Evidence for unconscious regulation of performance in fatigue

Figures

• 

  Figure 1. Experimental design. (A) The study was performed on two consecutive days. The experiment on the first day (day 1) consisted of an MEG session (MEG session 1), and a hand-grip session and that on the second day (day 2) consisted of an MEG session (MEG session 2) identical to that on day 1. In the MEG sessions, the participants were instructed to perform the target and control tasks. Just before and after the target, control, and hand-grip tasks, the participants were asked to rate their subjective level of fatigue using a visual analogue scale (VAS) and grip strength (GS) was assessed. At the end of the experiment on day 2, they were asked whether they recognized the existence of the target marks during the hand-grip task performed on day 1. (B) In the target task, they were asked to view an image, which was the repetition of a fixation cross for 1300 to 1700 ms followed by a target mark for 2500 ms (the target mark is a closed triangle in this figure). The target mark was presented 180 times. (C) In the control task, participants were asked to view another image, which was the repetition of a fixation cross for 1300 to 1700 ms followed by a control mark for 2500 ms (the control…

• 

  Figure 2. Subjective level of fatigue. The increases in the subjective level of fatigue during the control and target tasks in MEG session 1 (A), the levels of fatigue sensation before and after the hand-grip session (B), and the increases in the subjective level of fatigue during the control and target tasks in MEG session 2 (C) were shown. Participants were asked to rate their subjective level of fatigue on a 100-mm visual analogue scale (VAS) ranging from 0 (minimum fatigue) to 100 (maximum fatigue). Data are presented as means and standard deviations. **P < 0.01, paired t-test.

• 

  Figure 3. Grip strength. Grip strength assessed before and after the control and target tasks in MEG session 1 (A), that assessed before and after the hand-grip task (B), and that assessed before and after the control and target tasks in MEG session 2 (C) were shown. Data are presented as means and standard deviations. * P < 0.05 and ** P < 0.01, paired t-test.

• 

  Figure 4. Autonomic nerve activity evaluated using frequency domain analysis of R-R wave intervals measured with electrocardiography. Values were transformed by natural logarithm (ln). High frequency power (ln HF, closed columns) and the LF/HF ratio (ln LF/HF; open columns) on day 1 (A) and day 2 (B) are shown. Data are presented as means and standard deviations. # P < 0.10, paired t-test with Bonferroni correction.

• 

  Figure 5. Statistical parametric map. Statistical parametric map of the brain region where the level of increased beta band (13–25 Hz) power was higher in the target task than that in the control task on day 2 is shown (maximum intensity projection). Random-effect analyses of 15 participants, P < 0.05, family-wise-error corrected for the entire search volume.

• 

  Figure 6. Relationship between the decrease in grip strength and the increment of increased beta (13–25 Hz) band power. Relationship between the decrease in grip strength induced by the hand-grip task on day 1 and the increment of increased beta band power in the target task compared with the control task on day 2 is shown. The linear regression line, Pearson’s correlation coefficient, and P value are shown.