Reduction of low-frequency oscillations in cerebral circulation correlates with pupil dilation during cognition: an fNIRS study

Numerous studies have utilized functional near-infrared spectroscopy (fNIRS) to investigate brain hemodynamics during diverse cognitive tasks. However, although these studies have consistently reported increased oxygenation levels in the prefrontal cortex, they have not explored their effects on the amplitude of brain low-frequency oscillations (LFO). Additionally, other reports have shown that pupil dilation occurs during cognitive tasks, which may indicate a correlation between LFO amplitude and pupil dilation. However, no study has demonstrated such a correlation. Our research has two aims: firstly, to analyze the impact of cognitive tasks on the amplitude of LFO using oxyhemoglobin (HbO2) fNIRS signals, and secondly, to assess the relationship between the amplitude of these LFO and pupil diameters during such cognitive tasks. We found that during arithmetic tasks, the brain LFOs recorded on the prefrontal cortex were temporarily reduced while pupil diameter increased. These findings offer new insights into the physiological functions of reactivity of LFO in cerebral circulation. Additionally, combining fNIRS signals to track LFO on the prefrontal cortex with pupil measurement shows the feasibility of developing efficient hybrid brain-computer interfaces of LFO-pupil detection capable of predicting the initiation and ending of cognitive processes. Significant statementInspired by the Berger effect, which demonstrates alpha wave reactivity with eye-opening, our study investigated reactivity in other physiological oscillations related to brain hemodynamics during cognition. Our findings revealed a novel phenomenon: a temporary reduction in the amplitude of low-frequency oscillations (LFOs) of oxyhemoglobin (HbO2) in the brains prefrontal cortex, concurrent with increased pupil diameter during arithmetic tasks. This discovery expands our knowledge of LFO in cerebral circulation and creates new avenues for studying fNIRS-LFO reactivity during cognitive tasks in healthy individuals and patients.