Connectivity Analysis in EEG Data: A Tutorial Review of the State of the Art and Emerging Trends

Understanding how different areas of the human brain communicate with each other is a crucial issue in neuroscience. The concepts of structural, functional and effective connectivity have been widely exploited to describe the human connectome, consisting of brain networks, their structural connections and functional interactions. Despite high-spatial-resolution imaging techniques such as functional magnetic resonance imaging (fMRI) being widely used to map this complex network of multiple interactions, electroencephalographic (EEG) recordings claim high temporal resolution and are thus perfectly suitable to describe either spatially distributed and temporally dynamic patterns of neural activation and connectivity. In this work, we provide a technical account and a categorization of the most-used data-driven approaches to assess brain-functional connectivity, intended as the study of the statistical dependencies between the recorded EEG signals. Different pairwise and multivariate, as well as directed and non-directed connectivity metrics are discussed with a pros-cons approach, in the time, frequency, and information-theoretic domains. The establishment of conceptual and mathematical relationships between metrics from these three frameworks, and the discussion of novel methodological approaches, will allow the reader to go deep into the problem of inferring functional connectivity in complex networks. Furthermore, emerging trends for the description of extended forms of connectivity (e.g., high-order interactions) are also discussed, along with graph-theory tools exploring the topological properties of the network of connections provided by the proposed metrics. Applications to EEG data are reviewed. In addition, the importance of source localization, and the impacts of signal acquisition and pre-processing techniques (e.g., filtering, source localization, and artifact rejection) on the connectivity estimates are recognized and discussed. By going through this review, the reader could delve deeply into the entire process of EEG pre-processing and analysis for the study of brain functional connectivity and learning, thereby exploiting novel methodologies and approaches to the problem of inferring connectivity within complex networks

Transfer Entropy Analysis of Pulse Arrival Time - Heart Period Interactions during Physiological Stress

Although Heart Period (HP) variability is the most widely used measure to assess cardiovascular oscillations, its evaluation combined with that of Pulse Arrival Time (PAT) variability may provide additional information about cardiac dynamics and cardiovascular interactions. In this study, we computed the transfer entropy from PAT to HP in 76 subjects monitored at rest and during orthostatic and mental stress using both a model-free (k- Nearest Neighbors) and a linear parametric estimator. Our results show how the information flow between these two variables depends on the physiological condition and how the nonlinear measure captures more information than the linear one during orthostatic stress

Spectral analysis of the beat-to-beat variability of arterial compliance

Arterial compliance is an important parameter influencing ventricular-arterial coupling, depending on structural and functional mechanics of arteries. In this study, the spontaneous beat-to-beat variability of arterial compliance was investigated in time and frequency domains in thirty-nine young and healthy subjects monitored in the supine resting state and during head-up tilt. Spectral decomposition was applied to retrieve the spectral content of the time series associated to low (LF) and high frequency (HF) oscillatory components. Our results highlight: (i) a decrease of arterial compliance with tilt, in agreement with previous studies; (ii) an increase of the LF power content concurrent with a decrease of the HF power, potentially reflecting changes in vasomotor tone, blood pressure and heart rate variability associated with higher sympathetic activity and vagal withdrawal occurring with tilt

Comparison of discretization strategies for the model-free information-theoretic assessment of short-term physiological interactions

This work presents a comparison between different approaches for the model-free estimation of information-theoretic measures of the dynamic coupling between short realizations of random processes. The measures considered are the mutual information rate (MIR) between two random processes X and Y and the terms of its decomposition evidencing either the individual entropy rates of X and Y and their joint entropy rate, or the transfer entropies from X to Y and from Y to X and the instantaneous information shared by X and Y. All measures are estimated through discretization of the random variables forming the processes, performed either via uniform quantization (binning approach) or rank ordering (permutation approach). The binning and permutation approaches are compared on simulations of two coupled non-identical Hènon systems and on three datasets, including short realizations of cardiorespiratory (CR, heart period and respiration flow), cardiovascular (CV, heart period and systolic arterial pressure), and cerebrovascular (CB, mean arterial pressure and cerebral blood flow velocity) measured in different physiological conditions, i.e., spontaneous vs paced breathing or supine vs upright positions. Our results show that, with careful selection of the estimation parameters (i.e., the embedding dimension and the number of quantization levels for the binning approach), meaningful patterns of the MIR and of its components can be achieved in the analyzed systems. On physiological time series, we found that paced breathing at slow breathing rates induces less complex and more coupled CR dynamics, while postural stress leads to unbalancing of CV interactions with prevalent baroreflex coupling and to less complex pressure dynamics with preserved CB interactions. These results are better highlighted by the permutation approach, thanks to its more parsimonious representation of the discretized dynamic patterns, which allows one to explore interactions with longer memory while limiting the curse of dimensionality

