with intraprocedural thrombus formation. The patency of the parent vessel was assessed in a retrospective analysis blinded to outcome. Eight patients received ventriculostomy and had a follow-up CT. RESULTS: Local nonocclusive thrombus at the coil surface was detected in 5 patients, in all of whom the thrombus was dissolved. In 10 patients, partial or total occlusion of the parent vessel occurred during the intervention; in 8 of these, the vessel was recanalized completely and in 2 drug administration was assisted by mechanical means. In 1 patient, however, the occlusion persisted. No periprocedural rebleedings of the ruptured aneurysm occurred; 3 of 8 ventriculostomies had clinically silent small local bleedings. CONCLUSION: The use of tirofiban in the setting of endovascular treatment of ruptured intracranial aneurysms to dissolve platelet aggregation seems relatively safe and effective.

Adult↗
PubMedDate not supplied

Repeated single fiber recordings do not affect the jitter and the fiber density.

The temporal variation of at least two muscle fibers of the same motor unit was recorded with the single fiber EMG technique (SFEMG) by means of special needles and filter settings. In the normal musculus extensor digitorum communis (EDC) the mean variation (jitter) is not longer than 37 microseconds, the fiber density not higher than 1.7 fibers in a 10 ms window. To determine whether these parameters are affected by repeated SFEMG recordings, we measured jitter and fiber density in 20 fiber pairs in the left extensor digitorum communis muscle on day 0, 3, 6, 9 and 30 in 5 healthy volunteers. The mean jitter and the fiber density did not change significantly from day 0 (30.1 +/- 3.6 microseconds; 1.4 +/- 0.07) to day 30 (34.5 +/- 2.7 microseconds; 1.6 +/- 0.13). We conclude that repeated SFEMG recordings do not influence jitter and fiber density.

Adult↗
PubMedDate not supplied

Saccadic dysmetria is similar in patients with a lateral medullary lesion and in monkeys with a lesion of the deep cerebellar nucleus.

Some of the clinical hallmarks of lateral medullary infarction--Wallenberg's syndrome--are saccadic dysmetria, smooth pursuit deficit, and lateropulsion of the body. Similar movement disorders are seen in monkeys after local unilateral injection of GABAergic drugs in the caudal fastigial nucleus of monkeys. These include an ipsilateral saccadic hypermetria and a contralateral saccadic hypometria as well as cogwheel smooth pursuit eye movements toward the contralateral side and an ipsiversive lateropulsion of the body. It was previously suggested that the lateral medullary infarction causes a lesion of climbing fibers to the cerebellum. This lack of climbing fiber input increases the activity of ipsilateral Purkinje cells, which consequently provide too much inhibition of the deep cerebellar nuclei.

Adult↗