1,720,957 research outputs found
The influence of temporary blockage of semicircular canals on the loss and recovery of vestibuloocular reflexes
No full textThe efficacy of the technique of semicircular canal plugging in selectively blocking the function of individual semicircular canals was evaluated in rabbits. The horizontal and vertical vestibuloocular reflexes (HVOR, VVOR) and the horizontal optokinetic reflex (HOKR) were measured before the horizontal or anterior semicircular canals (HSCs, ASCs) were plugged bilaterally with small spindles of silver wire. These reflexes were also measured after the plugs were removed. The gain of the HVOR was reduced to less than 0.05 at all frequencies tested after plugs were inserted into the HSCs. The gain of the HOKR was not influenced by the plugging operation. These data were interpreted to mean that the plugs blocked the normal fluid dynamics of the HSCs, but did not alter the spontaneous activity of HSC afferents. The gain of the VVOR was not reduced by plugs of the HSCs. The gain of the VVOR was reduced by plugs of the ASCs. The residual VVOR was attributed to stimulation of the utricular otoliths at lower frequencies and stimulation of the posterior semicircular canals at higher frequencies. The gain of the HVOR was reduced 10–40% by plugs of the ASCs. These data, in conjunction with the presence of a small residual gain of the HVOR following bilateral plugs of the HSCs, suggest that the ASCs contribute to the HVOR. The gains of the HVOR and VVOR recovered to within 88% of the preplug values once the plugs of the HSCs or ASCs were removed. However, the protracted time course of this recovery, 10–15 d, indicated that the plugging operation, although reversible, does cause some temporary damage to the peripheral labyrinth.</jats:p
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
The induction and compensation of asymmetric eye movements following unilateral blockage of a horizontal semicircular canal in the rabbit
No full textThe influence of unilateral plugs of the left horizontal semicircular canal (LHC plugs) of rabbits on the development and compensation of asymmetric eye movements evoked by horizontal vestibular stimulation was studied. LHC plugs caused an immediate reduction of 50–65% in the gain of the horizontal vestibuloocular reflex (HVOR). This reduction in gain was achieved without altering the symmetry of the HVOR, and was accompanied by a change in the axial alignment of eye movements evoked by vestibular stimulation about the vertical (HVOR) and longitudinal (VVOR) axes. Postoperative asymmetry of eye movements developed 12–48 hr after the plugging operation. The development of asymmetry was reduced if the rabbit was restrained for 24 hr, thereby minimizing vestibular stimulation following the plugging operation. Over a 3–4 week period, the normal symmetry of eye movements was restored and the axial alignments of the HVOR and VVOR returned to the preoperative values. The gain of the HVOR did not recover. The horizontal cervicoocular reflex (HCOR) was examined before the plugging operation and after compensation of asymmetry was complete. The gain and phase of the HCOR were not altered. A relatively simple set of explanations at a cellular level is proposed to account for the induction and compensation of asymmetric eye movements following a unilateral plug of the horizontal semicircular canal.</jats:p
Optokinetic stimulation increases corticotropin-releasing factor mRNA in inferior olivary neurons of rabbits
No full textStimulus-specific changes in levels of corticotropin-releasing factor (CRF) mRNA in inferior olivary neurons were studied in unanesthetized rabbits. The possible functional importance of CRF, a neuropeptide that is expressed in all inferior olivary neurons, in cerebellar synaptic transmission was investigated in a subpopulation of inferior olivary neurons, the caudal dorsal cap. Previous studies have shown that unidirectional, binocular optokinetic stimulation increases the level of discharge in neurons located in one of the caudal dorsal caps of the inferior olive and decreases the level of discharge in neurons in the opposite dorsal cap. We investigated the influence of prolonged (1–144 hr), unidirectional, binocular, optokinetic stimulus on the levels of CRF mRNA in dorsal cap neurons, measured with the technique of hybridization histochemistry. Rabbits were placed at the center of a cylindrical optokinetic drum that rotated at a constant velocity of 5 deg/sec, stimulating one eye in the posterior-to-anterior direction and the contralateral eye in the anterior-to-posterior direction. Posterior- to-anterior stimulation of the left eye evoked increased activity of inferior olivary neurons located in the right caudal dorsal cap. Conversely, anterior-to-posterior stimulation of the right eye evoked decreased activity of neurons in the left caudal dorsal cap. The levels of CRF mRNA in dorsal cap neurons that were activated by prolonged optokinetic stimulation were increased by a factor of 4 to 7 after 48 hr of stimulation and by more than a factor of 10 after 144 hr of optokinetic stimulation. These optokinetically induced increases in CRF mRNA decayed to background levels after 30 hr. Our observations implicate CRF in visual olivocerebellar function and suggest that CRF may play a role in the plastic control of eye movement mediated by the visual olivocerebellar system.</jats:p
Optokinetically evoked expression of corticotropin-releasing factor in inferior olivary neurons of rabbits
No full textThe otolithic origin of the vertical vestibuloocular reflex following bilateral blockage of the vertical semicircular canals in the rabbit
No full textThe influence of bilateral plugs of the anterior and posterior semicircular canals (ASCs, PSCs) on the vertical vestibuloocular reflex (VVOR-0) of the rabbit, oscillated about the longitudinal axis maintained in a horizontal orientation, was studied. Bilateral plugs of either the ASCs or PSCs reduced the gain of the VVOR-0 evoked by stimulus frequencies above 0.005 Hz, but left a residual gain of the VVOR at higher stimulus frequencies that could be attributed to the remaining vertical canals and utricular otoliths. Bilateral plugs of both the ASCs and PSCs totally eliminated the canal component of the VVOR-0, as determined from measurements made when the animal was oriented at 90 degrees (“nose up”) with respect to the earth horizontal axis, eliminating changes in the gravitational vector acting on the utricular maculae (VVOR-90). Bilateral plugs of both the ASCs and PSCs also eliminated the nonlinear increase in gain observed at intermediate frequencies in intact rabbits when oscillated about a supine orientation (VVOR-180). The contribution of the utricular otolith to the VVOR-0 in rabbits with both the ASCs and PSCs plugged was compared with the predicted otolith contribution based on the assumption of linear summation of semicircular canal and utricular signals. The assumption of linear summation appears to be incorrect. Bilateral plugs of the ASCs and PSCs increased the latency and the time constant of vertical eye movements evoked by step-roll stimulation about the longitudinal axis maintained in a horizontal orientation.</jats:p
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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