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1.
Proc Natl Acad Sci U S A ; 120(32): e2300558120, 2023 08 08.
Artículo en Inglés | MEDLINE | ID: mdl-37523562

RESUMEN

While sensory representations in the brain depend on context, it remains unclear how such modulations are implemented at the biophysical level, and how processing layers further in the hierarchy can extract useful features for each possible contextual state. Here, we demonstrate that dendritic N-Methyl-D-Aspartate spikes can, within physiological constraints, implement contextual modulation of feedforward processing. Such neuron-specific modulations exploit prior knowledge, encoded in stable feedforward weights, to achieve transfer learning across contexts. In a network of biophysically realistic neuron models with context-independent feedforward weights, we show that modulatory inputs to dendritic branches can solve linearly nonseparable learning problems with a Hebbian, error-modulated learning rule. We also demonstrate that local prediction of whether representations originate either from different inputs, or from different contextual modulations of the same input, results in representation learning of hierarchical feedforward weights across processing layers that accommodate a multitude of contexts.


Asunto(s)
Modelos Neurológicos , N-Metilaspartato , Aprendizaje/fisiología , Neuronas/fisiología , Percepción
2.
Proc Natl Acad Sci U S A ; 120(11): e2217422120, 2023 03 14.
Artículo en Inglés | MEDLINE | ID: mdl-36888663

RESUMEN

Somatic mutations are highly enriched at transcription factor (TF) binding sites, with the strongest trend being observed for ultraviolet light (UV)-induced mutations in melanomas. One of the main mechanisms proposed for this hypermutation pattern is the inefficient repair of UV lesions within TF-binding sites, caused by competition between TFs bound to these lesions and the DNA repair proteins that must recognize the lesions to initiate repair. However, TF binding to UV-irradiated DNA is poorly characterized, and it is unclear whether TFs maintain specificity for their DNA sites after UV exposure. We developed UV-Bind, a high-throughput approach to investigate the impact of UV irradiation on protein-DNA binding specificity. We applied UV-Bind to ten TFs from eight structural families, and found that UV lesions significantly altered the DNA-binding preferences of all the TFs tested. The main effect was a decrease in binding specificity, but the precise effects and their magnitude differ across factors. Importantly, we found that despite the overall reduction in DNA-binding specificity in the presence of UV lesions, TFs can still compete with repair proteins for lesion recognition, in a manner consistent with their specificity for UV-irradiated DNA. In addition, for a subset of TFs, we identified a surprising but reproducible effect at certain nonconsensus DNA sequences, where UV irradiation leads to a high increase in the level of TF binding. These changes in DNA-binding specificity after UV irradiation, at both consensus and nonconsensus sites, have important implications for the regulatory and mutagenic roles of TFs in the cell.


Asunto(s)
Factores de Transcripción , Rayos Ultravioleta , Humanos , Factores de Transcripción/metabolismo , Sitios de Unión/genética , Unión Proteica/genética , ADN/metabolismo
3.
PLoS Comput Biol ; 18(8): e1010353, 2022 08.
Artículo en Inglés | MEDLINE | ID: mdl-35960767

