Author(s): ROOSE, M., DE WACHTER, J., PROOST, M., HABAY, J., VERSTRAELEN, M., DE PAUW, K., MEEUSEN, R., ROELANDS, B., Institution: VRIJE UNIVERSITEIT BRUSSEL, Country: BELGIUM, Abstract-ID: 1906

INTRODUCTION:
Mental fatigue (MF) arises from extended periods of demanding cognitive activity and impairs cognitive and physical performance [1]. Hypoxia is another stressor known for impairing performance. Typically, changes in cognitive and physical functioning at altitude are associated with alterations in brain oxygenation [2]. These changes are preferably measured in the prefrontal cortex (PFC), renowned for its role in higher-level cognitive function [2]. Therefore, we aim to examine whether oxygenation of the PFC plays a role in the development of MF.
METHODS:
Twelve participants (age 22.9 ± 3.5 y; height 174.2 ± 8.2 cm; mass 69.9 ± 13.9 kg) completed four experimental trials, 1) MF in (normobaric) hypoxia (3.800m; 13.5%O2), 2) MF in normoxia (98m; 21.0%O2), 3) Control task in hypoxia 4) Control task in normoxia. Participants performed a 2-back task, Digit Symbol Substitution test and Psychomotor Vigilance task before and after a 60-min Stroop task or an emotionally neutral documentary. Brain oxygenation was measured through functional Near Infrared Spectroscopy. Subjective feelings of MF and physiological measures (heart rate, oxygen saturation, blood glucose and hemoglobin) were recorded. A 2 x 2 x 5 three-way repeated-measures ANOVA [Mental State (MF, CON) X FIO2 (normoxia, hypoxia) X Time (baseline, block 1, block 2, block 3, block4)] was used for the MVAS, fNIRS and Stroop task ACC and -RT. For data from the 2BACK, DSST, PVT, SaO2 Mood and BVAS, a 2 x 2 x 2 three-way repeated-measures ANOVA [Mental State (MF, CON) * FIO2 (normoxia, hypoxia) * Time (pre, post)] was performed.
RESULTS:
The Stroop task resulted in increased subjective feelings of MF (F(1.6, 16.2) = 19.3, p < 0.001) compared to watching the documentary (F(1.6, 15.5) = 6.3, p= 0.014). 2-back accuracy was lower post task compared to pre task in MF_NOR and CON_NOR (PRE: 87.1 ± 7.72, POST 75.70 ± 12.88), while no differences were found in the other cognitive tasks. The fraction of inspired oxygen did not impact feelings of MF. Although performing the Stroop resulted in higher subjective feelings of MF, hypoxia had no effect on the severity of self-reported MF. Additionally, no evidence could be provided for a role of oxygenation of the PFC in the build-up of MF.
CONCLUSION:
The role of PFC-oxygenation during the build up to MF and the associated interaction effects with altered oxygen availability were investigated within this study. Although MF was successfully induced, normobaric hypoxia seemed to have no effect on the severity of self-reported MF and subsequent cognitive function. Additionally, no evidence could be provided for the role of PFC oxygenation during a MF task.

References
1. Van Cutsem, J et al. (2017). The Effects of Mental Fatigue on Physical Performance: A Systematic Review. Sports medicine (Auckland, N.Z.), 47(8), 1569-1588.
2. McMorris, T et al. (2017). Effect of acute hypoxia on cognition: A systematic review and meta-regression analysis. Neurosci Biobehav Rev, 74(Pt A), 225-232.