Advances in multimodal MRI-based study of brain networks in patients with carotid artery stenosis / 中国辐射卫生

@#Stenosis and occlusion caused by carotid atherosclerosis is an important cause of ischemic stroke. In recent years, with the continuous development of magnetic resonance imaging (MRI) technology and the introduction of complex network theory, brain network analysis can be used not only to explain the clinical symptoms and cognitive dysfunction in patients with carotid stenosis caused by changes in network topological properties of different brain regions, but also to explore the imaging markers of carotid stenosis, thus providing important reference data for the diagnosis of early asymptomatic carotid stenosis, the selection of individualized intervention programs, and the assessment of efficacy. Brain network analysis has been used as a powerful tool. In this paper, we review the studies of structural and functional brain networks in patients with carotid stenosis, and introduce the definitions of brain network nodes and edges and important topological properties of complex networks. We also analyze the current research on brain network in patients with carotid stenosis, and discuss the challenges and outlook of existing imaging techniques and network construction methodologies in this field.

Abnormal topology of cortical thickness covariance network and altered functional connectivity in patients with anti-N-methyl-D-aspartate receptor encephalitis / 中华行为医学与脑科学杂志

Objective:To explore the changes in topological attributes of structural covariance network based on cortical thickness and the brain functional activities in patients with anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis by graph theory and functional connectivity (FC) analyses, and to investigate whether these changes were correlated to cognitive impairment.Methods:A total of 33 patients with anti-NMDAR encephalitis from Department of Neurology of the First Affiliated Hospital of Guangxi Medical University(patient group) and 35 healthy controls(control group) with matched gender, age, and education were included from July 2018 to November 2021.All subjects received cognitive function assessments, structural and functional magnetic resonance imaging scans.Structural covariance networks were constructed in the two groups based on cortical thickness values and topological characteristics of networks were computed.A non-parametric permutation test which repeated 1 000 times was used to compare the characteristics of the networks between the two groups.Brain regions with abnormal topology were defined as region of interest(ROI), and FC values in global brain level were calculated.SPM 12 and RESTplus were used to identify the brain regions with significant differences in FC values between the two groups.Finally, Spearman correlation analysis between FC values of significant brain regions and cognitive scores were performed by SPSS 24.0.Results:The cognitive score of patients with anti-NMDAR encephalitis (27.0(23.5, 28.0)) was lower than that in control group(29.0(27.0, 30.0)) ( Z=-3.029, P=0.002). Graph theory analysis found that the patients showed significantly increased clustering coefficients ( P=0.004) and decreased global efficiency ( P=0.004) compared with healthy controls.Moreover, the nodal efficiency of left ventral posterior cingulate cortex (vPCC) and right dorsal posterior cingulate cortex (dPCC), as well as the nodal degree centrality of left vPCC and left polar planum of superior temporal gyrus (ppSTG) in patient group were significantly decreased ( P<0.05, FDR corrected) compared with control group.FC analysis showed the increased FC values between left vPCC and posterior cerebellum (MNI: x=6, y=-66, z=-21), as well as between left ppSTG and anterior cerebellum (MNI: x=6, y=-54, z=-12) (GRF corrected, voxel level P<0.001, cluster level P<0.05) in patient grooup.The FC values between left vPCC and posterior cerebellum were negatively correlated with the cognitive scores ( r=-0.403, P=0.020). Conclusion:Patients with anti-NMDAR encephalitis show abnormal topology of structural covariance network based on cortical thickness and altered FC values, some of which are correlated to cognition and may be the underlying neural mechanism of cognitive impairment in patients with anti-NMDAR encephalitis.

The measurements of the similarity of dynamic brain functional network / 生物医学工程学杂志

Brain functional network changes over time along with the process of brain development, disease, and aging. However, most of the available measurements for evaluation of the difference (or similarity) between the individual brain functional networks are for charactering static networks, which do not work with the dynamic characteristics of the brain networks that typically involve a long-span and large-scale evolution over the time. The current study proposes an index for measuring the similarity of dynamic brain networks, named as dynamic network similarity (DNS). It measures the similarity by combining the "evolutional" and "structural" properties of the dynamic network. Four sets of simulated dynamic networks with different evolutional and structural properties (varying amplitude of changes, trend of changes, distribution of connectivity strength, range of connectivity strength) were generated to validate the performance of DNS. In addition, real world imaging datasets, acquired from 13 stroke patients who were treated by transcranial direct current stimulation (tDCS), were used to further validate the proposed method and compared with the traditional similarity measurements that were developed for static network similarity. The results showed that DNS was significantly correlated with the varying amplitude of changes, trend of changes, distribution of connectivity strength and range of connectivity strength of the dynamic networks. DNS was able to appropriately measure the significant similarity of the dynamics of network changes over the time for the patients before and after the tDCS treatments. However, the traditional methods failed, which showed significantly differences between the data before and after the tDCS treatments. The experiment results demonstrate that DNS may robustly measure the similarity of evolutional and structural properties of dynamic networks. The new method appears to be superior to the traditional methods in that the new one is capable of assessing the temporal similarity of dynamic functional imaging data.