RESUMEN

Simulations of neural activity at different levels of detail are ubiquitous in modern neurosciences, aiding the interpretation of experimental data and underlying neural mechanisms at the level of cells and circuits. Extracellular measurements of brain signals reflecting transmembrane currents throughout the neural tissue remain commonplace. The lower frequencies (≲ 300Hz) of measured signals generally stem from synaptic activity driven by recurrent interactions among neural populations and computational models should also incorporate accurate predictions of such signals. Due to limited computational resources, large-scale neuronal network models (≳ 106 neurons or so) often require reducing the level of biophysical detail and account mainly for times of action potentials ('spikes') or spike rates. Corresponding extracellular signal predictions have thus poorly accounted for their biophysical origin. Here we propose a computational framework for predicting spatiotemporal filter kernels for such extracellular signals stemming from synaptic activity, accounting for the biophysics of neurons, populations, and recurrent connections. Signals are obtained by convolving population spike rates by appropriate kernels for each connection pathway and summing the contributions. Our main results are that kernels derived via linearized synapse and membrane dynamics, distributions of cells, conduction delay, and volume conductor model allow for accurately capturing the spatiotemporal dynamics of ground truth extracellular signals from conductance-based multicompartment neuron networks. One particular observation is that changes in the effective membrane time constants caused by persistent synapse activation must be accounted for. The work also constitutes a major advance in computational efficiency of accurate, biophysics-based signal predictions from large-scale spike and rate-based neuron network models drastically reducing signal prediction times compared to biophysically detailed network models. This work also provides insight into how experimentally recorded low-frequency extracellular signals of neuronal activity may be approximately linearly dependent on spiking activity. A new software tool LFPykernels serves as a reference implementation of the framework.


Asunto(s)
Modelos Neurológicos , Neuronas , Potenciales de Acción/fisiología , Encéfalo/fisiología , Simulación por Computador , Neuronas/fisiología
4.
BMC Health Serv Res ; 23(1): 1413, 2023 Dec 14.
Artículo en Inglés | MEDLINE | ID: mdl-38098079

RESUMEN

BACKGROUND: Low- and middle-income countries often lack access to mental health services, leading to calls for integration within other primary care systems. In sub-Saharan Africa, integration of depression treatment in non-communicable disease (NCD) settings is feasible, acceptable, and effective. However, leadership and implementation climate challenges often hinder effective integration and quality of services. The aim of this study was to identify discrete leadership strategies that facilitate overcoming barriers to the integration of depression care in NCD clinics in Malawi and to understand how clinic leadership shapes the implementation climate. METHODS: We conducted 39 in-depth interviews with the District Medical Officer, the NCD coordinator, one NCD provider, and the research assistant from each of the ten Malawian NCD clinics (note one District Medical Officer served two clinics). Based on semi-structured interview guides, participants were asked their perspectives on the impact of leadership and implementation climate on overcoming barriers to integrating depression care into existing NCD services. Thematic analysis used both inductive and deductive approaches to identify emerging themes and compare among participant type. RESULTS: The results revealed how engaged leadership can fuel a positive implementation climate where clinics had heightened capacity to overcome implementation barriers. Effective leaders were approachable and engaged in daily operations of the clinic and problem-solving. They held direct involvement with and mentorship during the intervention, providing assistance in patient screening and consultation with treatment plans. Different levels of leadership utilized their respective standings and power dynamics to influence provider attitudes and perceptions surrounding the intervention. Leaders acted by informing providers about the intervention source and educating them on the importance of mental healthcare, as it was often undervalued. Lastly, they prioritized teamwork and collective ownership for the intervention, increasing provider responsibility. CONCLUSION: Training that prioritizes leadership visibility and open communication will facilitate ongoing Malawi Ministry of Health efforts to scale up evidence-based depression treatment within NCD clinics. This proves useful where extensive and external monitoring may be limited. Ultimately, these results can inform successful strategies to close implementation gaps to achieve integration of mental health services in low-resource settings through improved leadership and implementation climate. TRIAL REGISTRATION: These findings are reported from ClinicalTrials.gov, NCT03711786. Registered on 18/10/2018. https://clinicaltrials.gov/ct2/show/NCT03711786 .


