Send to

Choose Destination
Neurophotonics. 2019 Jan;6(1):015001. doi: 10.1117/1.NPh.6.1.015001. Epub 2019 Jan 9.

Denoising of neuronal signal from mixed systemic low-frequency oscillation using peripheral measurement as noise regressor in near-infrared imaging.

Author information

Hitachi, Ltd., Center for Exploratory Research, Research & Development Group, Akanuma, Hatoyama, Saitama, Japan.
Universiti Teknologi PETRONAS, Electrical and Electronic Engineering Department, Bandar Seri Iskandar, Tronoh Perak, Malaysia.
McLean Hospital, Brain Imaging Center, Belmont, Massachusetts, United States.
Yanshan University, School of Information Science and Engineering, Qinhuangdao, China.
Harvard Medical School, Department of Psychiatry, Boston, Massachusetts, United States.
Purdue University, Weldon School of Biomedical Engineering, West Lafayette, Indiana, United States.


Functional near-infrared spectroscopy (fNIRS) is a noninvasive functional imaging technique measuring hemodynamic changes including oxygenated ( O 2 Hb ) and deoxygenated (HHb) hemoglobin. Low frequency (LF; 0.01 to 0.15 Hz) band is commonly analyzed in fNIRS to represent neuronal activation. However, systemic physiological artifacts (i.e., nonneuronal) likely occur also in overlapping frequency bands. We measured peripheral photoplethysmogram (PPG) signal concurrently with fNIRS (at prefrontal region) to extract the low-frequency oscillations (LFOs) as systemic noise regressors. We investigated three main points in this study: (1) the relationship between prefrontal fNIRS and peripheral PPG signals; (2) the denoising potential using these peripheral LFOs, and (3) the innovative ways to avoid the false-positive result in fNIRS studies. We employed spatial working memory (WM) and control tasks (e.g., resting state) to illustrate these points. Our results showed: (1) correlation between signals from prefrontal fNIRS and peripheral PPG is region-dependent. The high correlation with peripheral ear signal (i.e., O 2 Hb ) occurred mainly in frontopolar regions in both spatial WM and control tasks. This may indicate the finding of task-dependent effect even in peripheral signals. We also found that the PPG recording at the ear has a high correlation with prefrontal fNIRS signal than the finger signals. (2) The systemic noise was reduced by 25% to 34% on average across regions, with a maximum of 39% to 58% in the highly correlated frontopolar region, by using these peripheral LFOs as noise regressors. (3) By performing the control tasks, we confirmed that the statistically significant activation was observed in the spatial WM task, not in the controls. This suggested that systemic (and any other) noises unlikely violated the major statistical inference. (4) Lastly, by denoising using the task-related signals, the significant activation of region-of-interest was still observed suggesting the manifest task-evoked response in the spatial WM task.


brain; denoising; low-frequency oscillation; near-infrared spectroscopy; peripheral; systemic noise; working memory

[Available on 2020-01-09]

Supplemental Content

Loading ...
Support Center