Past and future of near-infrared spectroscopy in studies of emotion and social neuroscience

Near-infrared spectroscopy (NIRS) enables the non-invasive measurement of spatiotemporal characteristics of brain function, which has received increasing attention during the last years. This new birth of interest is attributable to unique characteristics of the NIRS technique, which may be summarised in certain technical advantages: its experimental and ecological validity and the extension of application to clinical samples. This paper presents the main applications of the NIRS technique that measures changes in brain activation to study emotions and social neuroscience field. In the first part of this paper, we discuss the basic principles, strengths, and limitations of NIRS for the study of principal emotional functions. In the second part, we focus on the actual applications of NIRS in emotional and social research. In this regard, first, we consider some main topics of emotional contexts, such as visual (facial expression) and auditory cues recognition, and social neuroscience field. Second, we discuss the utility to apply NIRS simultaneously to other techniques (electroencephalography, Transcranial Magnetic Stimulation, and functional Magnetic Resonance Imaging) to improve the intrinsic power of such measures. Third, we consider the possible applications of NIRS devices to study specific emotion-related functions (such as connectivity and plasticity applications).