Asunto(s)
Depresión , Enfermedades no Transmisibles , Humanos , Depresión/terapia , Enfermedades no Transmisibles/terapia , Liderazgo , Malaui , Atención a la Salud/métodos
5.
PLoS Comput Biol ; 16(8): e1007790, 2020 08.
Artículo en Inglés | MEDLINE | ID: mdl-32841234

RESUMEN

The impairment of cognitive function in Alzheimer's disease is clearly correlated to synapse loss. However, the mechanisms underlying this correlation are only poorly understood. Here, we investigate how the loss of excitatory synapses in sparsely connected random networks of spiking excitatory and inhibitory neurons alters their dynamical characteristics. Beyond the effects on the activity statistics, we find that the loss of excitatory synapses on excitatory neurons reduces the network's sensitivity to small perturbations. This decrease in sensitivity can be considered as an indication of a reduction of computational capacity. A full recovery of the network's dynamical characteristics and sensitivity can be achieved by firing rate homeostasis, here implemented by an up-scaling of the remaining excitatory-excitatory synapses. Mean-field analysis reveals that the stability of the linearised network dynamics is, in good approximation, uniquely determined by the firing rate, and thereby explains why firing rate homeostasis preserves not only the firing rate but also the network's sensitivity to small perturbations.


Asunto(s)
Enfermedad de Alzheimer/fisiopatología , Modelos Neurológicos , Red Nerviosa/fisiopatología , Sinapsis/fisiología , Homeostasis/fisiología , Humanos
6.
J Health Commun ; 26(3): 147-160, 2021 03 04.
Artículo en Inglés | MEDLINE | ID: mdl-33779520

RESUMEN

Comprehensive sexual health education (SHE) is an effective strategy for improving adolescent sexual health. However, few of these programs address media influence on sexual cognitions and behaviors. Also, more research is needed on using web-based instruction for SHE. Seventeen classes (N = 331 students) in one high school in the United States were enrolled in a pre-post randomized controlled trial to assess the feasibility of Media Aware, a web-based SHE program that uses a media literacy education (MLE) approach. Compared to a delayed-intervention group, students who received Media Aware had significant reductions in their perceived realism of and similarity to media messaging, improved cognitive elaboration of media messages, more realistic perceptions of teen sex norms and risky sex norms, increased efficacy and intention to act as a bystander to potential sexual assault, increased intent to communicate before sex, and increased efficacy to use contraception/protection. These students reported being less willing to hook up, being less willing to have unprotected sex (for males), and positive feedback on their experiences using a web-based program. This study provides evidence that web-based MLE sexual health programming is a feasible and acceptable strategy for improving media-related and sexual health outcomes among adolescents.


Asunto(s)
Intervención basada en la Internet , Servicios de Salud Escolar , Salud Sexual/educación , Estudiantes/psicología , Adolescente , Estudios de Factibilidad , Femenino , Alfabetización en Salud , Humanos , Masculino , Medios de Comunicación de Masas , Evaluación de Programas y Proyectos de Salud , Instituciones Académicas , Estudiantes/estadística & datos numéricos , Estados Unidos
7.
PLoS Comput Biol ; 15(4): e1006781, 2019 04.
Artículo en Inglés | MEDLINE | ID: mdl-31022182

RESUMEN

Complexity and heterogeneity are intrinsic to neurobiological systems, manifest in every process, at every scale, and are inextricably linked to the systems' emergent collective behaviours and function. However, the majority of studies addressing the dynamics and computational properties of biologically inspired cortical microcircuits tend to assume (often for the sake of analytical tractability) a great degree of homogeneity in both neuronal and synaptic/connectivity parameters. While simplification and reductionism are necessary to understand the brain's functional principles, disregarding the existence of the multiple heterogeneities in the cortical composition, which may be at the core of its computational proficiency, will inevitably fail to account for important phenomena and limit the scope and generalizability of cortical models. We address these issues by studying the individual and composite functional roles of heterogeneities in neuronal, synaptic and structural properties in a biophysically plausible layer 2/3 microcircuit model, built and constrained by multiple sources of empirical data. This approach was made possible by the emergence of large-scale, well curated databases, as well as the substantial improvements in experimental methodologies achieved over the last few years. Our results show that variability in single neuron parameters is the dominant source of functional specialization, leading to highly proficient microcircuits with much higher computational power than their homogeneous counterparts. We further show that fully heterogeneous circuits, which are closest to the biophysical reality, owe their response properties to the differential contribution of different sources of heterogeneity.


