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Effects of different smoothing on global and regional resting functional connectivity

  • Functional Neuroradiology
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Abstract

Purpose

Spatial smoothing is an essential pre-processing step in the process of analysing functional magnetic resonance imaging (fMRI) data, both during an experimental task or during resting-state fMRI (rsfMRI). The main benefit of this spatial smoothing step is to artificially increase the signal-to-noise ratio of the fMRI signal. Previous fMRI studies have investigated the impact of spatial smoothing on task fMRI data, while rsfMRI studies usually apply the same analytical process used for the task data. However, this study investigates changes in different rsfMRI analyses, such as ROI-to-ROI, seed-to-voxels and ICA analyses.

Methods

Nineteen healthy volunteers were scanned using rsfMRI with three applied smoothing kernels: 0 mm, 4 mm and 8 mm. Appropriate statistical comparisons were made.

Results

The findings showed that spatial smoothing has a greater effect on rsfMRI data when analysed using seed-to-voxel-based analysis. The effect was less pronounced when analysing data using ROI-ROI or ICA analyses. The results demonstrated that even when analysing the data without the application of spatial smoothing, the results were significant compared with data analysed using a typical smoothing kernel. However, data analysed with lower-smoothing kernels produced greater negative correlations, particularly with the ICA analysis.

Conclusion

The results suggest that a medium smoothing kernel (around 4 mm) may be preferable, as it is comparable with the 8 mm kernel in all of the analyses performed. It is also recommended that the researchers consider analysing the data using two different smoothing kernels, as this will help to confirm the significance of the results and avoid overestimating the findings.

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Funding

This project was funded by the deanship of Scientific Research (DSR) at King Abdulaizz University (KAU), Jeddah. The author, therefore, acknowledges with thanks DSR for technical support.

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Authors and Affiliations

  1. Department of Radiologic Sciences, College of Applied Medical Science, King Abdulaziz University (KAU), Jeddah, Saudi Arabia

    Adnan A. S. Alahmadi

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  1. Adnan A. S. Alahmadi
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Correspondence to Adnan A. S. Alahmadi.

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The author declares that there is no conflict of interest.

Ethical approval

The data samples were taken from the Leiden_2200 data sample (open access) (http://fcon_1000.projects.nitrc.org). All procedures performed in the studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from all individual participants included in the study. The included participant data were taken from the Leiden_2200 dataset which is part of the 1000 functional connectomes project.

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Cite this article

Alahmadi, A.A.S. Effects of different smoothing on global and regional resting functional connectivity. Neuroradiology 63, 99–109 (2021). https://doi.org/10.1007/s00234-020-02523-8

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  • DOI: https://doi.org/10.1007/s00234-020-02523-8

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