Short-time Directed Transfer Function Research Articles

P27-T Common pattern of information transfer in the brain for different modalities during a reasoning task

Background Information processing in the brain involves the synchronization of brain structures realized by the transmission of rhythmic activity. The aim of our work was to find connectivity patterns between brain structures during the same mental activity performed during tasks with different stimuli modality. Material and methods The task: the paradigm of linear syllogism was performed with visual (12 subjects) and auditory stimuli (29 subjects). The EEG activity transmission was analyzed by means of the short-time Directed Transfer Function (sDTF), a frequency dependent estimator of directed coupling between time series based on the Granger causality principle. Results and conclusions The obtained patterns showed similar coupling for both modalities involving EEG propagation mainly between the frontal and posterior areas which communicated intermittently. Our results indicate that the fronto-parietal network operated mainly in the theta frequency range as well as in other frequency ranges, especially gamma. By means of the assortative mixing approach, the strengths of coupling between the regions of interests (ROIs) were determined. For both modalities, the results showed stronger coupling within the ROIs than between them in agreement with the theories considering information transfer efficiency and metabolic energy savings. The patterns differences were minor and concerned stronger propagation from the posterior electrodes towards the frontal ones during the visual task and from the temporal sites to the frontal ones during the auditory task, which can be explained as bottom-up communication from specific sensory sites. Our results support a modality-free process of information retrieval and integration in a reasoning task.

Coupling Between Brain Structures During Visual and Auditory Working Memory Tasks.

Transmission of EEG activity during a visual and auditory version of the working memory task based on the paradigm of linear syllogism was investigated. Our aim was to find possible similarities and differences in the synchronization patterns between brain structures during the same mental activity performed on different modality stimuli. The EEG activity transmission was evaluated by means of full frequency Directed Transfer Function (ffDTF) and short-time Directed Transfer Function (SDTF). SDTF provided information on dynamical propagation of EEG activity. The assortative mixing approach was applied to quantify coupling between regions of interest encompassing frontal, central and two posterior modules. The results showed similar schemes of coupling for both modalities with stronger coupling within the regions of interests than between them, which is concordant with the theories concerning efficient wiring and metabolic energy saving. The patterns of transmission showed main sources of activity in the anterior and posterior regions communicating intermittently in a broad frequency range. The differences between the patterns of transmission between the visual and auditory versions of working memory tasks were subtle and involved bigger propagation from the posterior electrodes towards the frontal ones during the visual task as well as from the temporal sites to the frontal ones during the auditory task.

Granger causal connectivity dissociates navigation networks that subserve allocentric and egocentric path integration

Studies on spatial navigation demonstrate a significant role of the retrosplenial complex (RSC) in the transformation of egocentric and allocentric information into complementary spatial reference frames (SRFs). The tight anatomical connections of the RSC with a wide range of other cortical regions processing spatial information support its vital role within the human navigation network. To better understand how different areas of the navigational network interact, we investigated the dynamic causal interactions of brain regions involved in solving a virtual navigation task. EEG signals were decomposed by independent component analysis (ICA) and subsequently examined for information flow between clusters of independent components (ICs) using direct short-time directed transfer function (sdDTF). The results revealed information flow between the anterior cingulate cortex and the left prefrontal cortex in the theta (4–7 Hz) frequency band and between the prefrontal, motor, parietal, and occipital cortices as well as the RSC in the alpha (8–13 Hz) frequency band. When participants prefered to use distinct reference frames (egocentric vs. allocentric) during navigation was considered, a dominant occipito-parieto–RSC network was identified in allocentric navigators. These results are in line with the assumption that the RSC, parietal, and occipital cortices are involved in transforming egocentric visual-spatial information into an allocentric reference frame. Moreover, the RSC demonstrated the strongest causal flow during changes in orientation, suggesting that this structure directly provides information on heading changes in humans.

Directed Transfer Function is not influenced by volume conduction-inexpedient pre-processing should be avoided.

Directed Transfer Function is not influenced by volume conduction-inexpedient pre-processing should be avoided.