Asunto(s)
Corteza Cerebral/fisiología , Biología Computacional , Memoria/fisiología , Modelos Neurológicos , Neuronas/fisiología , Potenciales de Acción/fisiología , Animales , Humanos , Ratones , Redes Neurales de la Computación , Sinapsis/fisiología
8.
Eur J Neurosci ; 49(6): 737-753, 2019 03.
Artículo en Inglés | MEDLINE | ID: mdl-29917291

RESUMEN

The basal ganglia have been hypothesized to be involved in action selection, i.e. resolving competition between simultaneously activated motor programs. It has been shown that the direct pathway facilitates action execution whereas the indirect pathway inhibits it. However, as the pathways are both active during an action, it remains unclear whether their role is co-operative or competitive. In order to investigate this issue, we developed a striatal model consisting of D1 and D2 medium spiny neurons (MSNs) and interfaced it to a simulated robot moving in an environment. We demonstrate that this model is able to reproduce key behavioral features of several experiments involving optogenetic manipulation of the striatum, such as freezing and ambulation. We then investigate the interaction of D1- and D2-MSNs. We find that their fundamental relationship is co-operative within a channel and competitive between channels; this turns out to be crucial for action selection. However, individual pairs of D1- and D2-MSNs may exhibit predominantly competition or co-operation depending on their distance, and D1- and D2-MSNs population activity can alternate between co-operation and competition modes during a stimulation. Additionally, our results show that D2-D2 connectivity between channels is necessary for effective resolution of competition; in its absence, a conflict of two motor programs typically results in neither being selected.


Asunto(s)
Cuerpo Estriado/metabolismo , Neuronas Dopaminérgicas/metabolismo , Neostriado/fisiopatología , Receptores de Dopamina D1/metabolismo , Receptores de Dopamina D2/metabolismo , Animales , Cuerpo Estriado/fisiopatología , Ratones Transgénicos , Neostriado/metabolismo , Neuritas/metabolismo , Procedimientos Quirúrgicos Robotizados
9.
J Comput Neurosci ; 39(1): 77-103, 2015 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-26041729

RESUMEN

Dynamics and function of neuronal networks are determined by their synaptic connectivity. Current experimental methods to analyze synaptic network structure on the cellular level, however, cover only small fractions of functional neuronal circuits, typically without a simultaneous record of neuronal spiking activity. Here we present a method for the reconstruction of large recurrent neuronal networks from thousands of parallel spike train recordings. We employ maximum likelihood estimation of a generalized linear model of the spiking activity in continuous time. For this model the point process likelihood is concave, such that a global optimum of the parameters can be obtained by gradient ascent. Previous methods, including those of the same class, did not allow recurrent networks of that order of magnitude to be reconstructed due to prohibitive computational cost and numerical instabilities. We describe a minimal model that is optimized for large networks and an efficient scheme for its parallelized numerical optimization on generic computing clusters. For a simulated balanced random network of 1000 neurons, synaptic connectivity is recovered with a misclassification error rate of less than 1 % under ideal conditions. We show that the error rate remains low in a series of example cases under progressively less ideal conditions. Finally, we successfully reconstruct the connectivity of a hidden synfire chain that is embedded in a random network, which requires clustering of the network connectivity to reveal the synfire groups. Our results demonstrate how synaptic connectivity could potentially be inferred from large-scale parallel spike train recordings.


