1,972 research outputs found
Optimizing Associative Information Transfer within Content-addressable Memory
Original article can be found at: http://www.oldcitypublishing.com/IJUC/IJUC.htmlPeer reviewe
逆想起を用いた形態学的連想記憶モデルに関する研究
九州工業大学博士学位論文 学位記番号:生工博甲第241号 学位授与年月日:平成27年3月25日第1章 序論|第2章 連想記憶モデル|第3章 記銘パターンから独立した核パターンを用いたMAM|第4章 逆想起を用いたMAM|第5章 分割記銘により計算量を抑えた逆想起を用いたMAM|第6章 結論九州工業大学平成26年
Two computational neural models : rodent perirhinal cortex and crab cardiac ganglion
Neural engineering research has been rapidly growing in prominence in the past two decades, with 'reverse engineer the brain' listed as one of the 14 grand challenges outlined by the National Academy of Engineering. The computational aspect of reverse engineering includes a study of how both single neurons and networks of neurons integrate diverse signals from both the environment and from within the animal and make complex decisions. Since there are many limitations on the experiments that can be performed in alive or isolated biological systems, there is a need of standalone computational models which can help perform 'in silico' experiments. This dissertation focuses on such 'in silico' neuronal models to predict underlying mechanisms of governing interactions and robustness. The first model investigated is that of a rodent perirhinal cortex area 36 (PRC), and its role in associative memory formation. A large-scale 520 cell biophysical model of the PRC was developed using biological data from the literature. We then used the model to shed light on the mechanisms that support associative memory in the perirhinal network. These analyses revealed that perirhinal associative plasticity is critically dependent on a specific subset of neurons, termed conjunctive cells. When the model network was trained with spatially distributed but coincident neocortical inputs, these conjunctive cells acquired excitatory responses to the paired neocortical inputs and conveyed them to widely distributed perirhinal sites via longitudinal projections. Ablation of conjunctive cells during recall abolished expression of the associative memory. The second model focuses on a model for crab cardiac system consisting of five Large Cells (LC) developed using firsthand biological data. The model is then used to study the features of its underlying oscillation in its membrane potential during a rhythm and to reverse engineer the experimentally discovered phenomenon related to network synchrony. The model predicted multiple mechanisms of compensation to restore network synchrony based on compensatory intrinsic conductances. Finally, a third model, related to the second one, was of an improved three-compartmental biophysical model of an LC that is morphologically realistic and includes provision for inputs from the SCs. To determine viable LC models, maximal conductances in three compartments of an LC are determined by random sampling from a biologically characterized 9D-parameter space, followed by a three-stage rejection protocol that checks for conformity with features in experimental single cell traces. Random LC models that pass the single cell rejection protocol are then incorporated into a network model followed by a final rejection protocol stage. Using disparate experimental data, the study provides hitherto unknown structure-function insights related to the crustacean cardiac ganglion large cell, including the differential roles of active conductances in the three compartments. The novel morphological architecture for the large cell was validated using biological data and used to make predictions about function. A testable prediction related to function was that active conductances, specifically, the persistent sodium current, is required in the neurite to transmit the spike waveforms from the spike initiation zone to the soma. Another pertains to the co-variation of maximal conductances of the persistent sodium current with that of the leak current
The role of phonology in visual word recognition: evidence from Chinese
Posters - Letter/Word Processing V: abstract no. 5024The hypothesis of bidirectional coupling of orthography and phonology predicts that phonology plays a role in visual word recognition, as observed in the effects of feedforward and feedback spelling to sound consistency on lexical decision. However, because orthography and phonology are closely related in alphabetic languages (homophones in alphabetic languages are usually orthographically similar), it is difficult to exclude an influence of orthography on phonological effects in visual word recognition. Chinese languages contain many written homophones that are orthographically dissimilar, allowing a test of the claim that phonological effects can be independent of orthographic similarity. We report a study of visual word recognition in Chinese based on a mega-analysis of lexical decision performance with 500 characters. The results from multiple regression analyses, after controlling for orthographic frequency, stroke number, and radical frequency, showed main effects of feedforward and feedback consistency, as well as interactions between these variables and phonological frequency and number of homophones. Implications of these results for resonance models of visual word recognition are discussed.postprin
Behavioural Flexibility in Bumblebees (Bombus impatiens)
