Functional near-infrared spectroscopy (fNIRS) is an emerging functional neuroimaging technology offering a relatively non-invasive, safe, portable, and low-cost method of indirect and direct monitoring of brain activity. Most exciting is its potential to allow more ecologically valid investigations that can translate laboratory work into more realistic everyday settings and clinical environments. Our aim is to acquaint clinicians and researchers with the unique and beneficial characteristics of fNIRS by reviewing its relative merits and limitations vis-à-vis other brain-imaging technologies such as functional magnetic resonance imaging (fMRI). We review cross-validation work between fMRI and fNIRS, and discuss possible reservations about its deployment in clinical research and practice. Finally, because there is no comprehensive review of applications of fNIRS to brain disorders, we also review findings from the few studies utilizing fNIRS to investigate neurocognitive processes associated with neurological (Alzheimer's disease, Parkinson's disease, epilepsy, traumatic brain injury) and psychiatric disorders (schizophrenia, mood disorders, anxiety disorders).

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Understanding the neurobiological substrates of self-recognition yields important insight into socially and clinically critical cognitive functions such as theory of mind. Experimental evidence suggests that right frontal and parietal lobes preferentially process self-referent information. Recognition of one's own face is an important parameter of self-recognition, but well-controlled experimental data on the brain substrates of self-face recognition is limited. The goal of this study was to characterize the activation specific to self-face in comparison with control conditions of two levels of familiarity: unknown unfamiliar face and the more stringent control of a personally familiar face. We studied 12 healthy volunteers who made "unknown," "familiar," and "self" judgments about photographs of three types of faces: six different novel faces, a personally familiar face (participant's fraternity brother), and their own face during an event-related functional MRI (fMRI) experiment. Contrasting unknown faces with baseline showed activation of the inferior occipital lobe, which supports previous findings suggesting the presence of a generalized face-processing area within the inferior occipital-temporal region. Activation in response to a familiar face, when contrasted with an unknown face, invoked insula, middle temporal, inferior parietal, and medial frontal lobe activation, which is consistent with an existing hypothesis suggesting familiar face recognition taps neural substrates that are different from those involved in general facial processing. Brain response to self-face, when contrasted with familiar face, revealed activation in the right superior frontal gyrus, medial frontal and inferior parietal lobes, and left middle temporal gyrus. The contrast familiar vs. self produced activation only in the anterior cingulate gyrus. Our results support the existence of a bilateral network for both perceptual and executive aspects of self-face processing that cannot be accounted for by a simple hemispheric dominance model. This network is similar to those implicated in social cognition, mirror neuron matching, and face-name matching. Our findings also show that some regions of the medial frontal and parietal lobes are specifically activated by familiar faces but not unknown or self-faces, indicating that these regions may serve as markers of face familiarity and that the differences between activation associated with self-face recognition and familiar face recognition are subtle and appear to be localized to lateral frontal, parietal, and temporal regions. Hum Brain Mapp 27:91-98, 2006.