Asunto(s)
Potenciales de Acción/fisiología , Modelos Neurológicos , Red Nerviosa/fisiología , Neuronas/fisiología , Sinapsis/fisiología , Animales , Simulación por Computador , Conectoma , Humanos , Modelos Lineales , Dinámicas no Lineales
10.
Trauma Violence Abuse ; 25(1): 846-861, 2024 01.
Artículo en Inglés | MEDLINE | ID: mdl-37078533

RESUMEN

This systematic review sought to describe the prevalence of intimate partner violence (IPV) victimization among immigrants in the United States (U.S.) and the prevalence of IPV perpetration among immigrants in the U.S. PsycInfo, PubMed, Global Health and Scopus databases were searched for peer-reviewed literature that quantitatively examined IPV in relation to immigration. Twenty-four articles were included in the final review. Past-year IPV victimization rates among immigrants ranged from 3.8% to 46.9% and lifetime IPV victimization rates ranged from 13.9% to 93%; past-year IPV perpetration rates ranged from 3.0% to 24.8% and the one lifetime IPV perpetration rate was 12.8%. Estimates varied widely by country of origin, type of violence measured, and measure used to quantify IPV. Reliance on small convenience samples is problematic when trying to determine the true prevalence of IPV among immigrants. Epidemiological research is needed to improve the accuracy and representativeness of findings.


Asunto(s)
Acoso Escolar , Víctimas de Crimen , Emigrantes e Inmigrantes , Violencia de Pareja , Humanos , Estados Unidos/epidemiología , Emigración e Inmigración
11.
Front Neuroinform ; 18: 1156683, 2024.
Artículo en Inglés | MEDLINE | ID: mdl-38410682

RESUMEN

Integration of information across heterogeneous sources creates added scientific value. Interoperability of data, tools and models is, however, difficult to accomplish across spatial and temporal scales. Here we introduce the toolbox Parallel Co-Simulation, which enables the interoperation of simulators operating at different scales. We provide a software science co-design pattern and illustrate its functioning along a neuroscience example, in which individual regions of interest are simulated on the cellular level allowing us to study detailed mechanisms, while the remaining network is efficiently simulated on the population level. A workflow is illustrated for the use case of The Virtual Brain and NEST, in which the CA1 region of the cellular-level hippocampus of the mouse is embedded into a full brain network involving micro and macro electrode recordings. This new tool allows integrating knowledge across scales in the same simulation framework and validating them against multiscale experiments, thereby largely widening the explanatory power of computational models.

12.
BMJ Open Qual ; 13(1)2024 02 13.
Artículo en Inglés | MEDLINE | ID: mdl-38351031

RESUMEN

INTRODUCTION: Quality improvement collaboratives (QICs) are a common approach to facilitate practice change and improve care delivery. Attention to QIC implementation processes and outcomes can inform best practices for designing and delivering collaborative content. In partnership with a clinically integrated network, we evaluated implementation outcomes for a virtual QIC with independent primary care practices delivered during COVID-19. METHODS: We conducted a longitudinal case study evaluation of a virtual QIC in which practices participated in bimonthly online meetings and monthly tailored QI coaching sessions from July 2020 to June 2021. Implementation outcomes included: (1) level of engagement (meeting attendance and poll questions), (2) QI capacity (assessments completed by QI coaches), (3) use of QI tools (plan-do-check-act (PDCA) cycles started and completed) and (4) participant perceptions of acceptability (interviews and surveys). RESULTS: Seven clinics from five primary care practices participated in the virtual QIC. Of the seven sites, five were community health centres, three were in rural counties and clinic size ranged from 1 to 7 physicians. For engagement, all practices had at least one member attend all online QIC meetings and most (9/11 (82%)) poll respondents reported meeting with their QI coach at least once per month. For QI capacity, practice-level scores showed improvements in foundational, intermediate and advanced QI work. For QI tools used, 26 PDCA cycles were initiated with 9 completed. Most (10/11 (91%)) survey respondents were satisfied with their virtual QIC experience. Twelve interviews revealed additional themes such as challenges in obtaining real-time data and working with multiple electronic medical record systems. DISCUSSION: A virtual QIC conducted with independent primary care practices during COVID-19 resulted in high participation and satisfaction. QI capacity and use of QI tools increased over 1 year. These implementation outcomes suggest that virtual QICs may be an attractive alternative to engage independent practices in QI work.