A New Framework for the Time- and Frequency-Domain Assessment of High-Order Interactions in Networks of Random Processes

While the standard network description of complex systems is based on quantifying the link between pairs of system units, higher-order interactions (HOIs) involving three or more units often play a major role in governing the collective network behavior. This work introduces a new approach to quantify pairwise and HOIs for multivariate rhythmic processes interacting across multiple time scales. We define the so-called O-information rate (OIR) as a new metric to assess HOIs for multivariate time series, and present a framework to decompose the OIR into measures quantifying Granger-causal and instantaneous influences, as well as to expand all measures in the frequency domain. The framework exploits the spectral representation of vector autoregressive and state space models to assess the synergistic and redundant interaction among groups of processes, both in specific bands of interest and in the time domain after whole-band integration. Validation of the framework on simulated networks illustrates how the spectral OIR can highlight redundant and synergistic HOIs emerging at specific frequencies, which cannot be detected using time-domain measures. The applications to physiological networks described by heart period, arterial pressure and respiration variability measured in healthy subjects during a protocol of paced breathing, and to brain networks described by electrocorticographic signals acquired in an animal experiment during anesthesia, document the capability of our approach to identify informational circuits relevant to well-defined cardiovascular oscillations and brain rhythms and related to specific physiological mechanisms involving autonomic control and altered consciousness. The proposed framework allows a hierarchically-organized evaluation of timeand frequency-domain interactions in dynamic networks mapped by multivariate time series, and its high flexibility and scalability make it suitable for the investigation of networks beyond pairwise interactions in neuroscience, physiology and many other fields

Statistical Approaches to Identify Pairwise and High-Order Brain Functional Connectivity Signatures on a Single-Subject Basis

Keeping up with the shift towards personalized neuroscience essentially requires the derivation of meaningful insights from individual brain signal recordings by analyzing the descriptive indexes of physio-pathological states through statistical methods that prioritize subject-specific differences under varying experimental conditions. Within this framework, the current study presents a methodology for assessing the value of the single-subject fingerprints of brain functional connectivity, assessed both by standard pairwise and novel high-order measures. Functional connectivity networks, which investigate the inter-relationships between pairs of brain regions, have long been a valuable tool for modeling the brain as a complex system. However, their usefulness is limited by their inability to detect high-order dependencies beyond pairwise correlations. In this study, by leveraging multivariate information theory, we confirm recent evidence suggesting that the brain contains a plethora of high-order, synergistic subsystems that would go unnoticed using a pairwise graph structure. The significance and variations across different conditions of functional pairwise and high-order interactions (HOIs) between groups of brain signals are statistically verified on an individual level through the utilization of surrogate and bootstrap data analyses. The approach is illustrated on the single-subject recordings of resting-state functional magnetic resonance imaging (rest-fMRI) signals acquired using a pediatric patient with hepatic encephalopathy associated with a portosystemic shunt and undergoing liver vascular shunt correction. Our results show that (i) the proposed single-subject analysis may have remarkable clinical relevance for subject-specific investigations and treatment planning, and (ii) the possibility of investigating brain connectivity and its post-treatment functional developments at a high-order level may be essential to fully capture the complexity and modalities of the recovery

En tiempos de COVID-19, de la presencialidad a la virtualidad : Cómo nos transformamos en una sociedad de la ubicuidad

Introducción: Históricamente ha sido lento el proceso de incorporación de las tecnologías a la educación. En lo que se refiere a las TIC, están en la educación actual. Sin embargo, un cambio cualitativo dentro del proceso de enseñanza- aprendizaje solo ocurre cuando se consigue integrar las TIC dentro de una visión innovadora. En la educación actual, la información avanzada ha favorecido el desarrollo de un nuevo ambiente de aprendizaje: la educación móvil. El desarrollo de las comunicaciones digitales móviles nos desplaza hacia la “sociedad de la ubicuidad”: comunicación para todos, en cualquier momento, en cualquier lugar. Solo teniendo la necesidad de móviles idóneos para responder a las exigencias del ambiente comunicativo que supone dicha sociedad Con el COVID–19 y la suspensión de la presencialidad es donde aparece la necesidad de sostener la continuidad pedagógica, logrando cumplir con todos los contenidos teóricos y analizando cumplimentar lo presencial con su práctica en clínica con la resolución de casos clínicos. Objetivos: cumplimentar con el uso de la virtualidad, los contenidos pedagógicos que se deben cumplir para completar con la formación educativa de las asistentes en odontología. Verificar habilidades y competencias que estiman necesarias y que practican en el uso de las herramientas virtuales.Facultad de Odontologí

