Improved cerebral oxygenation response and executive performance as a function of cardiorespiratory fitness in older women: a fNIRS study

Abstract

Cardiorespiratory fitness has been shown to protect and enhance cognitive and brain functions, but little is known about the cortical mechanisms that underlie these changes in older adults. In this study, functional near infrared spectroscopy (fNIRS) was used to investigate variations in oxyhemoglobin [HbO2] and in deoxyhemoglobin [HHb] in the dorsolateral prefrontal cortex (DLPFC) during the performance of an executive control task in older women with different levels of cardiorespiratory fitness (VO2max). Thirty-four women aged 60-77 years were classified as high-fit and low-fit based on VO2max measures. They all performed a control counting (CNT) task and the Random Number Generation (RNG) task at two different paces (1 number/1 s and 1 number/1.5 s), allowing to manipulate task difficulty, while hemodynamic responses in the bilateral DLPFCs were recorded using continuous-wave NIRS. The behavioral data revealed that the high-fit women showed significantly better performance on the RNG tasks compared with the low-fit women. The high-fit women showed significant increases in [HbO2] responses in both left and right DLPFCs during the RNG task, while the low-fit women showed significantly less activation in the right DLPFC compared with the right DLPFC of the high-fit women and compared with their own left DLPFC. At the level of the whole sample, increases in the [HbO2] responses in the right DLPFC were found to mediate in part the relationship between VO2max level and executive performance during the RNG task at 1.5 s but not at 1 s. These results provide support for the cardiorespiratory fitness hypothesis and suggest that higher levels of aerobic fitness in older women are related to increased cerebral oxygen supply to the DLPFC, sustaining better cognitive performance.

Keywords: aerobic fitness; aging; executive functions; functional near-infrared spectroscopy (fNIRS); prefrontal cortex.

Figure 1

Experimental protocol. Upper: schema of the entire session. After the familiarization period, the participants alternated blocks of RNG tasks and count (CNT) tasks at the slow or fast pace in a counterbalanced order. [HbO₂] and [HHb] concentrations were continuously monitored during the entire protocol using functional near-infrared spectroscopy (fNIRS). Lower: illustration of the fast pace condition. The participants performed two RNG trials alternating with rest periods and count trials in an ABBA vs. BAAB (A = RNG; B = CNT) counterbalanced order across the participants.

Figure 2

Mean Adjacency score (in %) as a function of group and pace. Bars represent standard-errors. *p < 0.05.

Figure 3

Illustration of typical cortical activation patterns for one subject as a function of task (CNT task, upper side vs. RNG task, lower side), trial and pace (slow vs. fast) for both hemispheres (right DLPFC, left panel and left DLPFC, right panel). Each curve represents one trial with [HbO₂] in red and [HHb] in blue. CNT = Count task; RNG = Random Number Generation task.

Figure 4

Mean Δ[HbO₂] slope coefficients (in red) and mean Δ[HHb] slope coefficients (in blue) in μM.cm/s during the CNT task (A) and the RNG task (B) for the Low-fit group and the High-fit group in the Left DLPFC (left panel) and in the Right DLPFC (right panel). Bars represent standard-errors. *p < 0.05.

Figure 5

Relationships between the VO₂max level, the Δ[HbO₂] slope coefficient in the right DLPFC during the 1.5 s RNG task and the Adjacency score at 1.5 s. r_p: partial correlation after controlling for the 1.5 Δ[HbO₂] slope coefficient in the right DLPFC.