Foraging bumblebees (Bombus impatiens) extract nectar and pollen from a wide variety of morphologically distinct flower species, referred to as flower handling. Bumblebees learn this behaviour and acquisition of multiple flower handling techniques is a demonstration of behavioural flexibility. The purpose of this thesis is to understand how bumblebees are able to forage flexibly. This research has three specific goals: (1) to identify the cognitive mechanisms that support flower handling learning, (2) to understand how bumblebees avoid interference costs between multiple handling techniques, and (3) to explore the relation between behavioural flexibility and the mushroom bodies of the bumblebee brain. To address the first two goals, I developed a laboratory model of flower handling. The model consisted of a tube with a plastic door insert that bumblebees moved to access a nectar reward. The door was designed to be similar to a flower petal that a bee would lift to access a nectary in a real flower. All bees demonstrated the same set of motor behaviours and showed improvement across trials by increasing the frequency with which they used the successful behaviour. The apparatus was then adapted to measure bees’ ability to switch between two handling tasks, representing two different flower morphologies. Two variations of the apparatus were used, each of which required a different innate motor pattern for successful removal of the door. Bees switched between the two tasks by changing only the frequency that they engaged in each successful motor behaviour. The role of the mushroom bodies in behavioural flexibility was examined by training bees on a measure of behavioural flexibility, reversal learning, and relating performance to volume of the mushroom bodies and their components. Performance on the reversal task did not correlate with mushroom body volume. My overall findings are that bumblebees use a combination of innate motor patterns and learned associations to forage on a variety of flower species and the flexibility of individual bumblebees is not related to individual variation in volume of the mushroom bodies and their components
Interactive effects of orthography and semantics in Chinese picture naming
Posters - Language Production/Writing: abstract no. 4035Picture-naming performance in English and Dutch is enhanced by presentation of a word that is similar in form to the picture name. However, it is unclear whether facilitation has an orthographic or a phonological locus. We investigated the loci of the facilitation effect in Cantonese Chinese speakers by manipulating—at three SOAs (2100, 0, and 1100 msec)—semantic, orthographic, and phonological similarity. We identified an effect of orthographic facilitation that was independent of and larger than phonological facilitation across all SOAs. Semantic interference was also found at SOAs of 2100 and 0 msec. Critically, an interaction of semantics and orthography was observed at an SOA of 1100 msec. This interaction suggests that independent effects of orthographic facilitation on picture naming are located either at the level of semantic processing or at the lemma level and are not due to the activation of picture name segments at the level of phonological retrieval.postprin
Associative Recognition: Exploring the Contributions of Recollection and Familiarity
Episodic memory refers to the storage and retrieval of information about events in our past. According to dual process models, episodic memory is supported by familiarity which refers to the rapid and automatic sense of oldness about a previously encoded stimulus, and recollection which refers to the retrieval of contextual information, such as spatial, temporal or other contextual details that bring a specific item to mind. To be clear, familiarity is traditionally assumed to support recognition of item information, whereas recollection supports the recognition of associative information. Event Related Potential (ERP) studies provide support for dual process models, by demonstrating qualitatively distinct patterns of neural activity associated with familiarity (Mid-Frontal old/new effect) and recollection (Left-Parietal old/new effect). In the current thesis, ERPs were used to address two important questions regarding associative recognition – namely, the function of the neural signal supporting recollection and whether familiarity can contribute to the retrieval of novel associative information.
The first series of experiments was aimed at addressing how recollection operates by employing a recently developed continuous source task designed to directly measure the accuracy of retrieval success. To date, the function of recollection has been fiercely debated, with some arguing that recollection reflects the operation of a continuous retrieval process, whereby test cues always elicit some information from memory. Alternatively, recollection may reflect the operation of a thresholded process that allows for retrieval failure, whereby test cues sometimes elicit no information from memory at all. In the current thesis, the Left Parietal effect was found to be sensitive to the precision of memory responses when recollection succeeded, but was entirely absent when recollection failed. The result clarifies the nature of the neural mechanism underlying successful retrieval whilst also providing novel evidence in support of threshold models of recollection.
