Possible effect of natural light on emotion recognition and the prefrontal cortex: A scoping review of near-infrared (NIR) spectroscopy

Near-infrared (NIR) spectroscopy, also known as functional NIR spectroscopy (fNIRS), is a tool for measuring the hemodynamic response of the prefrontal cortex (PFC) by using NIR light, enabling a noninvasive indirect neural activity assessment. The application of fNIRS in emotion recognition or the differential diagnosis of psychiatric disorders of depressive patients, including major depressive disorder, bipolar disorder and schizophrenia, has previously been reported. Although the use of fNIRS has gradually expanded in cognitive neuroscience studies, few researchers have focused on the effects of light exposure in fNIRS studies. In addition, to the best of our knowledge, there are no scoping reviews of fNIRS studies on light exposure. Because light is an important topic in cognitive neuroscience and psychiatry, we evaluated fNIRS studies on light exposure in humans. We reviewed 10 papers in their entirety. Bright light (BR) modulates fear, and the color differences showed no significance in 1 study, whereas other studies delved extensively into the effects of colored light, finding some individual hemodynamic responses. In our study, we highlighted that the effects of natural light have not been studied using fNIRS. Light is becoming a critical topic in cognitive neuroscience and psychiatry, and fNIRS is critical for improving public health and managing psychiatric disorders.