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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Temporal coding of conspecific position in the hippocampus
No full textThe aim of this experiment was to determine whether the hippocampus formed a representation of the location of another animal. It was hypothesized that place cells in the hippocampus would encode spatial information regarding the location of a conspecific in an observation task where no movement planning was required of the observer. Four male Sprague Dawley rats (2 pairs) were used to examine these hypotheses. The pairs of rats were trained to shuttle in a box and were then habituated to an ‘observer box’. Single unit hippocampal data was collected from the observer both in the run condition (the observer itself shuttled backward and forward) and then in the watch condition (the observer was observing a conspecific shuttling). A small but significant correlation was observed between the place field locations in the run and watch conditions. In addition, significant theta phase precession occurred in the hippocampus based on the conspecific’s location. The hypotheses were supported and together the results suggested that the hippocampus encodes a social component of memory which has the ability to represent spatial location information of a conspecific. This representation could use both rate and temporal codes. These data suggest that the hippocampus could be a potential therapeutic target for disorders with impaired social function, such as schizophrenia
Hippocampal sharp wave ripple events and place cell activity in a ketamine model of schizophrenia
No full textThis experiment aimed to explore the role of hippocampal activity in a pharmacological model of schizophrenia, focusing on hippocampal place cell firing and associated sharp wave ripple events. In a within-subjects design, rats with tetrodes implanted in area CA1 of the hippocampus were administered either saline or a subanesthetic dose of ketamine across separate, three day sequences. Following injection, single cell and local field potential activity were recorded while the animals ran laps of a rectangular track for a reward, and again while they sat in a rest box. All animals completed both control and experimental sequences. In the control sequences, saline was administered on each of three consecutive days, while in the experimental sequences, the drug and control trials were alternated across consecutive days. Specifically, saline was administered on day one, ketamine on day two, and saline on day three. Results demonstrated that in both rest and run conditions, ketamine reduced the intrinsic frequency of sharp wave ripples, but did not alter any other ripple measures. None of the single cell measures were affected by ketamine administration in the rest nor run condition. Taken together, the results suggested that decreased sharp wave ripple frequency in the hippocampus may produce some of the schizophrenia-like symptoms observed in the ketamine model, but that the activity of individual place cells is not affected. The findings further support the glutamate theory of schizophrenia, as well as the role of the hippocampus in producing symptoms of the disorder
Variations on the Author
Get PDF“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
Get PDFWe 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
Fluoxetine treatment and its effect on the behaviour of MIA rats
No full textPrenatal immune insults have been shown to increase the offspring’s risk of developing schizophrenia. Based on this knowledge, a maternal immune activation (MIA) rat model of the disorder has been developed, where pregnant dams are injected with Poly I:C, a viral mimetic. Chapter 1 provides an introduction to this and other topics covered in the following thesis.
In chapter 2 pre-pulse inhibition (PPI) testing is described. Contrary to previous studies, no significant overall group difference was seen as a result of prenatal treatment. There was, however, a trend was observed in the expected direction, showing MIA animals to have a decreased %PPI response in comparison to saline treated animals, with this difference proving significant at 80dB, a middle range pre-pulse amplitude, which have been shown to elucidate group differences most clearly.
After the completion of PPI testing, animals underwent four consecutive days of treatment with Saline or the specific serotonin reuptake inhibitor Fluoxetine (Flx). A four week delay was used after drug treatment as we were interested in the effect of a time delay that corresponds to the treatment lag observed with antidepressants. Three different memory tasks followed.
In chapter 3, performance on two different Novel Object Displacement Tasks, a task relying on object recognition and location memory, is described. The first variation involved exposing animals to an environment with four objects, and after a 3.5-4 hour delay re- exposing animals to the environment, where the position of two objects had been swapped. In the second variation a similar procedure was used, but the environment only contained two objects, with one object displaced before re-exposure. Unexpectedly, no effect of prenatal treatment was observed. There was, however, a significant effect of drug treatment, showing that Flx treated animals spent less time around displaced objects than controls, suggesting a decrement in object-place memory.
One of the cognitive symptoms observed in schizophrenia is decreased flexibility in several tasks, including reversal learning. Therefore, chapter 4 describes performance on a reversal Y-maze task. While no differences were seen among treatment groups during training, an effect of prenatal treatment became apparent during reversal learning. It was found that MIA animals required significantly more trials to reach reversal criterion than saline treated rats. This contrasts previous data which demonstrated that MIA animals were quicker to reach reversal criterion. It is discussed that a major difference in the current study to previous ones was reward valence, with the current experiment using appetitive and previous using aversive motivating. This suggests that differences may be due to deficits in reward processing. No significant main effect or interaction of Flx treatment was observed.