The second series of experiments addressed whether familiarity could contribute to the retrieval of novel associative information. Recent associative recognition studies have suggested that unitization (whereby multi-component stimuli are encoded as a single item rather than as a set of associated parts) can improve episodic memory by increasing the availability of familiarity during retrieval. To date, however, ERP studies have failed to provide any evidence of unitization for novel associations, whereas behavioural support for unitization is heavily reliant on model specific measures such as ROC analysis. Over three separate associative recognition studies employing unrelated word pairs, the magnitude of the Mid-Frontal old/new effect was found to be modulated by encoding instructions designed to manipulate the level of unitization. Importantly, the results also suggest that different encoding strategies designed to manipulate the level of unitization may be more successful than others. Finally, the results also revealed that differences in behavioural performance and modulation of the Mid-Frontal old/new effect between unitized and non-unitized instructions is greater for unrelated compared to related word pairs. In essence, the results suggest that unitization is better suited to learning completely novel associations as opposed to word pairs sharing a pre-existing conceptual relationship.
Overall, the data presented in this thesis supports dual process accounts of episodic memory, suggesting that at a neural level of analysis, recollection is both thresholded and variable, whilst also supporting the assumption that familiarity can contribute to successful retrieval of novel associative information. The results have important implications for our current understanding of cognitive decline and the development of behavioural interventions aimed at alleviating associative deficits
Hippocampal alterations after SARS-CoV-2 infection: a systematic review
SARS-CoV-2 infection produces a wide range of symptoms. Some of the structural changes caused by the virus in the nervous system are found in the medial temporal lobe, and several neuropsychological sequelae of COVID-19 are related to the function of the hippocampus. The main objective of the systematic review is to update and further analyze the existing evidence of hippocampal and related cortices’ structural and functional alterations due to SARS-CoV-2 infection. Both clinical and preclinical studies that used different methodologies to explore the effects of this disease at different stages and grades of severity were considered, besides exploring related cognitive and emotional symptomatology. A total of 24 studies were identified by searching in SCOPUS, Web Of Science (WOS), PubMed, and PsycInfo databases up to October 3rd, 2022. Thirteen studies were performed in clinical human samples, 9 included preclinical animal models, 3 were performed post-mortem, and 1 included both post-mortem and preclinical samples. Alterations in the hippocampus were detected in the acute stage and after several months of infection. Clinical studies revealed alterations in hippocampal connectivity and metabolism. Memory alterations correlated with altered metabolic profiles or changes in grey matter volumes. Hippocampal human postmortem and animal studies observed alterations in neurogenesis, dendrites, and immune response, besides high apoptosis and neuroinflammation. Preclinical studies reported the viral load in the hippocampus. Olfactory dysfunction was associated with alterations in brain functionality. Several clinical studies revealed cognitive complaints, neuropsychological alterations, and depressive and anxious symptomatology
Examining the learning burden and decay of second language vocabulary knowledge
Research in second language (L2) vocabulary learning has shown that not all words are equally easy to learn, and that several factors affect the difficulty with which words are acquired, i.e., their learning burden. However, research to date has explored only a few of the many factors affecting learning burden and existing findings are inconclusive. Another important finding in the L2 vocabulary learning literature is that L2 lexical knowledge is forgotten after learning but, to date, there has been minimal investigation of the variables that influence lexical decay. It has also been assumed that the lexical items most difficult to acquire are those easiest to forget, pointing towards a positive relationship between learning burden and decay (Webb & Nation, 2017). However, there is currently limited empirical evidence to support this assumption. This thesis reports research undertaken to explore the effect of different variables on learning burden and lexical decay, and the relationship between burden and decay. It consists of three empirical studies that investigated the effect of intralexical (i.e., part of speech, word length), contextual (i.e., meaning presentation code, form presentation mode), and individual (i.e., perceived target item usefulness, language learning aptitude) factors on the learning burden and decay of vocabulary knowledge that was intentionally learned with flashcard software. Each study also considered the effect of learning burden on lexical decay. Additionally, a cross-study analysis was conducted to explore the effect of the retention interval length on decay. The empirical studies showed that word length, aspects of language learning aptitude, and form presentation mode impacted learning burden but not decay, with shorter words, higher associative memory capacity, and bimodal form presentation related to less burden. Perceived target item usefulness was found to have no effect on burden or decay. Meaning presentation code and PoS were found to affect both burden and decay. Lexical items presented with an L2 definition and verbs were more burdensome and more likely to decay than items presented with an L1 equivalent and nouns. The findings also indicated that more learning burden was associated with a higher likelihood of decay. The cross-study analysis showed that decay was not directly proportional to the retention interval length and that form recall knowledge was more susceptible to decay than form recognition. Additionally, this thesis explores implications for vocabulary research and L2 pedagogy