Application of directed transfer function and network formalism for the assessment of functional connectivity in working memory task

The dynamic pattern of functional connectivity during a working memory task was investigated by means of the short-time directed transfer function. A clear-cut picture of transmissions was observed with the main centres of propagation located in the frontal and parietal regions, in agreement with imaging studies and neurophysiological hypotheses concerning the mechanisms of working memory. The study of the time evolution revealed that most of the time short-range interactions prevailed, whereas the communication between the main centres of activity occurred more sparsely and changed dynamically in time. The patterns of connectivity were quantified by means of a network formalism based on assortative mixing--an approach novel in the field of brain networks study. By means of application of the above method, we have demonstrated the existence of a modular structure of brain networks. The strength of interaction inside the modules was higher than between modules. The obtained results are compatible with theories concerning metabolic energy saving and efficient wiring in the brain, which showed that preferred organization includes modular structure with dense connectivity inside the modules and more sparse connections between the modules. The presented detailed temporal and spatial patterns of propagation are in line with the neurophysiological hypotheses concerning the role of gamma and theta activity in information processing during a working memory task.

Review of the methods of determination of directed connectivity from multichannel data.

The methods applied for estimation of functional connectivity from multichannel data are described with special emphasis on the estimators of directedness such as directed transfer function (DTF) and partial directed coherence. These estimators based on multivariate autoregressive model are free of pitfalls connected with application of bivariate measures. The examples of applications illustrating the performance of the methods are given. Time-varying estimators of directedness: short-time DTF and adaptive methods are presented.

Transmission of Brain Activity During Cognitive Task

The transmission of brain activity during constant attention test was estimated by means of the short-time directed transfer function (SDTF). SDTF is an estimator based on a multivariate autoregressive model. It determines the propagation as a function of time and frequency. For nine healthy subjects the transmission of EEG activity was determined for target and non-target conditions corresponding to pressing of a switch in case of appearance of two identical images or withholding the reaction in case of different images. The involvement of prefrontal and frontal cortex manifested by the propagation from these structures was observed, especially in the early stages of the task. For the target condition there was a burst of propagation from C3 after pressing the switch, which can be interpreted as beta rebound upon completion of motor action. In case of non-target condition the propagation from F8 or Fz to C3 was observed, which can be connected with the active inhibition of motor cortex by right inferior frontal cortex or presupplementary motor area.

Methods for determination of functional connectivity in brain

Event Abstract Back to Event Methods for determination of functional connectivity in brain Katarzyna Blinowska1* 1 University of Warsaw, Poland The methods applied for estimation of functional connectivity are presented with special emphasis on the estimators of directedness such as Directed Transfer Function and Partial directed Coherence. Time-varying estimator of directedness Short-time Directed Transfer Function is described. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Oral Presentation Topic: Signal proccessing Citation: Blinowska K (2010). Methods for determination of functional connectivity in brain. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00018 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 19 Mar 2010; Published Online: 19 Mar 2010. * Correspondence: Katarzyna Blinowska, University of Warsaw, Granz, Poland, kjbli@fuw.edu.pl Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Katarzyna Blinowska Google Katarzyna Blinowska Google Scholar Katarzyna Blinowska PubMed Katarzyna Blinowska Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Transmission of information during Continuous Attention Test.

The Short-Time Directed Transfer Function (SDTF) is an estimator based on a multivariate autoregressive model which has proved to be successful in ERP experiments, e.g. those connected with motor action and its imagination. The aim of this study is the evaluation of the performance of SDTF in the cognitive experiment. We have applied SDTF for the estimation of the pattern of EEG signal transmissions during a Continuous Attention Test (CAT). Time-frequency patterns of propagation were estimated for two experimental conditions. Statistical procedures based on thin-plate spline model were used for estimation of significant changes in respect to the reference epoch. The repeatability of the results for a subject and across the subjects were investigated. The effect of prolonged transmission in the gamma band from the prefrontal electrodes found in all subjects was explained by the active inhibition in the case when a subject had to sustain from performing the action.

Dynamics of event‐related causality in brain electrical activity

A new method (Event-Related Causality, ERC) is proposed for the investigation of functional interactions between brain regions during cognitive processing. ERC estimates the direction, intensity, spectral content, and temporal course of brain activity propagation within a cortical network. ERC is based upon the short-time directed transfer function (SDTF), which is measured in short EEG epochs during multiple trials of a cognitive task, as well as the direct directed transfer function (dDTF), which distinguishes direct interactions between brain regions from indirect interactions via brain regions. ERC uses new statistical methods for comparing estimates of causal interactions during prestimulus "baseline" epochs and during poststimulus "activated" epochs in order to estimate event-related increases and decreases in the functional interactions between cortical network components during cognitive tasks. The utility of the ERC approach is demonstrated through its application to human electrocorticographic recordings (ECoG) of a simple language task. ERC analyses of these ECoG recordings reveal frequency-dependent interactions, particularly in high gamma (>60 Hz) frequencies, between brain regions known to participate in the recorded language task, and the temporal evolution of these interactions is consistent with the putative processing stages of this task. The method may be a useful tool for investigating the dynamics of causal interactions between various brain regions during cognitive task performance.

