1,720,967 research outputs found
Role of the cortico-basal ganglia loops in visual attention: effects of dopaminergic and subthalamic nucleus stimulation in Parkinson's disease
No full textLo scopo di questo studio è stato quello di valutare il possibile ruolo dei diversi circuiti cortico-sottocorticali passanti per i gangli della base e della via dopaminergica sui meccanismi di top-down e bottom-up dell’attenzione visiva (AV).
A tal fine, abbiamo confrontato le prestazioni in 3 paradigmi computerizzati, adatti a studiare la cattura attenzionale (AC), la selezione della risposta motoria, e l’avvio del movimento, di due gruppi di pazienti affetti da malattia di parkinson (MP) - uno valutato in differenti condizioni di stimolazione elettrica (senza stimolazione, con stimolazione selettiva dell’area sensorimotoria, SM, o di quella associativa, AS, del nucleo subtalamico, NST), l’altro in differenti condizioni terapeutiche (con o senza trattamento dopaminergico) - con quelle di un gruppo di soggetti di controllo.
I nostri risultati hanno evidenziato che nella MP vi è un indebolimento dei meccanismi top-down di controllo dell’AV, che può spiegare, indirettamente, il parallelo incremento dell’AC osservato nelle medesime condizioni. Il trattamento dopaminergico si è dimostrato efficace nel ricondurre alla normalità i meccanismi top-down dell’AV, suggerendo un coinvolgimento della via dopaminergica in questa funzione della sfera cognitiva. Questa via sembra giocare un ruolo anche nei meccaniesmi di bottom-up dell’attenzione, come suggerito dall’aumento della CA osservato per effetto del trattamento dopaminergico.
La stimolazione del NST ha evidenziato un quadro simile a quello ottenuto con il trattamento dopaminergico, indicando un coinvolgimento diretto dei gangli della base nel controllo dell’AV. In particolare, i nostri risultati evidenziano una specializzazione funzionale dei differenti sub-territori del NST, nei meccanismi top-down. La stimolazione dell’area SM ha degli effetti pronunciati sui meccanismi d’avvio del movimento e un effetto positivo sui meccanismi dell’AVE, mentre la stimolazione AS sembra essere efficace soprattutto sui meccanismi di selezione del target.We aimed to investigate the possible role of cortico-basal ganglia loops and dopaminergic pathways in the mechanisms of top-down and bottom-up control of visual attention (VA).
We compared the performances on 3 computerized tasks, respectively suitable to study attentional capture (AC), motor response selection and movement initiation, of two groups of patients with Parkinson’s disease (PD), one evaluated in different sets of electrical stimulation (without stimulation, or selective stimulation of the sensorimotor, SM, or associative, AS, parts of the subthalamic nucleus, STN), the other in different conditions of medication (with or without levodopa), with those of a group of controls.
Our results showed that in PD there is a weakening of the mechanisms underlying the top-down control of VA, which also would account indirectly account for the enhancement of AC. Dopaminergic treatment proved to be effective in restoring the top-down mechanisms of VA, suggesting an involvement of dopaminergic pathways in this cognitive domain. These pathways seem to play a role also in the bottom-up mechanisms of attention, as suggested by the enhancement of AC under dopaminergic treatment.
The STN-stimulation showed a similar effect to that obtained by dopaminergic treatment, establishing a direct involvement of the basal ganglia loops in VA control. Our results highlighted a functional specialization of different sub-territories of the STN in relation to the top-down mechanisms. SM stimulation produced marked effects on the movement initiation processes and appreciable positive effects on endogenous VA mechanisms, while AS stimulation seems to be especially effective in improving the mechanisms of target selection
Effects of variyng subthalamic nucleus stimulation on apraxia of lid opening in Parkinson's disease.
No full textApraxia of lid opening (ALO) is a non-paralytic
inability to open the eyes or sustain lid elevation at
will. The exact pathophysiological mechanisms underlying
the syndrome are still unknown. ALO has been reported in
patients with Parkinson’s disease (PD) after subthalamic
nucleus (STN) deep brain stimulation (DBS), suggesting a
possible involvement of the basal ganglia. We aimed to
assess the effects of varying STN stimulation voltage on
ALO in PD patients. Seven out of 14 PD patients with
bilateral STN stimulation consecutively seen in our centre
presented with ALO. We progressively increased voltage
on each STN, using either 130 Hz (high-frequency stimulation,
HFS) or 2 or 3 Hz (low-frequency stimulation,
LFS). In five patients, HFS induced ALO time-locked to
stimulation in 7 out of 10 STNs at a voltage higher than
that used for chronic stimulation. LFS induced myoclonus
in the pretarsal orbicularis oculi muscle (pOOm) with a
rhythm synchronous to the frequency. In the other two
patients with ALO already present at the time of the stud
Focal motor seizures mimicking hemifacial spasm
No full textA young female patient, who presented acutely with an unusual movement disorder characterized by hyperkinetic facial movements, was referred to us for hemifacial spasm. The only abnormality on neurological examination was myoclonus of the left perioral and bilateral periorbital muscles, exacerbated by mental tasks. A week later, the patient also presented two generalized tonic-clonic seizures on awakening and was successfully treated with antiepileptic drugs. Laboratory and neuroimaging investigations yielded normal findings. Although we were unable to identify a cortical generator, the concomitant occurrence of generalized seizures, the disappearance of symptoms after treatment and the topography of the myoclonus support an epileptic origin of this myoclonus
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
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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