A graph-theory-based method for processing of currency metabolites in metabolic networks / 生物工程学报

Graph-theory-based pathway analysis is a commonly used method for pathway searching in genome-scale metabolic networks. However, such searching often results in many pathways biologically infeasible due to the presence of currency metabolites (e.g. H+, H2O, CO2, ATP etc.). Several methods have been proposed to address the problem but up to now there is no well-recognized methods for processing the currency metabolites. In this study, we proposed a new method based on the function of currency metabolites for transferring of functional groups such as phosphate. We processed most currency metabolites as pairs rather than individual metabolites, and ranked the pairs based on their importance in transferring functional groups, in order to make sure at least one main metabolite link exists for any reaction. The whole process can be done automatically by programming. Comparison with existing approaches indicates that more biologically infeasible pathways were removed by our method and the calculated pathways were more reliable, which may facilitate the graph-theory-based pathway design and visualization.

The topology of resting-state functional networks in the brain after an ischemic stroke / 中华物理医学与康复杂志

Objective:To explore any changes in the topology of the brain′s resting-state functional networks after an ischemic stroke causing cognitive impairment (iPSCI) and their relationship with the impairment.Methods:Twenty-one patients with impaired cognition after a stroke were recruited into an iPSCI group, and 21 healthy counterparts matched in gender, age and the education level formed the control (HC) group. Three-dimensional T1-weighted anatomical images and resting state functional magnetic resonance images of all of the subjects were collected and any differences in brain network topology were analyzed using graph theory. The degree of centrality (DC), between centrality (BC) and the global topological properties of each brain region were compared using independent-sample t-tests. Spearman correlation coefficients were computed to analyze the significance of any correlation between topology differences and Montreal Cognitive Assessment Scale (MoCA) or Mini-Mental Status Examination (MMSE) scores.Results:Compared with the HC group, a significant DC increase was observed in the orbital part of the right of middle frontal gyrus (ORBmid.R), the right hippocampus (HIP.R), and the right thalamus (THA.R). There was a significant decrease in the left Rolandic operculum (ROL.L), the left postcentral gyrus (PoCG.L), the left supramarginal gyrus (SMG.L), the left angular gyrus (ANG.L), the left and right caudate nucleus (CAU.L and CAU.R), the putamen of the left lenticular nucleus (PUT.L), the left Heschl gyrus (HES.L), the left superior temporal gyrus (STG.L), and the temporal pole of the left superior temporal gyrus (TPOsup.L). Compared with the HC group, the brain regions of the iPSCI group in which the BC had increased significantly were the orbital part of the left middle frontal gyrus (ORBmid.L), the left cuneus (CUN.L), and the right precuneus (PCUN.R). DC was significantly decreased in the left caudate nucleus (CAU.L), the left temporal pole of the superior temporal gyrus (TPOsup.L), and the left of inferior temporal gyrus (ITG.L). Compared with the HC group, the area under the receiver operating curve (AUC) of the shortest path length (Lp) and the normalized Lp (λ) of the iPSCI group increased significantly, and the AUC of the normalized clustering coefficient (γ) and small-worldness (σ) decreased significantly. The DCs of the ROL.L, PoCG.L, CAU.L, HES.L, STG.L and TPOsup.L regions showed moderate positive correlation with the MoCA and MMSE scores ( r>0.4), as did the BC of the CAU.L and TPOsup.L regions ( r>0.4). Conclusions:Cognitive impairment is mainly associated with decreased nodal properties in the brain regions related to language and in the caudate nucleus. The topology of the frontal lobe, hippocampus, thalamus, striatum and default networks may self-repair after an iPSCI. The brain′s functional network after an iPSCI still has small-world properties, but with low efficiency and high cost.

Network analysis of the variables involved in career development / Análise de rede das variáveis envolvidas no desenvolvimento de carreira / Análisis de red de las variables involucradas en el desarrollo profesional

The aim of the study was to identify the relationships between career commitment and the perception of employability, career adaptability, self-reflection and insight of professionals from the southern region of Brazil. Participants were 535 individuals who answered an online questionnaire with sociodemographic questions and scales from career commitment, employability perception, career adaptability, self-reflection and insight, to evaluate the variables of interest in the study. The data were submitted to descriptive and network analysis. The results show a moderate and positive relationship between the variables studied and highlight the centrality and strength of the variables identity, planning and confidence among the analyzed variables. It is concluded that it is essential to encourage professionals to reflect on professional choices and their responsibility with their careers, based on the promotion of self-knowledge. Also, the role of organizations in the development of People Management practices that promote autonomy and relationships of trust stands out. (AU)

