Cluster structure and localization of brain functional networks based on the ERP signals of auditory task

报告人：蔡世民合作者：禚钊，乔赫元，傅忠谦，周佩玲

电子科学与技术系

Outline

• Introduction • Data Acquisition• Phase Synchronization• Results

Introduction

• What is brain functional networks? A brain functional network can be derived from the physiological signals such as EEG,MEG, ECoG, and fMRI. Nodes: ROIs (fMRI) or channels (EEG,MEG,ECoG). Edges : correlation (interaction) between ROIs or channels.

Introduction (cont.)

• Construction of large-scale brain functional networks--Pearson correlation coefficient--Correlation coefficient based on Wavelet transform--Mutual information --Nonlinear interdependence --Phase synchronization based on Hilbert transform

Introduction (cont.)

Network Extracted

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Correlation Matrix1

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Binary Matrix1

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Introduction (cont.)

• Brain functional networks posses some common structures of complex networks

--small-world property (D. S. Bassett, Neuroscientist 12, 512, 2006)

--scale-free property (V. M. Eguiluz, et al. PRL 94, 018102, 2005)

--Hierarchical organization (C. S. Zhou, et al. PRL 97, 238103, 2006)

Data Acquisition • Five persons were asked to distinguish between synonymous and non-

synonymous word pairs (the second word presented 1 second after the first) they heard.

• Data epochs were extracted from 2 sec before the second word onset to 2 sec after the second word onset.

• Sampling rate (Hz) 200.

Data Acquisition (cont.)

• 61-channel ERP signal.

Letters refer to the main areas of the cortex: F: the frontal (额叶 ), T: left and right temporal (颞叶 ), P: the parietal (顶叶 ),O: the occipital (枕叶 ),C : central, FP: frontopolar(额极 ), AF: anterior frontal(前额叶 ).

Data Acquisition (cont.)

• The testee was cued to move a particular figure by displaying the corresponding word,

such as “thumb”;• Each cue lasted two seconds following an another two seconds resting period;• Band pass filtered between 0.15 and 200 Hz,

and sampled at 1000 Hz;• The experiment lasted 400 seconds for echa

testee.

Data Acquisition (cont.)

Sketch of ECoG recording

Phase Synchronization

• Phase of real value time series

• bivariate phase synchronization index

If two time series are complete phase synchronized, this value will be the maximum.

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Generating Networks• Divide data into four parts:1st ,2nd ,3rd and 4th second.

resting state: 1st and 4th seconds; auditory task state: 2nd and 3rd seconds

• Fixed mean degree for four partsmean degree: 4-30,increasedby 2.The thresholds as a function of mean degree k .⟨ ⟩

Generating Networks (cont.)

• Divide data into two parts: -- task state: 1st 2 seconds-- resting: 2nd 2 seconds• Fixed mean degree for two parts --mean degree: 4-30,increased

by 2. ECoG

Results• Networks show different property during rest

and task state for EEG

Results (cont.)• Networks show different property during

rest and task state for ECoG

Results (cont.)

Results (cont.)

• Networks show small-world property

EEGECoG

6.Conclusion and outlook• The diversity of topology between the resting and task states suggests the

variance of correlations among the functional modules. • The larger cluster coefficients during task mean that the correlations of

cortex regions are more localized in the large-scale brain functional networks

• The connectivity of networks under task state presents a better performance than that under resting state via the estimation of giant components’ sizes.

• Moreover, the mean path lengths of brain functional networks confirm the small world property.

• Future work will focus on the location of community during the cognitive process and the relationship between the large-scale functional networks and micro-scale neural dynamics via diffusion

tensor imaging