Body patterning and cognition in cephalopods - a literature review
Cephalopods are a valuable model for studying the evolution of cognition due to their distinctive brain structure, organisation, and connectivity patterns compared to vertebrates. The development of large brains and behavioural complexities are believed to be triggered by evolutionary pressures stemming from factors like heightened predation, more demanding foraging conditions, and intense mating competition. While the differences between corvid and mammals are less pronounced, the cephalopod brain is closer to the vertebrate brain in terms of encephalisation of ganglionic masses observed by nerve cell clusters. The cerebral ganglion in cephalopods is similar to the vertebrate forebrain and midbrain, while the vertical lobe is similar to the vertebrate cerebral cortex and hippocampus formation, which are involved in learning and memory. These brain regions function in a hierarchical system and are intimately connected with their eyes and optic lobes where visual inputs are processed, motor commands are transmitted to the lower motor centre. Chromatophores are skin elements and the physiological control of body patterning and are visually driven and light sensitive. This sets cephalopods apart from their molluscan families such as gastropods and bivalves. Recent studies have revealed that the opsins present in the skin are like those occurring in the retina. This infers that the connection between visual processing and body patterns is not exclusively innate. Expanding on Macphail's Null Hypothesis which posits no significant qualitative or quantitative differences in intelligence across vertebrates, this study seeks to explore the link between body patterning and cognitive abilities across cephalopod species. By comparing patterns of similarities and differences in cognitive abilities, this study aims to investigate whether body patterning can serve as an indicator of cognitive capacity. In conclusion, the study finds the presence of interindividual variations within species and disparities across different species in both body patterning and cognitive abilities. There are associations between cognitive capacity and body patterns. However, establishing a direct and conclusive connection between high-level cognitive abilities and the expression of body patterns remains elusive, as concrete evidence supporting such a relationship is lacking.Cephalopoda utgör en värdefull modell för att studera den kognitiva evolutionen på grund av deras distinkta hjärnstruktur, organisation och nervernas kontaktmönster jämfört med ryggradsdjur. Utvecklingen av stora hjärnor och komplexa beteenden tros vara resultatet av evolutionär press från faktorer som ökad predation, mer krävande födosökningsförhållanden och intensiv parningskonkurrens. Medan skillnaderna mellan kråkfåglar och däggdjur är mindre uttalade, är bläckfiskhjärnan närmare ryggradsdjurshjärnan när det gäller encefalisering av nervcellkluster. Det cerebrala ganglie hos bläckfiskar liknar ryggradsdjurens främre hjärna och mellanhjärna, medan den vertikala loben liknar ryggradsdjurens hjärnbark och hippocampusformation, som är involverade i inlärning och minne. Dessa hjärnregioner fungerar inom ett hierarkiskt system och är intimt kopplade till deras ögon och optiska lober där visuell information bearbetas och motoriska kommandon överförs till de nedre motoriska centrarna. Kromatoforer är hudstrukturer som fysiologiskt kontrollerar kroppsmönster och är visuellt styrda och ljuskänsliga. Detta skiljer cephalopoder från andra molluskfamiljer som gastropoder och musslor. Studier har nyligenavslöjat att de opsin som finns i huden liknar de som förekommer i näthinnan. Detta antyder att sambandet mellan visuell bearbetning och kroppsmönster inte är uteslutande medfödd. Utöver Macphails nollhypotes, som hävdar att det inte finns några signifikanta kvalitativa eller kvantitativa skillnader i intelligens mellan ryggradsdjur, ämnar denna studie utforska kopplingen mellan kroppsmönster och kognitiva förmågor hos cephalopoda. Genom att jämföra likheter och skillnader i kognitiva förmågor syftar denna studie till att undersöka om kroppsmönster kan fungera som en indikator på kognitiv kapacitet. Resultaten visar på förekomst av variationer mellan individer inom arter och skillnader mellan olika arter både vad gäller kroppsmönster och kognitiva förmågor. Det finns samband mellan kognitiv kapacitet och funktioner samt kroppsmönster. Dock är det fortfarande svårt att fastställa en direkt och definitiv koppling mellan hög kognitiva förmågor och uttrycket av kroppsmönster, eftersom konkret bevis som stöder ett sådant samband saknas
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