O objetivo do estudo foi identificar as relações entre comprometimento com a carreira e percepção de empregabilidade, adaptabilidade de carreira, autorreflexão e insight de profissionais da região Sul do Brasil. Participaram 535 indivíduos que responderam a um questionário on-line com questões sociodemográficas e escalas de comprometimento de carreira, percepção de empregabilidade, adaptabilidade de carreira, autorreflexão e insight, para avaliar as variáveis de interesse do estudo. Os dados foram submetidos a análises descritivas e de rede. Os resultados evidenciam relação moderada e positiva entre as variáveis pesquisadas e destacam a centralidade e força das variáveis Identidade, Planejamento e Confiança, entre as variáveis analisadas. Conclui-se que é fundamental estimular profissionais a refletir sobre escolhas profissionais e a sua responsabilidade com a carreira, a partir da promoção do autoconhecimento. Também, destaca-se o papel das organizações no desenvolvimento de práticas de Gestão de Pessoas que promovam autonomia e relações de confiança. (AU)

El objetivo del estudio fue identificar las relaciones entre el compromiso profesional y la percepción de empleabilidad, la adaptabilidad profesional, la autorreflexión y el insight de profesionales de la región sur de Brasil. Participaron 535 individuos que respondieron un cuestionario online con preguntas sociodemográficas y escalas compromiso profesional; percepción de empleabilidad; adaptabilidad profesional; autorreflexión e insight, para evaluar las variables de interés del estudio. Los datos fueron sometidos a análisis descriptivos y de red. Los resultados evidencian una relación moderada y positiva entre las variables investigadas y destacan la centralidad y fuerza de las variables identidad, planificación y confianza, entre las variables analizadas. Se concluye que es fundamental incentivar a los profesionales a reflexionar sobre elecciones profesionales y su responsabilidad con la carrera, a partir de la promoción del autoconocimiento. Asimismo, se destaca el papel de las organizaciones en el desarrollo de prácticas de Gestión de Personas que promuevan autonomía y relaciones de confianza. (AU)

Alterations of brain functional complex network in temporal lobe epilepsy patients: a functional magnetic resonance imaging study / 中华神经科杂志

Objective:To investigate longitudinal alterations of brain functional complex network by rest-stage functional magnetic resonance imaging (rs-fMRI) and graph theory in patients with temporal lobe epilepsy (TLE).Methods:A total of 13 TLE patients (TLE baseline group) and 13 healthy controls (healthy control group) were enrolled to observe alterations in complex functional network. The subjects were recruited in the Epilepsy Clinic of the First Affiliated Hospital of Guangxi Medical University from January 2015 to April 2018. For longitudinal analysis, TLE patients were followed-up for three years (TLE follow-up group). All participants underwent rs-fMRI and attention network test (ANT). Finally, a cross-sectional study was conducted by comparing the area under the curve (AUC) between the TLE baseline group and the healthy control group, and a longitudinal analysis was conducted by comparing the AUC between the TLE baseline group and the TLE follow-up group.Results:Cross-sectional analysis showed that the alerting function of the TLE baseline group was declined [The tonic alertness reaction time, phasic alertness reaction time and alertness were (727.00±126.07) ms, (692.85±132.37) ms, and (34.15±23.50) ms, respectively in the TLE baseline group, which were (639.87±81.41) ms, (589.50±80.59) ms, and (50.37±14.71) ms, respectively in the healthy control group, with statistically significant differences between the two groups ( t=-2.09, P=0.047; t=-2.41, P=0.024; t=2.11, P=0.045)]; the TLE baseline group demonstrated decreased clustering coefficient in left supplementary motor area (SMA.L)(AUC was 0.162±0.044, 0.189±0.021, respectively; t=-4.14, P=4.67E-04) and left inferior parietal supramarginal angular gyri (AUC was 0.178±0.021, 0.202±0.026, respectively; t=-2.42, P=0.024), and decreased nodal local efficiency in SMA.L (AUC was 0.239±0.045, 0.260±0.022, respectively; t=-4.13, P=4.77E-04) and left inferior temporal gyrus (AUC was 0.233±0.036, 0.253±0.027, respectively; t=-3.03, P=0.006) compared with the healthy control group, and both SMA.L clustering coefficient and nodal local efficiency were positively correlated with TLE patients′ duration ( r=0.652, P<0.05; r=0.611, P<0.05). Longitudinal analysis showed that the global network efficiency of the TLE follow-up group decreased (The AUC of the TLE baseline group was 0.182±0.008, and the AUC of the TLE follow-up group was 0.169±0.015, t=2.73, P=0.017), which was negatively correlated with alertness ( r=-0.617, P<0.05). Conclusions:TLE patients show impairment of topological properties of brain functional network. SMA.L is a significant node in network. Alterations of brain functional network associate with duration. The decline in global network efficiency may be a characteristic of progressive deficit to TLE.