Asunto(s)
COVID-19 , Mejoramiento de la Calidad , Humanos , Conducta Cooperativa , Instituciones de Atención Ambulatoria , Atención Primaria de Salud/métodos
13.
J Vis Exp ; (203)2024 Jan 05.
Artículo en Inglés | MEDLINE | ID: mdl-38251777

RESUMEN

Patient-derived organoid (PDO) models of cancer are a multifunctional research system that better recapitulates human disease as compared to cancer cell lines. PDO models can be generated by culturing patient tumor cells in extracellular basement membrane extracts (BME) and plating them as three-dimensional domes. However, commercially available reagents that have been optimized for phenotypic assays in monolayer cultures often are not compatible with BME. Herein, we describe a method to plate PDO models and assess drug effects using an automated live-cell imaging system. In addition, we apply fluorescent dyes that are compatible with kinetic measurements to quantify cell health and apoptosis simultaneously. Image capture can be customized to occur at regular time intervals over several days. Users can analyze drug effects in individual Z-plane images or a Z Projection of serial images from multiple focal planes. Using masking, specific parameters of interest are calculated, such as PDO number, area, and fluorescence intensity. We provide proof-of-concept data demonstrating the effect of cytotoxic agents on cell health, apoptosis, and viability. This automated kinetic imaging platform can be expanded to other phenotypic readouts to understand diverse therapeutic effects in PDO models of cancer.


Asunto(s)
Apoptosis , Neoplasias , Humanos , Membrana Basal , Bioensayo , Línea Celular , Organoides
14.
Lancet Glob Health ; 12(4): e662-e671, 2024 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-38408461

RESUMEN

BACKGROUND: Depression is a major contributor to morbidity and mortality in sub-Saharan Africa. Due to low system capacity, three in four patients with depression in sub-Saharan Africa go untreated. Despite this, little attention has been paid to the cost-effectiveness of implementation strategies to scale up evidence-based depression treatment in the region. In this study, we investigate the cost-effectiveness of two different implementation strategies to integrate the Friendship Bench approach and measurement-based care in non-communicable disease clinics in Malawi. METHODS: The two implementation strategies tested in this study are part of a trial, in which ten clinics were randomly assigned (1:1) to a basic implementation package consisting of an internal coordinator acting as a champion (IC-only group) or to an enhanced package that complemented the basic package with quarterly external supervision, and audit and feedback of intervention delivery (IC + ES group). We included material costs, training costs, costs related to project-wide meetings, transportation and medication costs, time costs related to internal champion activities and depression screening or treatment, and costs of external supervision visits if applicable. Outcomes included the number of patients screened with the patient health questionnaire 2 (PHQ-2), cases of remitted depression at 3 and 12 months, and disability-adjusted life-years (DALYs) averted. We compared the cost-effectiveness of both packages to the status quo (ie, no intervention) using a micro-costing-informed decision-tree model. FINDINGS: Relative to the status quo, IC + ES would be on average US$10 387 ($1349-$17 365) more expensive than IC-only but more effective in achieving remission and averting DALYs. The cost per additional remission would also be lower with IC + ES than IC-only at 3 months ($119 vs $223) and 12 months ($210 for IC + ES; IC-only dominated by the status quo at 12 months). Neither package would be cost-effective under the willingness-to-pay threshold of $65 per DALY averted currently used by the Malawian Ministry of Health. However, the IC + ES package would be cost-effective in relation to the commonly used threshold of three times per-capita gross domestic product per DALY averted. INTERPRETATION: Investing in supporting champions might be an appropriate use of resources. Although not currently cost-effective by Malawian willingness-to-pay standards compared with the status quo, the IC + ES package would probably be a cost-effective way to build mental health-care capacity in resource-constrained settings in which decision makers use higher willingness-to-pay thresholds. FUNDING: National Institute of Mental Health.