Propagation of EEG activity during finger movement and its imagination

We investigated the pattern of EEG activity propagation in the beta and gamma band during a finger movement experiment and imagination of that task. The data were analyzed by means of a short-time directed transfer function (SDTF) based on a multivariate autoregressive model. The signals from the right (or left) hemisphere were processed simultaneously (not pairwise), which is crucial for obtaining a correct picture of EEG activity transmissions. The pattern of propagation in the beta band involved for both tasks a decrease of the propagation from the motor areas during the execution of the movement ? less pronounced in the case of imagination. The performance of the motion was mainly connected with a short outburst of gamma activity from the hand sensorimotor areas. In case of imagination the gamma outflow lasted longer and concerned larger brain areas.

Analysis of multichannel biomedical data

Nowadays, there is a common practice in biomedical research to perform multiple time series recordings. In the first part of this paper, basic information about analysis of such multichannel biomedical data is given. A short overview of important differences between single-channel, two-channel and multichannel data sets is presented and various coherence functions are reported. Causal relations between channels are investigated by means of the Directed Transfer Function (DTF) and its dynamic version, the Short-Time Directed Transfer Function (SDTF). The introduced formalism was used to analyze 12-channel human electrocorticogram (ECoG) records. Preliminary results of a study of causal dependence in beta and gamma frequency bands in two patients performing a motor task are reported. Specific characteristics in activity propagation consistent for both subjects for different rhythms were found.

Propagation of EEG Activity in the Beta and Gamma Band during Movement Imagery in Humans

The objective of the paper was the determination of electrical brain activity propagation in sensorimotor areas during hand movement imagery. Right-hand and left-hand movement imagination was studied in three subjects. The 10-channel Multivariate Autoregressive Model (MVAR) was fitted to EEG signals recorded from subsets of electrodes overlying central and related brain areas. By means of the Short-time Directed Transfer Function (SDTF) the propagation of brain activity as a function of frequency and time was found. During imagery the relation between propagations in gamma and beta bands changed significantly for electrodes overlying sensorimotor areas, namely the increase in gamma was accompanied by the decrease in the beta band. The hypothesis was put forward that these kinds of changes in flow of electrical brain activity are connected with the specific information processing.

Phase and amplitude analysis in time–frequency space—application to voluntary finger movement

Two methods operating in time–frequency space were applied to analysis of EEG activity accompanying voluntary finger movements. The first one, based on matching pursuit approach provided high-resolution distributions of power in time–frequency space. The phenomena of event related desynchronization (ERD) and synchronization (ERS) were investigated without the need of band-pass filtering. Time evolution of μ- and β-components was observed in a detailed way. The second method was based on a multichannel autoregressive model (MVAR) adapted for investigation of short-time changes in EEG signal. The direction and spectral content of the EEG activity propagation was estimated by means of short-time directed transfer function (SDTF). The evidence of ‘cross-talk’ between different areas of motor and sensory cortex was found. The earlier known phenomena, connected with voluntary movements, were confirmed and a new evidence concerning focal ERD/surround ERS and β activity post-movement synchronization was found.

Causal influences in primate cerebral cortex during visual pattern discrimination.

Anatomical studies of the visual cortex demonstrate the existence of feedforward, feedback and lateral pathways among multiple cortical areas. Yet relatively little evidence has previously been available to show the causal influences of these areas on one another during visual information processing. We simultaneously recorded event-related local field potentials (LFPs) from surface-to-depth bipolar electrodes at six sites in the ventral region of the right hemisphere visual cortex in a highly trained macaque monkey during performance of a visual pattern discrimination task. Applying a new statistical measure, the short-time directed transfer function (STDTF), to the LFP data set, we charted the changing strength and direction of causal influence between these cortical sites on a fraction-of-a-second time scale. We present results showing, for the first time, the dynamics of distinct feedforward, feedback and lateral influences in the ventral portion of the primate visual cortex during visual pattern processing.