Lastly, chapter 5 is dedicated to discussing the experiments, their limitations and potential implications. The behavioural memory studies presented here hint at an interesting relationship between prenatal immune insults and Flx treatment with time delays before testing in consideration of antidepressant treatment lag. Further research in this area may have huge implications in our understanding of these topics and underlying brain mechanisms, which would have immense therapeutic value
Hippocampal sharp wave ripple events and place cell activity in a ketamine model of schizophrenia
No full textThis experiment aimed to explore the role of hippocampal activity in a pharmacological model of schizophrenia, focusing on hippocampal place cell firing and associated sharp wave ripple events. In a within-subjects design, rats with tetrodes implanted in area CA1 of the hippocampus were administered either saline or a subanesthetic dose of ketamine across separate, three day sequences. Following injection, single cell and local field potential activity were recorded while the animals ran laps of a rectangular track for a reward, and again while they sat in a rest box. All animals completed both control and experimental sequences. In the control sequences, saline was administered on each of three consecutive days, while in the experimental sequences, the drug and control trials were alternated across consecutive days. Specifically, saline was administered on day one, ketamine on day two, and saline on day three. Results demonstrated that in both rest and run conditions, ketamine reduced the intrinsic frequency of sharp wave ripples, but did not alter any other ripple measures. None of the single cell measures were affected by ketamine administration in the rest nor run condition. Taken together, the results suggested that decreased sharp wave ripple frequency in the hippocampus may produce some of the schizophrenia-like symptoms observed in the ketamine model, but that the activity of individual place cells is not affected. The findings further support the glutamate theory of schizophrenia, as well as the role of the hippocampus in producing symptoms of the disorder
Hippocampal Place Cells Dynamically Encode Value of Available Goals During Spatial Navigation
No full textThe hippocampus plays a role in spatial navigation, and place cells (cells that fire selectively for an animal’s location in an environment) are thought to provide an anatomical basis for a cognitive map (a map-like representation of space in the brain). Recently, however, place cells have been found to encode more complex aspects of navigation than simply place; including information about the location or presence of upcoming goals. The present experiments aimed to investigate the involvement of the hippocampus in representing the value of a goal (taking into account the size of the reward and the cost in obtaining it), and its contribution to navigation.
Place cells were recorded while rats chose between two goals of differing value, in a spatial decision-making task conducted in a figure-of-eight maze. The value of a goal to an animal was inferred based on the proportion of trials in which that goal was chosen. It was hypothesised that cells would fire differentially in the maze depending on the available rewards, and that cell activity would be modulated by the value of upcoming rewards. It was also hypothesised that place cells representing goal value would dynamically encode changes in value when reward sizes were altered, and that this may influence the animal’s future behaviour. Additionally, it was predicted that a subset of cells would fire “out-of-field”, prior to the animal reaching the reward location those cells represented, possibly indicating the mental projection of the animal to that location.
The results showed that when animals are presented with rewards of two different values, more place cells are involved in the representation of the reward of higher value to the animal, as measured by the number of cells with fields in that region, despite there being no difference in firing rate. In the maze’s central stem, many cells showed differential firing based on upcoming goal choice. Additionally, a number of cells showed out-of-field firing, firing differentially in a secondary field with regard to the animal’s next choice, and the goal that cell represented.
When reward size in each goal changed every twenty trials of the 100-trial session, animals’ behaviour changed quickly to accommodate new reward values, and mean firing rate in the central stem mirrored the pattern of behaviour. The firing rate in the first pass through the stem following a change of reward size, but before a change in behaviour, was strongly correlated with the subsequent distribution of behaviour, whereas the firing rate for the last pass of each block was not. These results support previous research suggesting that the hippocampus is briefly engaged during route planning, but is not needed during the execution of a determined route. They also show for the first time that place cells dynamically encode goal value during spatial navigation.
It is proposed that during spatial decision-making, value information, possibly originating from the prefrontal cortex, is transferred to the hippocampus, where it is incorporated into the spatial map of the environment, enabling the animal to most efficiently direct its behaviour
Hippocampal Place Cells Dynamically Encode Value of Available Goals During Spatial Navigation
No full textThe hippocampus plays a role in spatial navigation, and place cells (cells that fire selectively for an animal’s location in an environment) are thought to provide an anatomical basis for a cognitive map (a map-like representation of space in the brain). Recently, however, place cells have been found to encode more complex aspects of navigation than simply place; including information about the location or presence of upcoming goals. The present experiments aimed to investigate the involvement of the hippocampus in representing the value of a goal (taking into account the size of the reward and the cost in obtaining it), and its contribution to navigation.
Place cells were recorded while rats chose between two goals of differing value, in a spatial decision-making task conducted in a figure-of-eight maze. The value of a goal to an animal was inferred based on the proportion of trials in which that goal was chosen. It was hypothesised that cells would fire differentially in the maze depending on the available rewards, and that cell activity would be modulated by the value of upcoming rewards. It was also hypothesised that place cells representing goal value would dynamically encode changes in value when reward sizes were altered, and that this may influence the animal’s future behaviour. Additionally, it was predicted that a subset of cells would fire “out-of-field”, prior to the animal reaching the reward location those cells represented, possibly indicating the mental projection of the animal to that location.
The results showed that when animals are presented with rewards of two different values, more place cells are involved in the representation of the reward of higher value to the animal, as measured by the number of cells with fields in that region, despite there being no difference in firing rate. In the maze’s central stem, many cells showed differential firing based on upcoming goal choice. Additionally, a number of cells showed out-of-field firing, firing differentially in a secondary field with regard to the animal’s next choice, and the goal that cell represented.
When reward size in each goal changed every twenty trials of the 100-trial session, animals’ behaviour changed quickly to accommodate new reward values, and mean firing rate in the central stem mirrored the pattern of behaviour. The firing rate in the first pass through the stem following a change of reward size, but before a change in behaviour, was strongly correlated with the subsequent distribution of behaviour, whereas the firing rate for the last pass of each block was not. These results support previous research suggesting that the hippocampus is briefly engaged during route planning, but is not needed during the execution of a determined route. They also show for the first time that place cells dynamically encode goal value during spatial navigation.
It is proposed that during spatial decision-making, value information, possibly originating from the prefrontal cortex, is transferred to the hippocampus, where it is incorporated into the spatial map of the environment, enabling the animal to most efficiently direct its behaviour
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