Functional near-infrared spectroscopy for monitoring macaque cerebral motor activity during voluntary movements without head fixation

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The durations of food retrieval events in 75 trials of each left- and right-hand use in each experimental session were sampled. For normalizing the sample distributions, the Box–Cox transformation with λ = −1 was applied for each session data. The homoscedasticity among the transformed distributions was examined with Bartlett’s test. Differences among the sample averages of different sessions and used hands were compared using analysis of variance (ANOVA) with correction for multiple comparisons using the Tukey–Kramer method.

The fNIRS data in each of the 150 trials (75 right hand, 75 left hand) was time-locked (t = 0) to the onset of food retrieval movement for that trial. Then the values of ΔHbO and ΔHbR for each time point (i.e., a 130 ms period, starting from t = 0 for each trial) were averaged and plotted in Fig. 4 (and in Fig. 5 for additional tasks). For each time point, a paired t-test between the left-hand trials and right-hand trials was also conducted. Figure 6 plots the t-score values for the contrast of left versus right hand movement, for both ΔHbO and ΔHbR, at each time point in each of the eight sessions. When significant amplitude (p < 0.05) in the t-value curves was detected, the maximum amplitude in the ΔHbO and ΔHbR curves and the time elapsed from onset to maximum amplitude was calculated. These calculations at each channel were performed for each experimental session. Maximum amplitude and elapsed time in each session were averaged between channels for each brain hemisphere separately and the Pearson’s product-moment correlation coefficient of them against the time required for food retrieval were calculated.

Figure 4
Figure 4
Representative hemodynamic response during a food retrieval experimental session. (a) Left-hand use and (b) right-hand use. Each frame depicts the block averages and the standard deviations of each channel among for ΔHbO and ΔHbR drawn with red and blue lines and bands, respectively.
Figure 5
Figure 5
Hemodynamic responses evoked by different restrained conditions. (A) Left hand food retrieval with the right forelimb constrained and (B) direct feeding to mouth with both hands restrained. Each frame depicts the block averages and the standard deviations of each channel among for ΔHbO and ΔHbR drawn with red and blue lines and bands, respectively.
Figure 6
Figure 6
(a) Time course curves of paired t-values of hemodynamic response. The t-values for the paired t-test were calculated from the difference in hemodynamics during trials of left-hand and right-hand use. The t-values of ΔHbO and ΔHbR for each of the eight sessions were drawn with red and blue lines, respectively. The dotted lines in each frame indicate levels of p = 0.05. (b) Color-mapping of t-values onto the subject’s anatomical MRI. The t-values for ΔHbO of the first session using a food well of 20 mm 5 s after task onset are depicted. Arrows indicate the positions of “hand knob” in each hemisphere.

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