Brain oxygenation during cognitive processing is altered with 60 days bedridden inactivity

Regular physical activity elicits central angiogenesis and neurogenesis and may, thus, support cognitive performance and brain health. Training interventions have shown to decrease neuronal activity (decreased hemodynamic response) during executive cognitive processing in prefrontal areas, which is suggested to reflect more efficient information processing (Voelker-Rehage, Godde & Staudinger, 2011). Studies investigating adverse effects of physical inactivity are scarce due to ethical concerns and mainly include injured individuals or observational data. Investigating the effects of inactivity on healthy subjects, however, would provide important information about the timely onset of degradation processes. 60-day bedrest is hypothesized to impair information processing compensated by increased neuronal activity (=higher oxygenated (O2Hb) and lower deoxygenated hemoglobin (HHb) concentrations assessed by functional near-infrared spectroscopy (fNIRS)).

24 participants (aged 33.3 ± 8.9 years, 8 females) spent 60 consecutive days in strict bedrest (group BED). fNIRS (Oxymon, Artinis, Netherlands) was used to monitor hemodynamic changes within the prefrontal cortex at rest and during attentional cognitive tasks (auditory and visual tasks) on day -2 before, 3, 50 during, and +2 and +13 after bedrest. A control group (CTRL, n= 9, aged 32.5 ± 10.0 years, 3 females) completed the same test battery without bedrest. ANOVA for repeated measures with the factors time, group and their interaction were calculated for O2Hb and HHb, as well as reaction time (RT) and accuracy (ACC) of the cognitive tests. Bonferroni test was used for post-hoc pairwise comparisons.

RT was faster for auditory than visual tasks (p< .001). RT revealed a main effect of time (p< .001), but BED and CTRL groups tend to differ in their progressions (time*group p= .045) and only CTRLs showed a significant decrease on day +13 compared to -2 (p= 014). ACC did not change over time, between groups or conditions. For O2Hb, the time*group interaction (p< .001) indicated higher relative prefrontal O2Hb concentration during attentional processing on day 50 of bedrest compared to day -2 (p= .001) and to day +13 after bedrest (p= .033) within the BED group and compared to day 50 of the CTRL group (p= .026). A tendency for higher O2Hb during visual tasks compared to auditory tasks was found (p= .051). No difference was observed for HHb.

Performance in attentional cognitive tasks was slightly affected during 60 days of bedrest. These cognitive deteriorations during bedrest may be reflected by increased O2Hb concentration (higher neuronal/oxygen demand) during cognitive task performance. The adverse effects of physical inactivity were recovered on hemodynamic level two days after bedrest, but remained on behavioral level even thirteen days after bedrest. This may indicate that hemodynamic alterations are not the cause but consequence of cognitive impairments.