Changes in brain structural network connection of children with attention deficit hyperactivity disorder / 中华实用儿科临床杂志

Objective@#To explore the changes in brain structure network connection in children with attention deficit hyperactivity disorder(ADHD), and to provide novel markers for early identification of ADHD in clinical practice.@*Methods@#Deterministic diffusion-tensor tractography and graph theory approaches were used to investigate the topologic organization of the brain structural connectome in 25 children with ADHD and 23 healthy control children from May 2017 to May 2018, at Children′s Hospital of Xuzhou Medical University.Individual white matter networks were constructed for each participant, then the global properties, nodal properties and edge-wise distributions were compared between the two groups.@*Results@#(1)The global efficiency of the ADHD group (0.30±0.13) was significantly lower than that of the healthy control group (0.38±0.11), but the clustering coefficient (0.35±0.28) and the characteristic path length (2.94±0.38) were significantly higher than those of the healthy control group (0.28±0.10, 2.65±0.37), and the differences were statistically significant (t=-2.41, 2.31, 2.62, all P<0.05). (2)In the ADHD group, the nodal efficiency of the left inferior frontal gyrus, triangular part (0.13±0.06), left supramarginal gyrus (0.30±0.10), left inferior parietal, angular gyri (0.29±0.10), left precuneus (0.26±0.12)were significantly lower than the healthy control group(0.17±0.07, 0.38±0.10, 0.40±0.12, 0.35±0.12), while the nodal efficiency of the right superior frontal gyrus, orbital part and right paracentral lobule were significantly higher than the healthy control group(0.49±0.17, 0.43±0.14), and the differences were statistically significant[t=-2.52, -2.62, -3.11, -2.77, 2.34, 2.79, all P<0.05, false discovery rate(FDR) corrected]. (3)A disrupted subnetwork was observed that consisted of left frontoparietal areas, basal ganglia, thalamus and insular network (P<0.05, FDR corrected), which has the potential to discriminate individuals with ADHD from healthy control children(area under receiver operating characteristic curve was 0.78). (4)Diminished strength of the subnet work connections was correlated with the attention defect in patients with ADHD(r=-0.607, P=0.003).@*Conclusions@#Using magnetic resonance diffusion tensor imaging, with the help of graph theory analysis technology, ADHD children can be observed changes in brain structure network at multiple levels.The distribution pattern of brain network structure connection changes is expected to become a new marker for identifying ADHD.

Independent Component Analysis and Graph Theoretical Analysis in Patients with Narcolepsy / 神经科学通报·英文版

The present study was aimed to evaluate resting-state functional connectivity and topological properties of brain networks in narcolepsy patients compared with healthy controls. Resting-state fMRI was performed in 26 adult narcolepsy patients and 30 matched healthy controls. MRI data were first analyzed by group independent component analysis, then a graph theoretical method was applied to evaluate the topological properties in the whole brain. Small-world network parameters and nodal topological properties were measured. Altered topological properties in brain areas between groups were selected as region-of-interest seeds, then the functional connectivity among these seeds was compared between groups. Partial correlation analysis was performed to evaluate the relationship between the severity of sleepiness and functional connectivity or topological properties in the narcolepsy patients. Twenty-one independent components out of 48 were obtained. Compared with healthy controls, the narcolepsy patients exhibited significantly decreased functional connectivity within the executive and salience networks, along with increased functional connectivity in the bilateral frontal lobes within the executive network. There were no differences in small-world network properties between patients and controls. The altered brain areas in nodal topological properties between groups were mainly in the inferior frontal cortex, basal ganglia, anterior cingulate, sensory cortex, supplementary motor cortex, and visual cortex. In the partial correlation analysis, nodal topological properties in the putamen, anterior cingulate, and sensory cortex as well as functional connectivity between these regions were correlated with the severity of sleepiness (sleep latency, REM sleep latency, and Epworth sleepiness score) among narcolepsy patients. Altered connectivity within the executive and salience networks was found in narcolepsy patients. Functional connection changes between the left frontal cortex and left caudate nucleus may be one of the parameters describing the severity of narcolepsy. Changes in the nodal topological properties in the left putamen and left posterior cingulate, changes in functional connectivity between the left supplementary motor area and right occipital as well as in functional connectivity between the left anterior cingulate gyrus and bilateral postcentral gyrus can be considered as a specific indicator for evaluating the severity of narcolepsy.

Brain structural network changes in Parkinson's disease with mild cognitive impairment:a diffusion tensor imaging study / 中华行为医学与脑科学杂志

