Vector-Based Approach for the Detection of Initial Dips Using Functional Near-Infrared Spectroscopy

Abstract

Functional near-infrared spectroscopy (fNIRS) is a non-invasive method for the detection of local brain activity using changes in the local levels of oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb). Simultaneous measurement of the levels of oxyHb and deoxyHb is an advantage of fNIRS over other modalities. This review provides a historical description of the physiological problems involved in the accurate identification of local brain activity using fNIRS. The need for improved spatial and temporal identification of local brain activity is described in terms of the physiological challenges of task selection and placement of probes. In addition, this review discusses challenges with data analysis based on a single index, advantages of the simultaneous analysis of multiple indicators, and recently established composite indicators. The vector-based approach provides quantitative imaging of the phase and intensity contrast for oxygen exchange responses in a time series and may detect initial dips related to neuronal activity in the skull. The vector plane model consists of orthogonal vectors of oxyHb and deoxyHb. Initial dips are hemodynamic reactions of oxyHb and deoxyHb induced by increased oxygen consumption in the early tasks of approximately 2-3 seconds. The new analytical concept of fNIRS, able to effectively detect initial dips, may extend further the clinical and social applications of fNIRS.

Hemodynamic Response Detection Using Integrated EEG-fNIRS-VPA for BCI

“…Magnitude and angle, calculated using HbO and HbR, are used to construct a two-dimensional vector plane [33]. This plane is divided into eight phases for the classification of hemodynamic response [34]. A threshold circle is plotted on the vector plane to detect brain activity [35].…”

“…If the trajectory of HbO and HbR crosses this threshold circle, this indicates activity. Magnitude values less than this threshold circle are considered as resting-state [34,35,38]. Initial dip and hemodynamic response can be detected in these eight phases.…”

Vector-based analysis of cortical activity associated with dumbbell exercise using functional near-infrared spectroscopy

“…OxyHb increased and deoxyHb fell slightly in the sensory-motor cortex and the pre-SMA (Hatakenaka et al, 2007 ). Several reports have shown that oxyHb analysis alone cannot accurately detect the localization of neuroactivation (Cyranoski, 2011 ; Takahashi et al, 2011 ) and that functional images of increasing oxyHb may differ from the actual distribution of oxygen consumption (Kato, 2018 , 2021 ).…”

“…However, the oxygen consumption and supply triggered by neuroactivation cannot be evaluated simultaneously based on deoxyHb alone. In terms of technological advances, earlier NIRS was used as a cerebral oxygen monitor that could be measured over the scalp, and it was not until July 1991 that it was first successfully demonstrated that fNIRS could detect regional brain function (Kato, 2018 ). In addition, there was a lack of theory to quantitatively integrate neural activation from multiple sites (channels) and indices (Kato et al, 1993 ; Ferrari and Quaresima, 2012 ).…”

“…A technique has been proposed for detecting and imaging the spatial distribution of neuroactivation by differentiating the phase distributions of oxygen consumption and oxygen supply (Kato et al, 2003 ; Kato, 2018 ). Temporal FORCE effects were reported to be detected 2–3 s after the onset of the stimulus task.…”