Illuminating the developing brain: the past, present and future of functional near infrared spectroscopy.

A decade has passed since near infrared spectroscopy (NIRS) was first applied to functional brain imaging in infants. As part of the team that published the first functional near infrared spectroscopy (fNIRS) infant study in 1998, we have continued to develop and refine both the technology and methods associated with these measurements. The increasing international interest that this technology is generating among neurodevelopmental researchers and the recent technical developments in biomedical optics have prompted us to compile this review of the challenges that have been overcome in this field, and the practicalities of performing fNIRS in infants. We highlight the increasingly diverse and ambitious studies that have been undertaken and review the technological and methodological advances that have been made in the study design, optical probe development, and interpretation and analyses of the haemodynamic response. A strong emphasis is placed on the potential of the technology and future prospects of fNIRS in the field of developmental neuroscience.