Asunto(s)
Salud Mental , Humanos , Análisis Costo-Beneficio , Malaui
15.
Front Integr Neurosci ; 17: 935177, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-37396571

RESUMEN

To acquire statistical regularities from the world, the brain must reliably process, and learn from, spatio-temporally structured information. Although an increasing number of computational models have attempted to explain how such sequence learning may be implemented in the neural hardware, many remain limited in functionality or lack biophysical plausibility. If we are to harvest the knowledge within these models and arrive at a deeper mechanistic understanding of sequential processing in cortical circuits, it is critical that the models and their findings are accessible, reproducible, and quantitatively comparable. Here we illustrate the importance of these aspects by providing a thorough investigation of a recently proposed sequence learning model. We re-implement the modular columnar architecture and reward-based learning rule in the open-source NEST simulator, and successfully replicate the main findings of the original study. Building on these, we perform an in-depth analysis of the model's robustness to parameter settings and underlying assumptions, highlighting its strengths and weaknesses. We demonstrate a limitation of the model consisting in the hard-wiring of the sequence order in the connectivity patterns, and suggest possible solutions. Finally, we show that the core functionality of the model is retained under more biologically-plausible constraints.

16.
Elife ; 122023 01 26.
Artículo en Inglés | MEDLINE | ID: mdl-36700545

RESUMEN

Information from the sensory periphery is conveyed to the cortex via structured projection pathways that spatially segregate stimulus features, providing a robust and efficient encoding strategy. Beyond sensory encoding, this prominent anatomical feature extends throughout the neocortex. However, the extent to which it influences cortical processing is unclear. In this study, we combine cortical circuit modeling with network theory to demonstrate that the sharpness of topographic projections acts as a bifurcation parameter, controlling the macroscopic dynamics and representational precision across a modular network. By shifting the balance of excitation and inhibition, topographic modularity gradually increases task performance and improves the signal-to-noise ratio across the system. We demonstrate that in biologically constrained networks, such a denoising behavior is contingent on recurrent inhibition. We show that this is a robust and generic structural feature that enables a broad range of behaviorally relevant operating regimes, and provide an in-depth theoretical analysis unraveling the dynamical principles underlying the mechanism.


Asunto(s)
Neocórtex , Neocórtex/fisiología , Relación Señal-Ruido , Redes Neurales de la Computación
17.
Sci Rep ; 13(1): 10517, 2023 06 29.
Artículo en Inglés | MEDLINE | ID: mdl-37386240

RESUMEN

Since dynamical systems are an integral part of many scientific domains and can be inherently computational, analyses that reveal in detail the functions they compute can provide the basis for far-reaching advances in various disciplines. One metric that enables such analysis is the information processing capacity. This method not only provides us with information about the complexity of a system's computations in an interpretable form, but also indicates its different processing modes with different requirements on memory and nonlinearity. In this paper, we provide a guideline for adapting the application of this metric to continuous-time systems in general and spiking neural networks in particular. We investigate ways to operate the networks deterministically to prevent the negative effects of randomness on their capacity. Finally, we present a method to remove the restriction to linearly encoded input signals. This allows the separate analysis of components within complex systems, such as areas within large brain models, without the need to adapt their naturally occurring inputs.


Asunto(s)
Cognición , Redes Neurales de la Computación
18.
bioRxiv ; 2023 Nov 17.
Artículo en Inglés | MEDLINE | ID: mdl-38014133

RESUMEN

Patient-derived organoid (PDO) models of cancer are a multifunctional research system that better recapitulates human disease as compared to cancer cell lines. PDO models can be generated by culturing patient tumor cells in extracellular basement membrane extracts (BME) and plating as three-dimensional domes. However, commercially available reagents that have been optimized for phenotypic assays in monolayer cultures often are not compatible with BME. Herein we describe a method to plate PDO models and assess drug effects using an automated live-cell imaging system. In addition, we apply fluorescent dyes that are compatible with kinetic measurements to simultaneously quantitate cell health and apoptosis. Image capture can be customized to occur at regular time intervals over several days. Users can analyze drug effects in individual Z-plane images or a Z Projection of serial images from multiple focal planes. Using masking, specific parameters of interest are calculated, such as PDO number, area, and fluorescence intensity. We provide proof-of-concept data demonstrating the effect of cytotoxic agents on cell health, apoptosis and viability. This automated kinetic imaging platform can be expanded to other phenotypic readouts to understand diverse therapeutic effects in PDO models of cancer.

