A role for near infrared spectroscopy in psychiatry?

Present implementations of near infrared spectroscopy permit the detection of signals related to neuronal activity non-invasively through the intact skull (for review see: Chance, 1991). Due to the limited penetration of photons in soft tissue that is in the range of a few centimeters (Chance et al., 1993), the NIRS field of view is restricted to the outer cerebral cortex in the human adult (Villringer K et al., this issue). Activation-induced changes in regional cerebral endogenous chromophore concentrations (oxygenated [HbO2] and reduced [HbR] hemoglobin, as well as total hemoglobin [HbT]) have been demonstrated during the performance of either cognitive tasks (Hoshi et al., 1993a; Villringer et al., 1993) or visual (Kato et al., 1993) and motor stimulation (Obrig et al., 1996). As cognitive disturbances occur in a variety of psychiatric disorders, such as dementia, depression, schizophrenia and substance abuse, NIRS may help to detect disease- or syndrome-specific alterations that may be either of diagnostic value and/or useful for therapeutic monitoring. So far, activation-induced changes in NIRS variables have been demonstrated during normal aging (Hock et al., 1995a), dementia (Hock et al., 1995b) and schizophrenia (Okada et al., 1994). However, in view of the powerful neuroimaging methods such as magnetic resonance imaging (MRI), functional MRI (fMRI) and positron emission tomography (PET), one has to ask for the specific advantages of the NIRS method, that is in the adult, so far, only in experimental use. Although at the moment inferior to PET with regard to spatial as well as to fMRI with regard to spatial and temporal resolution, NIRS has an interesting potential: the method requires neither large expensive equipment nor an exogenous contrast medium, unlike PET or MRI.