1,720,962 research outputs found
Generating functional for the gravitational field: implementation of an evolutionary quantum dynamics
No full textDynamics of decision‐related activity in hippocampus
No full textPlace-selective activity in hippocampal neurons can be modulated by the trajectory that will be taken in the immediate future (“prospective coding”), information that could be useful in neural processes elaborating choices in route planning. To determine if and how hippocampal prospective neurons participate in decision making, we measured the time course of the evolution of prospective activity by recording place responses in rats performing a T-maze alternation task. After five or seven alternation trials, the routine was unpredictably interrupted by a photodetector-triggered visual cue as the rat crossed the middle of central arm, signaling it to suddenly change its intended choice. Comparison of the delays between light cue presentation and the onset of prospective activity for neurons with firing fields at various locations after the trigger point revealed a 420 ms processing delay. This surprisingly long delay indicates that prospective activity in the hippocampus appears much too late to generate planning or decision signals. This provides yet another example of a prominent brain activity that is unlikely to play a functional role in the cognitive function that it appears to represent (planning future trajectories). Nonetheless, the hippocampus may provide other contextual information to areas active at the earliest stages of selecting future paths, which would then return signals that help establish hippocampal prospective activity. © 2012 Wiley Periodicals, Inc
Dynamics of decision-related activity in prospective hippocampal place cells
No full textThe hippocampus is involved in
spatial navigation and contextual memory. Hippocampal principal cells fire
when a rat is in a specific place in its environment and this place cell activity
can be prospectively modulated by the rat’s imminent trajectory. Here we
examined whether there is a link between prospective coding and navigational
decision processing.
We recorded place cells in rats performing a task involving a sudden decisional
switch and assessed the latency of the prospective activity onset. Rats learned
to alternate (ALT) in a continuous T-maze task. Every 5 to 7 trials, a visual cue
(VC) was presented as the rat crossed a photodetector at the middle of the
central arm. This instructed the rat to repeat a visit to the previous arm rather
than to continue alternating. Prospective activity was assessed with a bootstrap
method yielding fine grained spatial resolution of differences in spike rate
functions between leftward and rightward trajectories (controlling for
differences in lateral position along the leftward vs rightward trajectories). This
method allowed us to precisely determine where place cell responses started to
change after presentation of the VC relative to ALT trials.
We recorded 816 cells in 4 rats in 26 sessions. Of these, 19 neurons had
prospective activity in the central arm. In 15 out of 19 cells the onset of
significant prospective activity occurred further down the arm in cued trials
than in alternation trials. Consistent with our hypothesis that prospective
activity was triggered after a fixed time T following the cue presentation, this
difference was greater for cells with place fields closer to the photodetector. A
linear regression (t-test for significant slope p=0.0128) of the onset times of
activity in ALT trials plotted as a function of the time difference between the
activity onsets of VC and ALT trials yielded a value of T ~ 450ms.
This relatively long delay for prospective activity to arise (compared, e.g., to 150 ms after cue presentation for orienting decision signals in the superior
colliculus; Felsen & Mainen, 2008, Neuron, 60:137) suggests that there is
substantial pre-processing before this information reaches the hippocampus,
perhaps in pathways involving cortico-striatal loops. Thus the navigational
behavioral choice signal is likely elaborated elsewhere, then transmitted to the
hippocampus to inform prospective activity. The hippocampus would then
engage this for contextual processing of memories in time and space. Recording
in other areas with this type of paradigm should permit detection of the earliest
appearances of navigational choice related activity
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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