19.
PLoS Comput Biol ; 7(5): e1001133, 2011 May.
Artículo en Inglés | MEDLINE | ID: mdl-21589888

RESUMEN

An open problem in the field of computational neuroscience is how to link synaptic plasticity to system-level learning. A promising framework in this context is temporal-difference (TD) learning. Experimental evidence that supports the hypothesis that the mammalian brain performs temporal-difference learning includes the resemblance of the phasic activity of the midbrain dopaminergic neurons to the TD error and the discovery that cortico-striatal synaptic plasticity is modulated by dopamine. However, as the phasic dopaminergic signal does not reproduce all the properties of the theoretical TD error, it is unclear whether it is capable of driving behavior adaptation in complex tasks. Here, we present a spiking temporal-difference learning model based on the actor-critic architecture. The model dynamically generates a dopaminergic signal with realistic firing rates and exploits this signal to modulate the plasticity of synapses as a third factor. The predictions of our proposed plasticity dynamics are in good agreement with experimental results with respect to dopamine, pre- and post-synaptic activity. An analytical mapping from the parameters of our proposed plasticity dynamics to those of the classical discrete-time TD algorithm reveals that the biological constraints of the dopaminergic signal entail a modified TD algorithm with self-adapting learning parameters and an adapting offset. We show that the neuronal network is able to learn a task with sparse positive rewards as fast as the corresponding classical discrete-time TD algorithm. However, the performance of the neuronal network is impaired with respect to the traditional algorithm on a task with both positive and negative rewards and breaks down entirely on a task with purely negative rewards. Our model demonstrates that the asymmetry of a realistic dopaminergic signal enables TD learning when learning is driven by positive rewards but not when driven by negative rewards.


Asunto(s)
Dopamina/fisiología , Aprendizaje/fisiología , Modelos Neurológicos , Plasticidad Neuronal/fisiología , Recompensa , Potenciales de Acción/fisiología , Algoritmos , Animales , Humanos , Red Nerviosa , Ratas
20.
Front Neuroinform ; 16: 884033, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35846779

RESUMEN

Despite the great strides neuroscience has made in recent decades, the underlying principles of brain function remain largely unknown. Advancing the field strongly depends on the ability to study large-scale neural networks and perform complex simulations. In this context, simulations in hyper-real-time are of high interest, as they would enable both comprehensive parameter scans and the study of slow processes, such as learning and long-term memory. Not even the fastest supercomputer available today is able to meet the challenge of accurate and reproducible simulation with hyper-real acceleration. The development of novel neuromorphic computer architectures holds out promise, but the high costs and long development cycles for application-specific hardware solutions makes it difficult to keep pace with the rapid developments in neuroscience. However, advances in System-on-Chip (SoC) device technology and tools are now providing interesting new design possibilities for application-specific implementations. Here, we present a novel hybrid software-hardware architecture approach for a neuromorphic compute node intended to work in a multi-node cluster configuration. The node design builds on the Xilinx Zynq-7000 SoC device architecture that combines a powerful programmable logic gate array (FPGA) and a dual-core ARM Cortex-A9 processor extension on a single chip. Our proposed architecture makes use of both and takes advantage of their tight coupling. We show that available SoC device technology can be used to build smaller neuromorphic computing clusters that enable hyper-real-time simulation of networks consisting of tens of thousands of neurons, and are thus capable of meeting the high demands for modeling and simulation in neuroscience.

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