Breathing‐driven modulation of reticulospinal tract activity

Figures

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  FIGURE 1. Recording of the StartReact experiment. (a) The participant was equipped with a mask containing a sensor to monitor respiratory signals and was instructed to perform an elbow flexion and a power grip as soon as the LED light was activated. The light could be delivered alone (blue condition; VRT) or accompanied by a quiet sound (green condition; VART) or by a loud, startling sound (red condition; VSRT). (b) All conditions were presented in a randomized order while recording the respiratory signal, in addition to EMG activity from the first dorsal interosseous (1DI), flexor digitorum superficialis (FDS) and biceps muscles. (c) The respiratory signal (black trace) was segmented into six distinct phases, with a decrease in temperature during inspiration and an increase during expiration. Both the inspiration and expiration cycles were divided into three equidistant phases: start of inspiration (red, I1), middle of inspiration (orange, I2), end of inspiration (yellow, I3), start of expiration (green, E1), middle of expiration (blue, E2) and end of expiration (magenta, E3). Stimulations were categorized according to the respiratory phase in which they occurred. In this example, a VART…

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  FIGURE 2. Rectified EMG traces, reaction times and StartReact effects for VRT, VART and VSRT conditions across muscles. (a) Rectified EMG traces for the first dorsal interosseous (1DI, left), flexor digitorum superficialis (FDS, middle) and biceps (Bic, right) muscles during the VRT (blue), VART (green) and VSRT (red) conditions in a representative participant. Reaction times shortened during the VSRT condition compared with the VART and VRT conditions across all muscles. The black arrows indicate the time of the cue, and the blue, green and red arrows show the mean reaction times for the VRT, VART and VSRT conditions, respectively. (b) Bar charts showing reaction times for the VRT, VART and VSRT conditions across the 1DI, FDS and biceps muscles. Data are presented as the mean + SD. Individual data points from all participants (n = 13) are overlaid. Asterisks indicate statistically significant differences based on the Mann–Whitney U‐test (*P < 0.05, **P < 0.01 and ***P < 0.001). (c) StartReact effect (VART–VSRT difference) across muscles. Data are presented as the mean + SD, with individual data points overlaid. One‐sample Wilcoxon signed‐rank tests confirmed that VART–VSRT differences…

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  FIGURE 3. Respiratory‐phase modulation of reaction times across conditions and muscles. (a, c, e) Mean reaction times with sinusoidal fits for 1DI, FDS and biceps muscles in the VRT condition. (b, d, f) Individual participant data distributions for the VRT condition. (g, i, k) VART condition means with fits. (h, j, l) Individual participant data distributions for the VART condition. (m, o, q) The VSRT condition means with fits. (n, p, r) Individual participant data distributions for the VSRT condition. Respiratory phases: I1–I3, inspiration; and E1–E3, expiration.

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  FIGURE 4. Respiratory‐phase modulation of the StartReact effect across muscles. (a, c, e) Mean StartReact effect (VART–VSRT difference) with sinusoidal fits for the first dorsal interosseous (1DI; a), flexor digitorum superficialis (FDS; c) and biceps (e) muscles. (b, d, f) Individual participant data distributions showing all VART–VSRT difference values for the corresponding muscles. Significant enhancement of the StartReact effect was observed during respiratory‐phase transitions compared with mid‐phases (1DI, P = 0.037; FDS, P = 0.003; biceps, P = 0.011). Respiratory phases: I1–I3, inspiration; and E1–E3, expiration.