Different mechanosensory stimulations of the lower back elicit specific changes in hemodynamics and oxygenation in cortical sensorimotor areas—A fNIRS study

Figures

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  Figure 1. Experimental setup. (A) Subject lying in prone position on a massage bench, while the examinant is applying a posterior‐to‐anterior pressure on the force sensor attached on third lumbar spinous process (L3). (B) Pressure sensor from top view, attached on the L3. (C) The force sensor from the bottom (this side is placed on the skin), (D) The inside of the force sensor. (E) The optodes, left with 1) the enclosure of the optic fibers and 2) the tip of the light emission diode (LED) source and right of the detector. (F) Probe array on the subjects head, (G) Fixation of a source and detector distance by using so‐called distance holders

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  Figure 2. Probe array (A) and its sensitivity profile [per mm] (calculated using AtlasViewer as implemented in HOMER2) from different views (A–D). The probe array displays the sources (red rhombi), the detectors (yellow circles), and the channels (black lines, numbered; the two short‐distance channels are marked with pink lines and numbers). The sensitivity values are displayed in log10 units. The profile was calculated for 10 million photons

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  Figure 3. Grand average of evoked hemodynamic changes in all subjects (Analysis_All) due to the brushing stimulus on the SMA (A) and S1 (B). Changes in [O2Hb] (red) and [HHb] (blue) are depicted as changes in the median concentration. The two vertical lines within the graph represent the stimulus on‐ and offset (duration = 5 s). Error bars represent the standard error of the median

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  Figure 4. Grand average of evoked hemodynamic changes in all subjects (Analysis_All) due to the nonpainful PA‐pressure stimulus (PA30) on the SMA (A) and S1 (B). Changes in [O2Hb] (red) and [HHb] (blue) are depicted as changes in the median concentration. The two vertical lines within the graph represent the stimulus on‐ and offset (duration = 5 s). Error bars represent the standard error of the median. Significant changes (q < 0.05; corrected for multiple comparison via [FDR]) are marked with a “*”

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  Figure 5. Grand average of evoked hemodynamic changes in all subjects (Analysis_All) due to the painful PA‐pressure stimulus (PAPain) on the SMA (A) and S1 (B). Changes in [O2Hb] (red) and [HHb] (blue) are depicted as changes in the median concentration. The two vertical lines within the graph represent the stimulus on‐ and offset (duration = 5 s). Error bars represent the standard error of the median. Significant changes (q < 0.05; corrected for multiple comparison [via FDR]) are marked with a “*”

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  Figure 6. Visualization of statistically significant channels in different comparisons for [O2Hb]. (A) Brushing stimulus versus baseline, (B) Nonpainful posterior‐to‐anterior (PA) stimulus (PA30) versus baseline, (C) Painful PA‐pressure stimulus (PAPain) versus baseline, (D) PAPain versus the brushing stimulus, and finally, (E) PA30 versus the brushing stimulus. Therefore, red lines display statistically significant channels in comparisons versus baseline, whereas green lines display significant channels in comparisons of the conditions against each other (q < 0.05, corrected for multiple comparisons using false discovery rate [FDR])

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  Figure 7. Grand average of evoked hemodynamic changes in all three conditions in the two short‐distance channels (channels 2 and 10) before the application of the short separation regression. (A–C): Short‐distance channel in the supplementary motor area (SMA) in the brushing condition (A), in the nonpainful condition (B), and in the painful condition (C). (D–F): Short‐distance channel in the primary somatosensory cortex (S1) in the brushing condition (D), in the nonpainful condition (E), and in the painful condition (F)

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  Figure 8. The average maximal heart rate (HR max) of all subjects during the stimuli and during the postinterstimulus intervals (post‐ISI). A statistical comparison was calculated by using Wilcoxon paired tests, yielding significant differences between the HR max of the stimulus and the HR max of the post‐ISI. Significance is indicated by stars (**: p < .002; ***: p < .001; corrected for multiple comparison [via FDR])