Reduced cerebral blood flow does not alter concurrent or post-intervention inhibitory control: evidence from a 3-h head-down tilt protocol in healthy young adults.

A transient increase in cerebral blood flow (CBF) via exercise or hypercapnia has-in part-been linked to an executive function (EF) benefit. It is, however, unclear whether a transient reduction in CBF negatively impacts EF. In the present study, healthy young adults (n = 24) completed separate 3-h interventions involving - 12° head-down tilt (HDT) and a control (0°) supine posture. The HDT protocol was used because it induces a cephalad fluid shift that safely and reliably decreases CBF. To estimate CBF, transcranial Doppler ultrasound measured middle cerebral artery velocity (MCAv) at discrete timepoints (i.e., baseline, concurrent with the intervention and recovery) and the Stroop colour-naming task completed at baseline, 30-min intervals throughout the intervention and a recovery timepoint, assessed inhibitory control-based changes in EF. As expected, a time-dependent decrease in MCAv (8%) was observed in the HDT but not the control intervention; however, frequentist and Bayesian statistics demonstrated that Stroop performance metrics were not associated with the MCAv change (ps > 0.12). Instead, time-dependent deficits in Stroop task performance were associated with increased ratings of mental fatigue-a result observed across HDT and control interventions. Accordingly, a reduction in MCAv during a 3-h HDT intervention did not impact an inhibitory control measure of EF and our findings demonstrates neurocognitive resilience during a short-term reduction in CBF.