Pluronic®/casein micelles for ophthalmic delivery of resveratrol: in vitro, ex vivo, and in vivo tests

Ocular health may strongly benefit from the supply of antioxidant agents that counteract free radicals and reactive oxygen species responsible for long-term eye diseases. Additionally, natural antioxidants like resveratrol can inhibit bacteria growth and restore natural microbiota. However, their use is hindered by limited solubility, fast degradation, and low ocular permeability. This work aimed to overcome these limitations by preparing single and mixed micelles of Pluronic® F127 and casein that serve as resveratrol nanocarriers. Single and mixed (0.1 % casein) micelles (0.0 to −17.0 mV; 2.4 to 32.7 nm) increased 50-fold resveratrol solubility, remained stable for one month at 4 °C, withstood fast dilution, underwent sol-to-gel transitions in the 23.9–27.1 °C range, and exhibited potent antioxidant properties. All formulations successfully passed the HET-CAM assay but showed Pluronic®-casein dose-dependent toxicity in the zebrafish embryo model. Resveratrol-loaded single and mixed micelles (10–15 mM Pluronic® F127) displayed antimicrobial activity against S. aureus and P. aeruginosa. The micelles favored resveratrol accumulation in cornea and sclera, but mixed micelles showed larger lag times and provided lower amount of resveratrol permeated through sclera. In vivo (rabbit) tests confirmed the safety of resveratrol-loaded single micelles and their capability to supply resveratrol to anterior and posterior eye segmentsThe work was supported by MCIN/AEI/10.13039/501100011033 [PID 2020-113881RB-I00 to A.C. and C.A.-L., and PID2020-115121GB-I00 to L.S. and A.B.-I.], Spain, Xunta de Galicia [ED431C 2020/17], and FEDER. M. Vivero-Lopez acknowledges Xunta de Galicia (Consellería de Cultura, Educación e Ordenación Universitaria) for a predoctoral research fellowship [ED481A-2019/120]S

Metodología de la enseñanza en instrumentación odontológica: el desafio virtual

Introducción: En tiempos de situaciones que se han precipitado, como es el que estamos viviendo con el COVID 19, nos sumergimos en tiempos de cambios, tiempos de duelo por implementaciones tecnológicas que no fueron y tiempos de ilusiones por lo que vendrá .La virtualidad se hizo presente. Como se observa, la no presencialidad, la utilización de tecnología y la puesta en marcha de un sistema pedagógico centrado en los estudiantes, son aspectos claves para la implementación de una educación virtual que responda a las necesidades de formación , para producir y generar conocimiento. Objetivos: El presente trabajo desea indagar en un grupo de docentes universitarios de la Tecnicatura de Asistencia Odontológica de la FOLP, sobre la incorporación del uso de plataformas virtuales a las prácticas de enseñanzas universitarias, indagando además sobre sus expectativas en el contexto atípico que nos toca vivir así como la interacción docente-estudiante en plataformas virtuales.Facultad de Odontologí

Opening The Door to Oral Health. Stage VI

Introducción: En este proyecto se desarrollaron actividades educativas individuales, grupales y familiares, así como también, a través de acciones preventivas orientadas a la disminución de los factores de riesgo, que contribuyen a la aparición de enfermedades bucales, revertir la problemática de lesiones cariosas en molares de niños de 3 a 11 años, considerando las edades de los destinatarios, como por ejemplo la relevancia del flúor como protección de la caries dental y la aplicación de selladores de fosas y fisuras, debido a la alta prevalencia. Objetivos: conocer índices epidemiológicos iniciales en pos de identificar problemáticas específicas para posible resolución, generar un cambio de actitud con respecto a los hábitos de higiene bucal, enseñar técnica de cepillado y el uso de complementos de higiene bucal, concientizar y capacitar a los padres para realizar acciones de autocuidado y la consulta periódica al odontólogo.Introduction In this project, individual, group and family educational activities were developed, as well as, through preventive actions aimed at reducing risk factors that contribute to the appearance of oral diseases, reversing the problem of carious lesions in molars of children from 3 to 11 years old, considering the ages of the recipients, such as the relevance of fluoride as protection against dental caries and the application of pit and fissure sealants, due to the high prevalence Objectives: to know initial epidemiological indices in order to identify specific problems for possible resolution, generate a change of attitude regarding oral hygiene habits, teach brushing technique and the use of oral hygiene supplements, raise awareness and train parents to perform self-care actions and regular consultation with the dentist.Facultad de Odontologí