The effect of changes in cerebral blood flow on cognitive function during exercise

Abstract

No studies have identified the direct effect of changes in cerebral blood flow (CBF) on cognitive function at rest and during exercise. In this study, we manipulated CBF using hypercapnic gas to examine whether an increase in CBF improves cognitive function during prolonged exercise. The speed and the accuracy of cognitive function were assessed using the Stroop color-word test. After the Stroop test at rest, the subjects began exercising on a cycling ergometer in which the workload was increased by 0.5 kilopond every minute until a target heart rate of 140 beats/min was achieved. Then, the subjects continued to cycle at a constant rate for 50 min. At four time points during the exercise (0, 10, 20, 50 min), the subjects performed a Stroop test with and without hypercapnic respiratory gas (2.0% CO2), with a random order of the exposures in the two tests. Despite a decrease in the mean blood flow velocity in the middle cerebral artery (MCA Vmean), the reaction time for the Stroop test gradually decreased during the prolonged exercise without any loss of performance accuracy. In addition, the hypercapnia-induced increase in MCA Vmean produced neither changes in the reaction time nor error in the Stroop test during exercise. These findings suggest that the changes in CBF are unlikely to affect cognitive function during prolonged exercise. Thus, we conclude that improved cognitive function may be due to cerebral neural activation associated with exercise rather than global cerebral circulatory condition.

Keywords: arterial blood pressure; brain; cognition; humans; hypercapnia.

© 2014 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.

Figures

Figure 1.

(A) Experimental protocol. (B) An example of randomized incongruent words and colors‐recognition tests. The example indicates that the word is blue (underlined) while it is printed in red, and then the subjects have to press “blue” key and not “red” key.

Figure 2.

Cognitive function improved during prolonged exercise despite decreases in CBF. (A) MCA mean blood flow velocity (MCA Vmean), (B) reaction time, (C) performance accuracy at rest, and during prolonged exercise. The values shown represent the mean ± SEM. *P < 0.05, **P < 0.01 between the groups.

Figure 3.

Hypercapnia‐induced increase in CBF did not affect cognitive function at rest as well as any time point during the prolonged exercise. (A) Changes in MCA mean blood flow velocity (ΔMCA Vmean) in response to hypercapnic stimulation at rest and during exercise. Hypercapnic stimulation significantly increased the MCA Vmean at each time point (P < 0.01). Changes in (B) reaction time (Δreaction time), (C) performance accuracy (Δperformance accuracy) in response to hypercapnic stimulation at rest and during exercise. Hypercapnic stimulation did not change reaction time and performance accuracy. The values shown represent the mean ± SEM.