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. 2017 Oct 30;8(11):5326-5341.
doi: 10.1364/BOE.8.005326. eCollection 2017 Nov 1.

Dynamics of the human brain network revealed by time-frequency effective connectivity in fNIRS

Grégoire Vergotte  1 , Kjerstin Torre  1 , Venkata Chaitanya Chirumamilla  2 , Abdul Rauf Anwar  3 , Sergiu Groppa  2 , Stéphane Perrey  1 , Muthuraman Muthuraman  2
Affiliations

Dynamics of the human brain network revealed by time-frequency effective connectivity in fNIRS

Grégoire Vergotte et al. Biomed Opt Express. .

Abstract

Functional near infrared spectroscopy (fNIRS) is a promising neuroimaging method for investigating networks of cortical regions over time. We propose a directed effective connectivity method (TPDC) allowing the capture of both time and frequency evolution of the brain's networks using fNIRS data acquired from healthy subjects performing a continuous finger-tapping task. Using this method we show the directed connectivity patterns among cortical motor regions involved in the task and their significant variations in the strength of information flow exchanges. Intra and inter-hemispheric connections during the motor task with their temporal evolution are also provided. Characterisation of the fluctuations in brain connectivity opens up a new way to assess the organisation of the brain to adapt to changing task constraints, or under pathological conditions.

Keywords: (100.4992) Pattern, nonlinear correlators; (110.3080) Infrared imaging.

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Conflict of interest statement

The authors declare no conflicts of interest, financial or otherwise.

Figures

Fig. 1
Fig. 1
On the left, fNIRS probes location using BrainNet Viewer [56] with transmitters (in red), receivers (in blue) and channels (Ch, in yellow). On the right, mean MNI coordinates and Brodmann area (BA) correspondence for each channel, to check to what extent fNIRS signals reflect the effect of several cerebral areas (represented in %) due to the spatial resolution of the system.
Fig. 2
Fig. 2
Flow chart of the various steps used for the TPDC analysis. The black arrows and rectangles (left side) present the overall process using real fNIRS data. The dotted gray arrows and rectangles (right side) display the bootstrapping process undertaken.
Fig. 3
Fig. 3
Example of time-frequency plots generated by TPDC analysis during 60 seconds of the finger-tapping task for 2 connections (From M1L to PMCL and PMCR to PMCL. a) Time frequency plot for the whole frequency band (5 Hertz). X-axis represents time in seconds. Y-axis the frequency in Hertz. Color bars represent the normalised (0 to 1) coherence of the connectivity extracted from TPDC results (blue close to zero connection and yellow close to 1 representing strong connection). b) Time frequency plot for the frequency band of interest [0.009 to 0.08 Hz]. c) Mean of the frequency band of interest. Y-axis represents strength of connection. This example shows higher connectivity strength from M1L to PMCL compared to PMCR to PMCL.
Fig. 4
Fig. 4
Whole surviving connections after bootstrapping analysis (n = 14). In blue, bi-directional connections (inter-hemispheric) and in red uni-directional connections located only in the contralateral hemisphere.
Fig. 5
Fig. 5
Average of the TPDC results with Box-plot, individual values and brain representation. Box-plot reflects median, quartile and dots of individuals values for each subject. X-axis represents connections. Y-axis is the mean TPDC value. Stars indicate Anova statistical significance at p = 0.05. On the right, representation of statistical significance on brain surfaces (differences are represented between red and blue connections).
Fig. 6
Fig. 6
Standard deviation and entropy of the TPDC results with Box-plot, individual values and brain representation. Box-plots in a) and b) reflect median, quartile and dots of individuals values for each subject. X-axis represents connections. Stars indicate Anova statistical significance at p = 0.05. a) STD TPDC. b) Entropy TPDC. c) Representation for both STD and Entropy of statistical significance on brain surfaces (differences are represented between red and blue connections).
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