Objective To explore the changes of brain structure network in patients with Parkinson's disease with mild cognitive impairment(PD-MCI),and to provide novel markers for the early recognition of PD-MCI. Methods Total 47 patients with primary PD were continuously enrolled at the De-partment of Neurology,Affiliated Hospital of Xuzhou Medical University from May 2017 to May 2018. Twenty-four healthy volunteers were selected as the healthy control (HC) group. General demographic data were col-lected from all subjects. The overall cognitive function and the five cognitive domains (attention and working memory,executive function,language,memory and visual spatial function) were comprehensively evaluated, then the patients with PD were further divided into PD-MCI group(n=22) and PD-NC group(n=25) based on their cognitive evaluation results. All subjects completed the diffusion tensor imaging( DTI) scan and the individual structural brain connection was obtained by deterministic diffusion-tensor tractography. By graph theory analysis technology,the network properties (global properties and node properties) and edge-wise dis- tributions were compared to assess structural connectivity differences among the three groups. Results Com-pared with the PD-NC and HC groups,the PD-MCI group had a larger characteristic path length(PD-NC:(8. 33±0. 95),HC:(8. 18±1. 35),PD-MCI:(9. 20±1. 52),F=4. 14,P<0. 05) and reduced global efficien-cy (PD-NC:(0. 13±0. 05),HC:(0. 13±0. 04),PD-MCI:(0. 10±0. 04),F=3. 73,P<0. 05) in addition to a lower nodal efficiency in frontoparietal areas,thalamus,cingulate gyrus,and insular(P=0 . 003-0. 040,FDR correction). Compared with the HC group,the PD-MCI group had a large frontotemporoparietal areas,basal ganglia,and insular network with decreased connection strength (P<0. 05,FDR correction). Compared with the PD-NC group,the PD-MCI group had a lower network connection strength in the frontoparietal areas (P<0. 05,FDR correction). Conclusion A disruption of structural connections that make up the brain network can lead to changes in information integration and delivery,leading to cognitive dysfunction in patients with PD. The distribution pattern of brain network structure connection changes is expected to become a new marker for identifying PD-MCI.

VisConnectome: an independent and graph-theory based software for visualizing the human brain connectome / 生物医学工程学杂志

As a complex system, the topology of human's brain network has an important effect on further study of brain's structural and functional mechanism. Graph theory, a kind of sophisticated analytic strategies, is widely used for analyzing complex brain networks effectively and comparing difference of topological structure alteration in normal development and pathological condition. For the purpose of using this analysis methodology efficiently, it is necessary to develop graph-based visualization software. Thus, we developed VisConnectome, which displays analysis results of the brain network friendly and intuitively. It provides an original graphical user interface (GUI) including the tool window, tool bar and innovative double slider filter, brain region bar, runs in any Windows operating system and doesn't rely on any platform such as Matlab. When importing the user-defined script file that initializes the brain network, VisConnectome abstracts the brain network to the ball-and-stick model and render it. VisConnectome allows a series of visual operations, such as identifying nodes and connection, modifying properties of nodes and connection such as color and size with the color palette and size double slider, imaging the brain regions, filtering the brain network according to its size property in a specific domain as simplification and blending with the brain surface as a context of the brain network. Through experiment and analysis, we conclude that VisConnectome is an effective visualization software with high speed and quality, which helps researchers to visualize and compare the structural and functional brain networks flexibly.

Altered Functional Brain Networks in Patients with Traumatic Anosmia: Resting-State Functional MRI Based on Graph Theoretical Analysis

OBJECTIVE: Traumatic anosmia is a common disorder following head injury; however, little is known regarding its neural basis and influence on the functional networks. Therefore, we aimed to investigate the functional connectivity changes in patients with traumatic anosmia compared to healthy controls using resting-state functional magnetic resonance imaging (rs-fMRI). MATERIALS AND METHODS: Sixteen patients with traumatic anosmia and 12 healthy controls underwent rs-fMRI. Differences in the connectivity of the olfactory and whole brain networks were compared between the two groups. Graph theoretical parameters, such as modularity and global efficiency of the whole brain or olfactory networks, were calculated and compared. Correlation analyses were performed between the parameters and disease severity. RESULTS: Patients with traumatic anosmia showed decreased intra-network connectivity in the olfactory network (false discovery rate [FDR]-corrected p < 0.05) compared with that in healthy controls. Furthermore, the inter-network connectivity was increased in both the olfactory (FDR-corrected p < 0.05) and whole brain networks (degree-based statistic-corrected p < 0.05) in the anosmia group. The whole brain networks showed decreased modularity (p < 0.001) and increased global efficiency (p = 0.019) in patients with traumatic anosmia. The modularity and global efficiency were correlated with disease severity in patients with anosmia (p < 0.001 and p = 0.002, respectively). CONCLUSION: Traumatic anosmia increased the inter-network connectivity observed with rs-fMRI in the olfactory and global brain functional networks. rs-fMRI parameters may serve as potential biomarkers for traumatic anosmia by revealing a more widespread functional damage than previously expected.

Modelación con teoría de grafos para la unidimensionalidad de un instrumento de evaluación / Modeling with graph theory to unidimensionality for an assessment instrument

