Changes in Cerebral Oxygenation and Systemic Physiology During a Verbal Fluency Task: Differences Between Men and Women

Abstract

Background: Sex differences in behavioural performance of a cognitive task have been repeatedly reported in the literature. Whether such differences are also relevant for evoked cerebral haemodynamic and oxygenation responses as well as systemic physiological changes is a topic of ongoing investigations. Aim: We investigated whether changes in cerebral oxygenation and systemic physiological activity are sex-dependent during a verbal fluency task (VFT). Subjects and methods: VFT performance and changes in cerebral oxygenation and systemic physiology were investigated in 32 healthy right-handed adults (17 females, 15 males, age: 25.5 ± 4.3 years). The total duration of the VFT was 9 min. During this phase, subjects were also exposed to blue light (peak wavelength: 450 nm, illuminance: 120 lux). Before and after the VFT, subjects were in darkness. In this study, we used the systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) approach. Absolute concentration changes of oxyhaemoglobin ([O₂Hb]), deoxyhaemoglobin ([HHb]), total haemoglobin ([tHb]), as well as tissue oxygen saturation (StO₂) were measured bilaterally over the prefrontal cortex (PFC) and visual cortex (VC). Systemic physiological parameters were also recorded in parallel (e.g., end-tidal CO₂, heart rate, respiration rate, skin conductance). Results: We found that: (i) Females were better VFT performers in comparison to males. (ii) Changes in [O₂Hb] and [HHb] in the VC were higher for males compared to females during the VFT under blue light exposure. (iii) Lower and higher StO₂ changes were detected for males compared to females in the PFC and VC, respectively. (iv) Sex-dependent changes were also evident for end-tidal CO₂, heart rate, respiration rate, and pulse-respiration quotient. Conclusions: Our study showed that sex differences are not only observed in task performance but also in the magnitudes of changes in cerebral and physiological parameters. The findings of the current study emphasise that sex differences in brain activation and systemic physiological activity need to be considered when interpreting functional neuroimaging data. These findings offer a broad range of implications for educational purposes and facilitate a better understanding of the effects of sex on behavioural performance as well as human physiology.