Abstract
Near-infrared spectroscopy (NIRS) has been largely used in neuroscience as an alternative non-invasive neuroimaging technique, primarily to measure the oxygenation levels of cerebral haemoglobin. Its portability and relative robustness against motion artefacts made it an ideal method to measure cerebral blood changes during physical activity. Usually referred to as 'functional' NIRS (fNIRS) when used to monitor brain changes during motor or cognitive tasks, this technique often involves the montage the probes on the forehead of the participants to gauge the neurophysiological underpinning of executive functioning. Other applications of NIRS include other aspects of cerebral hemodynamics such as cerebral pulsatility. However, there is an important aspect that fNIRS studies do not seem to have taken into account so far, which relates to the capacity of near-infrared light to modulate cognitive and psychological processes according to what is known as photobiomodulation (PBM). Hence, drawing on a selection of NIRS and PBM experiments, we argue in favour of an integrative view for NIR-based neuroimaging studies, which should embrace a control for the possible effects of light stimulation, especially when fNIRS is considered to test the effect of an intervention.
Highlights
Brain research based on non-invasive light-emitting probes has seen its start in the Seventies [1] and since this technology has been used in several experiments and applications. This commentary will refer to the different uses of near-infrared light technology, either near-infrared spectroscopy (NIRS) or photobiomodulation (PBM), hinting at a possible functional overlap of the two
We will revise a series of studies about the effects of physical activity on the brain and behavioral outcomes, arguing that there might be a possible extra effect operated by NIRS itself, which has been uncontrolled
Further evidence in favor of the positive effect of physical activity on cognition and brain activity was provided by other NIRS studies, where it was found that: NIRS-derived prefrontal cortical hemodynamics are influenced by exercise intensity, age of participants and type of cognitive task [31]; activity in prefrontal cortex (PFC) is progressively enhanced during increasing levels of exercise [32]; high-fit older women show significant increases in the cortical right PFC activations as a function of task difficulty compared to low-fit group [33]; the right inferior frontal gyrus is activated during neuropsychological testing only in high fit women [34]; a continuous rather than an intermittent type of exercise can lead to a higher cortical oxygenation level and a better performance at the Stroop tasks compared to pre-exercise indices [35]
Summary
Brain research based on non-invasive light-emitting probes has seen its start in the Seventies [1] and since this technology has been used in several experiments and applications. This commentary will refer to the different uses of near-infrared light technology, either NIRS or photobiomodulation (PBM), hinting at a possible functional overlap of the two. We will revise a series of studies about the effects of physical activity on the brain and behavioral outcomes, arguing that there might be a possible extra effect operated by NIRS itself, which has been uncontrolled
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