Non-neuronal evoked and spontaneous hemodynamic changes in the anterior temporal region of the human head may lead to misinterpretations of functional near-infrared spectroscopy signals

Fig. 1. Distribution of the source and detector locations for the task-related (a, created based on Refs. 22 and 23) and resting-state related data (b). Channels in green presented negative [O2Hb] to [HHb] correlation, the channels in red yielded a positive correlation, and the channel in yellow presented median correlation close to zero (within the range limited by −0.1 and 0.1). The correlation results shown in this figure correspond to group-level results, as described in Sec. 3.

Fig. 2. Task-evoked results for four illustrative channels with color correspondence to the spatial distribution in Fig. 1(a). Boxplots with correlation results over all subjects are shown on the top. Block average results (over runs) of a representative subject (#08) are depicted on bottom. [O2Hb] time series are plotted as red and [HHb] as blue signals. The shaded area represents the standard deviation.

Fig. 3. Scatter plots of different metrics of the BVPA (y-axis) with respect to the [O2Hb] to [HHb] correlation (x-axis) for task-evoked data. From left to right and then top to bottom, the BVPA metrics are: (a) peak-to-peak, (b) mean, (c) variance, and (d) median absolute deviation (mad). For each metric, a polynomial fit has been applied to the data (red), whereas the orange curves represent the 95% confidence interval. A linear fit was empirically found to better fit the mean, whereas the quadratic fit for all the other metrics. Each graph presents the correlation (ρ) between the variables as well as the adjusted coefficient of determination (R2). Colored points (green, yellow, and red) relate to color-coded channels in Fig. 1(a). Channels highlighted in Fig. 2 are marked with a white number (28, 29, 40, and 51).

Fig. 4. Boxplots illustrating the [O2Hb] to [HHb] resting-state correlation results over all subjects for each region of interest according to the underlying anatomical regions. The red box highlights the anterior temporal region (channels 14, 21, 28, 29, and 30).

Fig. 5. (a) The median channel-wise correlation over all subjects (resting-state data) is depicted with scaled colors for different chromophores. Orange arrows have been added on top of each image to indicate the channels related to the anterior temporal region. (b) The scatter plots of the median channel-wise correlation for each chromophore in respect to the [O2Hb] to [HHb] correlation. Red curves indicate the quadratic fit and the orange lines the 95% confidence interval. On the left superior corner, corresponding ρ and R2 values for each plot are shown.

Fig. 6. Modified from Ref. 42: extracranial vessels (a) and head muscles (b) of a right-hand specimen. Subfigure (c) highlights the temporalis muscle.