Effects of different exercise intensities on prefrontal activity during a dual task

Abstract

The effects of physical exercise on cognitive tasks have been investigated. However, it is unclear how different exercise intensities affect the neural activity. In this study, we investigated the neural activity in the prefrontal cortex (PFC) by varying the exercise intensity while participants performed a dual task (DT). Twenty healthy young adults performed serial subtraction while driving a cycle ergometer. Exercise intensity was set to one of three levels: low, moderate, or high intensity. We did not find any significant change in PFC activity during DT under either the control (no exercise) or low-intensity conditions. In contrast, we observed a significant increase in PFC activity during DT under moderate- and high-intensity conditions. In addition, we observed complex hemodynamics after DT. PFC activity decreased from baseline after DT under the control condition, while it increased under the low-intensity condition. PFC activity remained higher than the baseline level after DT under the moderate-intensity condition but returned to baseline under the high-intensity condition. The results suggest that moderate-intensity exercise with a cognitive load effectively increases PFC activity, and low-intensity exercise may increase PFC activity when combined with a cognitive load.

Figure 1

NIRS channel layout. The red circles indicate the emitter probes, and the blue circles indicate the detector probes. Each number indicates the channel number.

Figure 2

Topographical maps of PFC activation under control, low-intensity, moderate-intensity, and high-intensity conditions. The circles represent channels, the locations of which correspond to the channels shown in Fig. 1. The color bar indicates the t-value, which indicates the increase or decrease in oxy-Hb concentration from the resting period. The bluish color indicates the decrease in oxy-Hb concentration during the task (M1, DT, and M2) relative to the resting period, whereas the reddish color indicates the increase. The channel with a significant difference is outlined with a thicker black circle (p < .05). We separately analyzed the concentration of oxy-Hb during the first and second halves of M1, DT, and M2. The upper panels of each of the periods M1, DT, and M2 in the figure show the results of the first half and the lower panels show those of the second half.

Figure 3

Normalized mean oxy-Hb concentration during the task for each exercise intensity. The oxy-Hb concentration was normalized by that in the resting period and averaged for each exercise intensity. Mean ± SEM. *A significant difference between the task conditions (p < .05). ^†A significant difference from under the rest condition (p < .05).