En el marco de las políticas públicas en Colombia sobre calidad de la educación superior se encuentran los lineamientos para que el Estado reconozca los programas de pregrado como de alta calidad, entre tales lineamientos se consideran los sistemas de evaluación de los estudiantes basados en políticas institucionales claras y transparentes que propicien una identificación integral de las condiciones académicas y actitudinales de los estudiantes por lo que es imprescindible tecnificar y modernizar los procesos de evaluación para fortalecer la emisión de inferencias confiables sobre el logro académico. En este artículo se describe una aplicación de la Teoría de Grafos usando algunas de sus definiciones y teoremas básicos con la intención de potenciar su uso para el estudio del supuesto de unidimensionalidad de la Teoría de Respuesta al Ítem como alternativa para robustecer la evaluación. La unidimensional fue entendida en el sentido de la homogeneidad escalar y de criterio para las relaciones de orden definidas por la dominación tanto para ítems como para evaluados: para los ítems conforme al número de evaluados que los contestaron correctamente y a la dificultad; para los evaluados respecto al número de respuestas correctas y a la habilidad. Se aplicó la combinación de las dos teorías a un caso de estudio que contempla el instrumento de la prueba diagnóstica del Examen de Clasificación de Matemáticas Básicas en la Universidad Jorge Tadeo Lozano, con esto se ofrece un valor agregado porque se evidencian los resultados de forma algorítmica y visual con ayuda de herramientas informáticas especializadas.

In Colombia, public policies about quality of higher education involve student assessment systems as a relevant characteristic. These systems should have clear and transparent institutional policies requiring comprehensive identification of attitudinal and academic conditions about examinee performance. Consequently, on the way of continuous improvement of academic services offered by institutions of higher education, an assessment process adequately technified allowing valid inferences about academic achievement is required. In this sense, the Rasch measurement model of Item Response Theory is a modern alternative to strengthen educational measurement estimating the ability of the student and the difficulty of the item on a comparable scale. Unidimensionality, local independence and internal consistency are assumptions made in Rasch measurement model. Unidimensionality assumption has several definitions, one of them is the occurrence of a dominant factor influencing test performance. Another definition is considered in the present study. Here, unidimensionality was interpreted as scalar and criterial homogeneity for the order relations defined by domination for items and assessed applicants. Graph Theory is an ideal mathematical modelling approach to this assumption inasmuch as represent intangible interactions as required. In order to achieve this, Graph Theory and Item Response Theory were combined to examine the qualifying test for the Basic Mathematics subject at Jorge Tadeo Lozano University as a case study. This test was composed by 45 items divided in three blocks. With several combinations of these blocks, three virtual booklets were obtained each one comprising 30 of them. From the application of June 2011, a test sample of 509 responses chains was obtained. Three data bases were processed one for each booklet, the first spanned 175 responses chains, the second 170 and the third one 164. To begin with the exmination on the Rasch measurement model, the parameters reliability, separation, Cronbach Alpha and item residual correlation were estimated to gauge and determine performance test for getting acceptable values in each booklet applied. Tatsuoka was followed to undertake the path to unidimensionality from Graph Theory gathering a real case experience processed with suitable software. Additionally, the sensitivity of the order relation was verified through: 1) ordering by number of correct responses per item (1I order) and items difficulty (2I order); 2) ordering by number of correct responses per applicant (1E order) and estimated ability (2E order). Furthermore, the linear models were obtained collating these orders. In like manner, three Guttman scales and their adjacency matrices were schematized one for each booklet. Subsequently, the respective graphs were processed and represented using Gephi just as a specialized tool that enables running some algorithms like Force Atlas. Afterwards, the second power of each adjacency matrix was found using Matlab 2014b and domination matrices were calculated for both items and applicants in the aforementioned orders for a total of 12 matrices. Consistency index developed by Cliff was computed for the domination matrices. As a result, moderate consistency was observed. Significant domination for the entries of these matrices was analyzed through McNemar test in order to have an asymmetric dominance relation. Moreover, a reachable matrix was calculated for each one of these significant domination matrices as a limit ofa sequence of boolean powers. Finally, dominance hierarchies were illustrated with vertex degrees and compared with student maps by the means of Winsteps 3.73. The combination of Graph Theory and Item Response Theory allowed a deeper comprehension of unidimensionality assumption. Thereupon, universities can optimize their resources offering to applicant differential academic options per individual position in the ability scale. The results can be used to outline advantages for the applicants who can evidence their position in the ability scale and identify the different areas to improve.

Análisis electroencefalográfico de la conectividad funcional en habituación por teoría de gráficas / Electroencephalographic analysis of the functional conectivity in habituation by graphics theory

Resumen Se ha propuesto, en la literatura de neurociencias, la hipótesis de que el cerebro funciona con base en redes glioneuronales, responsables de los procesos sensoriales, motores y cognitivos. La teoría de gráficas ofrece modelos matemáticos para describir estas redes complejas a partir de simples abstracciones: nodos y aristas. En este trabajo se plantea el uso de técnicas de procesamiento de señales para el análisis de la conectividad funcional entre ensambles neuronales a partir de medidas derivadas del EEG a través de la teoría de gráficas. Se describen los procedimientos para el análisis de la conectividad, desde el procesamiento y acondicionamiento de los registros, el cálculo de la densidad espectral en el EEG en banda ancha, la determinación de medidas de conectividad entre electrodos, y la estimación de parámetros de las redes complejas resultantes. Se analizó el EEG de 50 sujetos en intervalos de antes (Pre) y durante la fotoestimulación repetida (Rph). Con base en la significancia estadística de la respuesta durante Rph de desincronización/sincronización (D/S) en la banda alfa, y su extensión en las regiones corticales, los participantes se separaron en tres grupos: G1, G2 y G3. La pendiente de la regresión lineal D/S vs repetición en banda alfa, fue significativa en 16 de 16 regiones en G1, 12 de 16 en G2 y 5 de 16 en G3. La conectividad funcional siguió estos cambios mientras que en las bandas delta, theta y beta no se registraron modificaciones. D se relaciona con activación y la S con inhibición lo que apoya la hipótesis de la participación de alfa en el proceso cognitivo de habituación a la fotoestimulación.

