Power laws, memory capacity, and self-tuned critical branching in an LIF model with binary synapses

Both fluctuations and distributions of spontaneous neural spiking activity have been observed to closely follow a variety of power laws. Multiple explanations have been offered for each observation, but few lead to mechanisms that encompass their widespread occurrence. A canonical, leaky integrate-and-fire model is presented in which synapses are updated based on the timing of pre- and post-synaptic spikes in order to maintain a state of critical branching. Results showed that 1) the self-tuning algorithm maintained critical branching under a range of parameters; 2) power laws were obtained in spiking activity fluctuations (1/f scaling), size distributions of network bursts (neural avalanches), and temporal correlations in interspike intervals (Allan factor); 3) power laws disappeared once the self-tuning algorithm was disabled; and 4) critical branching was adaptive in that it maximized the network’s memory capacity when assessed as a liquid state machine

Academic Placement Data and Analysis: 2016 Final Report

Academic Placement Data and Analysis (APDA), a project funded by the American Philosophical Association (APA) and headed by Carolyn Dicey Jennings (UC Merced), aims “to make information on academic job placement useful to prospective graduate students in philosophy.” The project has just been updated to include new data, which Professor Jennings describes in a post at New APPS. She also announces a new interactive data tool with which one can sift through and sort information. (from Daily Nous

Distinct spatial arrangements of ACE2 and TMPRSS2 expression in Syrian hamster lung lobes dictates SARS-CoV-2 infection patterns

SARS-CoV-2 attaches to angiotensin-converting enzyme 2 (ACE2) to gain entry into cells after which the spike protein is cleaved by the transmembrane serine protease 2 (TMPRSS2) to facilitate viral-host membrane fusion. ACE2 and TMPRSS2 expression profiles have been analyzed at the genomic, transcriptomic, and single-cell RNAseq levels. However, transcriptomic data and actual protein validation convey conflicting information regarding the distribution of the biologically relevant protein receptor in whole tissues. To describe the organ-level architecture of receptor expression, related to the ability of ACE2 and TMPRSS2 to mediate infectivity, we performed a volumetric analysis of whole Syrian hamster lung lobes. Lung tissue of infected and control animals was stained using antibodies against ACE2 and TMPRSS2, combined with SARS-CoV-2 nucleoprotein staining. This was followed by light-sheet microscopy imaging to visualize their expression and related infection patterns. The data demonstrate that infection is restricted to sites containing both ACE2 and TMPRSS2, the latter is expressed in the primary and secondary bronchi whereas ACE2 is predominantly observed in the bronchioles and alveoli. Conversely, infection completely overlaps where ACE2 and TMPRSS2 co-localize in the tertiary bronchi, bronchioles, and alveoli

Two-component spike nanoparticle vaccine protects macaques from SARS-CoV-2 infection

Brouwer et al. present preclinical evidence in support of a COVID-19 vaccine candidate, designed as a self-assembling two-component protein nanoparticle displaying multiple copies of the SARS-CoV-2 spike protein, which induces strong neutralizing antibody responses and protects from high-dose SARS-CoV-2 challenge.The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is continuing to disrupt personal lives, global healthcare systems, and economies. Hence, there is an urgent need for a vaccine that prevents viral infection, transmission, and disease. Here, we present a two-component protein-based nanoparticle vaccine that displays multiple copies of the SARS-CoV-2 spike protein. Immunization studies show that this vaccine induces potent neutralizing antibody responses in mice, rabbits, and cynomolgus macaques. The vaccine-induced immunity protects macaques against a high-dose challenge, resulting in strongly reduced viral infection and replication i

The Role of Spatial Structure and Memory in Human Foraging

Foraging is an essential process for all mobile organisms. It allows organisms to locate resources such as food and mates. There is a long history of research on animal foraging in the ecology literature and recent work in cognitive science has revealed similarities between cognitive search behaviors and animal foraging behaviors. This gives rise to the possibility of bringing the rich animal foraging literature to bear on cognitive search processes. Historically there have been several major approaches to the study and modeling of foraging animals. One approach is known as optimal foraging theory which is focused on optimizing the amount of time an organism spends foraging a single location before moving on to another location. Another is an expansion on that approach which operationalizes those ideas into a spatial model known as area-restricted search. A third approach is known as the Lévy flight hypothesis. It focuses on the longer term distributional properties of foraging animals, and optimizes coverage of a given search space. These approaches all make assumptions about environmental conditions faced by foraging organisms. The degree of resource sparsity and clustering in a foraging environment are believed to be important, but it is unclear how they affect foraging behaviors. Additionally spatial memory is a key concept important to animal search strategies, but is frequently ignored in the existing literature. For this dissertation, a series of experiments utilized a web-based foraging game to test how these variables affect foraging behaviors. The first experiment demonstrated that the degree of clustering in the environment had a significant impact on search strategies, and provided qualitative evidence that memory played a role in people’s search behaviors. The experiments revealed distributional patterns very similar to those predicted by the Lévy flight approach. The second experiment refined the method and directly tested memory cues and a broader range of resource densities. This experiment revealed results similar to the first with the addition of significant effects of both memory cues and resource density. This dissertation then discusses a model that combined key concepts from both optimal foraging and Lévy foraging to produce results very similar to those produced by human participants, but with significantly higher performance. Experiment 3 examined how human performance changes when specific advantages are provided that can be found in our model, including perfect memory and accuracy. Finally a continuation of the model is discussed that explores the dynamics of multiple foragers searching the same space. Overall, I demonstrate that people will generate Lévy-like search distributions in a wide variety of environmental conditions, but that search strategies will alter based on the current environment. I also demonstrate that spatial memory is a key factor in foraging, and provide a simple memory-based model that produces foraging behavior very similar to those utilized by people

Der Weltumsegler : Johann Georg Adam Forster, 1754-1794.

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