Near-Infrared Spectroscopy (NIRS) in Functional Research of Prefrontal Cortex

Abstract

Functional near-infrared spectroscopy (fNIRS) uses specific wavelengths of light to provide measures of cerebral oxygenated and deoxygenated hemoglobin that are correlated with the functional magnetic functional imaging (fMRI) BOLD signal. fNIRS has emerged during the last decade as a promising non-invasive neuroimaging tool and has used to monitor various types of brain activities during motor and cognitive tasks with increasing interest from research communities. One can see classical comprehensive reviews of such investigations elsewhere (Hoshi, 2003;Koizumi et al., 2003;Obrig and Villringer, 2003). While various MRI methods documented in the literatures have provided essential information about the brain systems concerning these issues up to the present, they have two major limitations, their requirement for participant immobility and their high operational cost. Particularly, the former rules out the use of such techniques for investigating brain dynamics during every activities such as walking and running. On the other hand, fNIRS can be used under less body constraints than other imaging modalities require. Moreover, it is quiet (no operating sound). Thus, the conditions for performing fNIRS measurements are much more comfortable for human as well as non-human subjects (Wakita et al., 2010). In addition, it provides higher temporal resolution (faster sampling frequency). In this respect, fNIRS is useful for studying brain activity under more "natural" and therefore much more variable conditions though it can only monitor cortical regions with less spatial resolution (usually in the centimeter range).Since fNIRS is a non-invasive, safe and portable method, topics that NIRS researches could address are highly variable, and more diverse than those with other non-invasive imaging research techniques. That fact makes fNIRS an ideal candidate for monitoring activity of prefrontal cortex, which has been undertaken with respect to more broadly based issues across the broad expanse of research communities. In fact, many academic journals in diverse areas publish findings obtained from pioneering fNIRS measurements of prefrontal regions. We must admit that this diversity of fNIRS applications makes difficult to access accumulated experience. Protocols of fNIRS recordings from various investigations are not necessarily well-standardized and not necessarily well-grounded on available knowledge of appropriate fNIRS use. One of the purposes of the current research topic is to address this issue across both theoretical and empirical aspects.In order to realize the high potential of fNIRS, effective discrimination between physiological noise originating from forehead skin hemodynamic and cerebral signals is a pre-requisite. Main sources of physiological noise are global and local blood flow regulation processes on multiple time scales. Having attempted to identify the main physiological noise contributions in fNIRS forehead signals and to develop a method for physiological de-noising of fNIRS data, Kirilina et al. (2013)...