Abstract The hypothesis that the brain works using glial-neuronal networks that are responsible for sensory, motor and cognitive processes has been proposed in the neuroscience literature. Graph theory offers mathematical models to describe these complex networks from simple abstractions such as nodes and connecting edges. In this work, usign signal processing techniques to the analysis of functional connectivity between neuronal emsembles derived from EEG measurements through theory graph. Procedures for the analysis of connectivity are described, from multichannel record processing and conditioning, computation of wideband power spectral density, determination of connectivity measures between electrodes, and parameter estimation of the resulting complex networks. EEG recordings from fifty subjects were analyzed in intervals before (pre) and during repeated photostimulation (Rph). Based on the statistical significance of the response during Rph, desynchronization/synchronization (D/S) in alfa band, and its wide distribution in corticals areas, the participants were divided into three groups: G1 , G2 and G3. The slope D/S in alfa band was significant in 16 of 16 regions (G1), 12 of 16 (G2) and 5 of 16 (G3). The functional connectivity depicted the same trend as these changes, whereas in the delta, theta and beta bands occurred no modifications. D is related to activation and S with inhibition, supporting the hypothesis of alfa-band's participation in the cognitive process of habituation to photostimulation.

Conectividad funcional en adultos mayores a partir de resonanciamagnética funcional como un posible indicador para la enfermedad deAlzheimer / Functional connectivity in senior adults from fMRI as a possible indicator for Alzheimer’s Disease

La enfermedad de Alzheimer es una enfermedad neurodegenerativa y la causa de demenciamás frecuente en el mundo. Esta enfermedad se caracteriza por muerte neuronal que lleva a una pérdida deconectividad cerebral general. Técnicas como la conectividad funcional a partir de imágenes de resonanciamagnética pueden brindar información acerca de la interacción entre regiones cerebrales y, por tanto, puedeser un indicador del Alzheimer.Objetivo: evaluar la conectividad funcional a partir de imágenes de resonancia magnética funcional en estadode reposo en adultos mayores como posible biomarcador para la enfermedad de Alzheimer.Materiales y métodos: en una población de 35 sujetos de edad avanzada (10 pacientes con Alzheimer de75 ± 2,87 años, 10 pacientes con deterioro cognitivo leve de 74,9 ± 2,88 años, y 15 personas sanas de 75,35 ±2,91 años), se compararon las redes de conectividad funcional obtenidas a través de la correlación temporal dela señal BOLD y elementos de la teoría de grafos. Se calcularon las medidas de las redes (costo y grado medio),y se correlacionaron estas medidas con las escalas neuropsicológicas ADNI-mem y ADAS-Cog.Resultados: en los pacientes con Alzheimer hay una disminución de la conectividad en comparación con loscontroles sanos y los pacientes con deterioro cognitivo leve. Se encontró una correlación significativa entre elcosto de las redes en los sujetos sanos y las escalas neuropsicológicas.Conclusión: se confirma la desconexión existente en la enfermedad de Alzheimer y se muestra que la alteraciónde la actividad cerebral en el deterioro cognitivo y Alzheimer se puede medir mediante el algoritmo basado engrafos desarrollado en este trabajo...

Alzheimer’s disease is a neurodegenerative disease and the most common cause of dementiain the world. This disease is characterized by neuronal cell death leading to an overall loss of brain connectivity.Functional connectivity from magnetic resonance images can provide information about the interactionbetween brain regions and therefore may be an indicator of Alzheimer. Objective: assessing functional connectivity from functional magnetic resonance images at rest in elderly asa potential biomarker for Alzheimer’s disease.Materials and methods: in a population of 35 elderly subjects (10 patients with Alzheimer 75 ± 2,87 years,10 patients with mild cognitive impairment 74,9 ± 2,88 years and 15 healthy individuals 75,35 ± 2,91years),functional connectivity networks obtained through the temporal correlation of BOLD signal and elementsof the graph theory were compared. Network indexes (cost and average degree) were calculated, and furthercorrelated with the neuropsychological scales, ADNI-mem, and ADAS-Cog...

