1,720,977 research outputs found
Role of Intrinsic Burst Firing, Potassium Accumulation, and Electrical Coupling in the Elevated Potassium Model of Hippocampal Epilepsy
No full text Jensen, Morten S. and Yoel Yaari. Role of intrinsic burst firing, potassium accumulation, and electrical coupling in the elevated potassium model of hippocampal epilepsy. J. Neurophysiol. 77: 1224–1233, 1997. Perfusing rat hippocampal slices with high-K+ (7.5 mM) saline induced brief population bursts originating in CA3 at 0.5–1 Hz and spreading synaptically into CA1. In 42% of the slices the brief bursts evoked in CA1 gave way every 0.5–2 s to sustained ictal (or seizure) episodes with tonic and clonic components. Paired intra- and extracellular recordings in the CA1 pyramidal layer were used to characterize the synaptic and nonsynaptic mechanisms generating the brief and sustained epileptiform events. The interictal, tonic, or clonic primary burst response in CA1 comprised a spindle-shaped, tight cluster (170–180 Hz) of five to seven population spikes. Bursts evoked between sequential seizures (interictal bursts) were initially small and progressively increased in size. Concurrently, basal extracellular K+ concentration ([K+]o) increased from 6.5 to 7.5 mM. The tonic event emanated from a large primary burst and comprised prolonged (>1 s), self-sustained afterdischarge, associated with a rise in [K+]o to 12 mM. Bursts generated during the subsequent [K+]o decline (clonic bursts) also were large and followed by some afterdischarge. They became small during [K+]o undershoot to 6.5 mM. Intrinsically burst firing pyramidal cells (PCs) were recruited before or at the very onset of the primary population burst and fired repetitively during its course. Nonbursters were recruited ≥10 ms after the beginning of the primary burst and fired, on average, only one spike. The PCs depolarized during the primary burst and subsequent afterdischarge. The primary depolarizing shift was larger in bursters than in nonbursters. Both bursters and nonbursters fired repetitively, albeit intermittently, during tonic and clonic afterdischarge. Throughout the interictal-ictal cycle intracellular spikes were time-locked to population spikes, indicating that PCs fire in tight synchrony. Differential recording of transmembrane potentials unmasked rapid (4–7 ms) transmembrane depolarizing potentials of up to 10 mV, coincident with population spikes. We conclude that in the high-K+ model of hippocampal epilepsy, the local generation of population bursts in CA1 is led by intrinsic bursters, which recruit and synchronize other PCs by synaptic, electrical, and K+-mediated excitatory interactions. The cycling between interictal, tonic, and clonic events appears to result from feedback interactions between neuronal discharge and [K+]o. </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
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
Persistent Na+ and M-type K+ currents opposingly control spike gain in CA3 pyramidal cells
No full textNeural firing response gain and spike threshold are critical intrinsic cell properties that define input-output relations in neurons. Alterations of these cellular properties in hippocampal pyramidal cells (PCs) may strongly influence network dynamics in health and disease. Here we investigated how specific voltage-gated conductance affect these properties in adult rat CA3 pyramidal cells (PCs) in hippocampal slices under near-physiological conditions. We examined currents activated at near-threshold potential – persistent sodium current (INAP), T-type Ca2+ current (ICaT), M-type K+ current (IM), SK Ca2+ − dependent current (ISK), and h-type cationic current (Ih) through pharmacological modulation and analysis of resulting changes. CA3 PCs showed high heterogeneity in firing response gain, likely reflecting individual variations in active conductance at rest. Blocking INAP by riluzole decreased firing response gain, an effect associated with a reduction in the depolarizing shift (DS) underlying evoked spike trains. Conversely, blocking IM with XE991 markedly increased firing response gain, decreased the DS, increased input resistance, and lowered spike threshold. Enhancing IM by retigabine produced opposite effects. Blocking ISK with apamin moderately augmented firing response gain, while blocking ICaT and Ih exerted no effect on discharge.Our findings identify INaP and IM as key determinants of spike response gain and threshold of CA3 PCs, suggesting that modulators of these currents may effectively modify neuronal input-output relations in both normal and pathological states of hippocampal hypo- or hyperexcitability
Antiepileptogenesis, Plasticity of AED Targets, Drug Resistance, and Targeting the Immature Brain
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