1,720,995 research outputs found
Interaural Translational VOR: Suppression, Enhancement, and Cognitive Control
No full textWe investigated the influence of cognitive factors on the early response of the interaural translational vestibuloocular reflex (tVOR) in six normal subjects. Variables were prior knowledge of direction of head motion and the position of the fixation target relative to the head [head-fixed (HF) or space-fixed (SF)]. A manually driven device provided a step-like head translation (∼35 mm distance, peak acceleration, 0.6-1.3 g). Subjects looked at the SF or HF target located 15 cm in front of their heads in otherwise complete darkness. The testing paradigms were: random interleaving of SF and HF targets with unknown direction of head movement, known target location with random head direction (SFR or HFR), and known target location with known head direction (SFP or HFP). Timing was always unpredictable. A "gain" of the slow phase was calculated with respect to ideal performance (maintained fixation of the SF target, recorded/ideal eye velocity computed at time of peak head velocity). At such times, there were no significant differences in gain between HF and SF trials in the random condition; the average gain was ∼36% of ideal. On the other hand, responses in the SFR and HFR conditions differed as early as 20 ms after the head began moving. Average gain was higher (0.43 ± 0.11 vs. 0.34 ±0.14; means ± SD, P < 0.05) for each subject in the SFR than the HFR condition. For SFP and HFP, the responses differed from the onset of head motion. Average slow-phase gain was higher (0.49 ± 0.12 vs. 0.31 ± 0.12, P < 0.02) for each subject in SFP than in HFP. The timing of corrective saccades during the IVOR was also influenced by cognitive factors. Visual error signals seemed to be more important for triggering saccades in HF trials, whereas preprogramming, probably based on labyrinthine information, seemed to be more important in SF trials. Simulations showed that the changes in slow-phase gain with cognition could be reproduced with simple parametric adjustments of the gain of activity from otolith afferents and suggest that higher-level cognitive control of the VOR could occur as early as the synapse of peripheral afferents on neurons in the vestibular nuclei, either directly from higher level centers or via the cerebellum. In sum, the tVOR-both in its slow-phase response and the saccadic corrections-is subject to "higher-level" cognitive influences including knowledge of where the line of sight must point during head motion and the impending direction of head motion
Benign Paroxysmal Positional Vertigo: What We Do and Do Not Know
No full textBenign paroxysmal positional vertigo (BPPV) is common, sometimes terrifying, but rarely portends serious disease. It is usually easily diagnosed and treated, and both the patient and the physician are immediately gratified. While much has been learned about the pathogenesis of BPPV in the past decades, many of its features remain mysterious, and one must still be wary of the rare times it mimics a dangerous brain disorder. Here we review common, relatively well understood clinical features of BPPV but also emphasize what we do not know and when the physician must look deeper for a more ominous cause. © 2020 Georg Thieme Verlag. All rights reserved
Novel molecular mechanism of essential tremor: A computational approach.
No full textProgram No. 211.10 Abstract Viewer/Itinerary Planner. Onlin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ocular oscillations generated by coupling of brainstem excitatory and inhibitory saccadic burst neurons
No full textAbstract The human saccadic system is potentially
unstable and may oscillate if the burst neurons, which
generate saccades, are not inhibited by omnipause
neurons. A previous study showed that combined saccade
vergence movements can evoke oscillations in normal
subjects. We set out to determine: 1) whether similar
oscillations can be recorded during other paradigms
associated with inhibition of omnipause neurons; 2)
whether lesions of the fastigial nuclei disrupt such
oscillations; and 3) whether such oscillations can be
reproduced using a model based on the coupling of
excitatory and inhibitory burst neurons. We recorded
saccadic oscillations during vergence movements, combined
saccade-vergence movements, vertical saccades,
pure vergence and blinks in three normal subjects, and in a
patient with saccadic hypermetria due to a surgical lesion
affecting both fastigial nuclei. During combined saccadevergence,
normal subjects and the cerebellar patient
developed small-amplitude (0.1–0.5°), high-frequency
(27–35 Hz), conjugate horizontal saccadic oscillations.
Oscillations of a similar amplitude and frequency occurred
during blinks, pure vergence and vertical saccades. One
normal subject could generate saccadic oscillations
voluntarily (~0.7° amplitude, 25 Hz) during sustained
convergence. Previous models proposed that high-frequency
eye oscillations produced by the saccadic system
(saccadic oscillations), occur because of a delay in a
negative feedback loop around high-gain, excitatory burst
neurons in the brainstem. The feedback included the
cerebellar fastigial nuclei. We propose another model that
accounts for saccadic oscillations based on 1) coupling of
excitatory and inhibitory burst neurons in the brainstem
and 2) the hypothesis that burst neurons show postinhibitory
rebound discharge. When omnipause neurons
are inhibited (as during saccades, saccade-vergence movements
and blinks), this new model simulates oscillations
with amplitudes and frequencies comparable to those in
normal human subjects. The finding of saccadic oscillations
in the cerebellar patient is compatible with the new
model but not with the recent models including the
fastigial nuclei in the classic negative-feedback loop
model. Our model proposes a novel mechanism for
generating oscillations in the oculomotor system and
perhaps in other motor systems too
What clinical disorders tell us about the neural control of saccadic eye movements
No full textSaccades are rapid eye movements that redirect the fovea from one object to another. A great deal has been learned about the anatomy and physiology of saccades, making them an ideal system for studying the neural control of movement. Basic research on normal eye movements has greatly increased our understanding of saccadic performance, anatomy and physiology, and led to a large number of control system models. These models simulate normal saccades well, but are challenged by clinical disorders because they often do not incorporate the specific anatomical and physiological substrates needed to model clinically important abnormalities. Historically, studies of saccadic abnormalities in patients have played a critical role in understanding the neural control of saccades because they provide information that complements basic research and thus restricts hypotheses to those that are biologically plausible. This review presents four examples of clinical disorders (slow saccades, interrupted saccades, high-frequency saccadic oscillations and macrosaccadic oscillations) that have provided insights into the neurobiology of saccades, have driven the development of new models, and have suggested an explanation or treatment for these disorders. We raise general questions for both scientists and clinicians that will assist in their efforts to understand the neural control of movement, improve diagnostic criteria and develop new treatments
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Novel molecular mechanism of saccadic oscillations.
No full textProgram No. 819.15/Y21 2006 Abstract Viewer/Itinerary Planner, online
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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