Graph analysis of semantic word association among children, adults, and the elderly / Análise de grafos de associação semântica de palavras entre crianças, adultos e idosos

This study used graph analysis to investigate how age differences modify the structure of semantic word association networks of children and adults and if the networks present a small-world structure and a scale-free distribution which are typical of natural languages. Three age groups of Brazilian Portuguese speakers (children, adults and elderly people) participated in the experiment. Quantitative and qualitative measures suggested that adults and elderly speakers have similar network structures. Children's network showed fewer nodes, connections and clusters, and longer inter-node distances. All networks presented a small-world structure, but they did not show entirely scale-free distributions. These results suggest that from childhood to adulthood, there is an increase not only in the number of words semantically linked to a target but also an increase in the connectivity of the network.

Este estudo utilizou análise de grafos para investigar como a idade modifica a estrutura das redes de associações semânticas de palavras de crianças e adultos e se estas redes apresentam estrutura small-world e distribuição scale-free típicas de linguagens naturais. Participaram dos experimentos três grupos etários (crianças, adultos e idosos) falantes do Português Brasileiro. Medidas quantitativas e qualitativas sugeriram que adultos e idosos possuem redes semelhantes quanto a número de nós, conexões e agrupamentos. A rede das crianças expressou menor número de nós, conexões e agrupamentos e maiores distancias inter-nós. As redes apresentaram uma estrutura small-world, mas não uma distribuição scale-free completa. Os resultados sugerem que além do número de palavras semanticamente associadas aos alvos aumentar das crianças para os adultos, as redes se tornaram mais conectadas.

Análisis topológico del interactoma de Helicobacter pylori revela proteínas topológicamente esenciales: identificación de blancos terapéuticos / Topological analysis of the interactome of Helicobacter pylori reveals topologically essential proteins: identification of therapeutic targets

La Helicobacter pylori ha colonizado la mitad de la población mundial; su infección presenta una prevalencia del 70% al 90% en países en vía de desarrollo y del 25% al 50% en países industrializados. Está establecido que la infección se asocia con el desarrollo de gastritis crónica, úlcera gástrica y duodenal y con cáncer de estómago en el humano. Helicobacter pylori fue la primera bacteria patógena para la cual se dedujo el interactoma y por análisis topológicos se identificaron 702 proteínas involucradas en 1359 interacciones con una cobertura del 97,7% con escala libre; es decir, que el interactoma contiene proteínas topológicamente esenciales. Sin embargo, dichas proteínas y sus asociaciones fisiológicas no han sido descritas, perdiendo de esta manera la posibilidad de identificar posibles blancos terapéuticos. Con el objetivo de identificar proteínas topológicamente esenciales se realizó una reconstrucción del interactoma de la cepa H. pylori ATCC 26695 empleando los complementos BioNetBuilder y NetworkAnalyzer de Cytoscape y la aplicación web cytoHubba. La reconstrucción presentó 896 proteínas y 2416 interacciones con una cobertura del 96% del proteoma ajustada a la distribución de ley de potencias, es decir, presentó escala libre. Usando NetworkAnalyzer y la aplicación Hubba se identificaron proteínas esenciales según los parámetros K y BC; con las que se construyó una subred. El análisis de esta subred mostró que el sistema de secreción tipo IV interactúa con subsistemas metabólicos de lípidos, aminoácidos y ácidos nucleicos por medio de proteínas, para las cuales esta interacción no había sido sugerida. Además, estas interacciones son explicables por perfiles de expresión dependientes del pH, adhesión y homeostasis del hierro; lo cual permite complementar tanto la biología básica de la cepa como postular nuevos blancos terapéuticos putativos.

Mathematical modeling for selecting center locations for medical and health supplies reserve in Hainan Province

OBJECTIVE@#To explore how to choose the center locations to build the medical and health supplies reserve among many island towns.@*METHODS@#The center locations were selected from 18 towns Hainan Province, it's maximum service range (distance) was required to reach the minimum, or to minimize.@*RESULTS@#Three scenarios were considered, the center locations included only one town, two towns, three towns. By the use of graph theory and MATLAB programming, a mathematical model was established to obtain the shortest distance and the shortest path between arbitrary two towns.@*CONCLUSIONS@#We find out the center sites under certain conditions, and determine the specific service ranges of the center sites.

Network models in the study of metabolism

The systematic study of the genetic fingerprint (genomics) and the biochemistry (metabolites) that goes with a specific cellular process requires the characterization of all the small molecules that form the profile of metabolites and the associated genes. The metabolome represents the collection of all the metabolites during certain process in an organism. The transcriptome represents the gene expression profile, all the messengers RNA in a defined condition. Then to understand the whole process, the studies of metabolites must be accompanied with studies of the gene expression, hence the metabolome must be accompanied by the transcriptome, so we can identify genes and metabolites whose synthesis is induced by a specific process, an infection or stress. Studies of metabolomics generate an enormous amount of data, then they need mathematical and computational tools to establish the correlations between the biochemical and genetic data, and to build up networks that represent the complex metabolic interactions that occur in each case, using tools like Graph and Networks Theory to elucidate the emergent properties inherent to the complex interactions of the metabolic maps. This paper describes the major mathematical tools that can be used for these studies, with emphasis on a semi-qualitative proposal known as the kinetic structural model.