The medical management and treatment of children with psychosomatic, behavioral, and psychiatric disorders have gained recent attention among pediatricians because of the increased number of such patients visiting outpatient clinics. According to a nationwide epidemiological survey in Japan, 5.8% of all children who visited an outpatient pediatric clinic on a given day were considered to have a psychosomatic or psychosocial disorder [1
]. As most pediatricians are not accustomed to examining these children, the Japanese Society of Psychosomatic Pediatrics has published clinical practice guidelines, which provide recommendations for the assessment, diagnosis, and treatment of pediatric psychosomatic disorders in primary care settings [2
]. However, patient-reported outcome measurements may be required to establish clear evidence-based assessment of the effectiveness of these guidelines. Furthermore, better scientific understanding of the biological mechanisms underlying these disorders would highlight the significant associations between physical symptoms and the mind.
Developmental cognitive neuroscience in children is a rapidly growing research field that seeks to understand how the development of a child's brain is involved in the growth of the child's mind. In particular, advances in functional neuroimaging have revealed how localized cortical activity may be associated with behavioral responses during early human development and the impaired neural substrates in behavioral and cognitive dysfunction observed in child psychosomatic or psychiatric disorders. Over the past 20 years, functional magnetic resonance imaging (fMRI) technology has also greatly enhanced our understanding of developmental cognitive function in working memory and attention [3
], and has revealed aberrant neural activation in adults with cognitive dysfunction such as depression, schizophrenia, and eating disorders [6
]. This functional neuroimaging technique has also been applied to the understanding of developmental specialization for human voice processing, which plays a fundamental role in social communication. Dehaene-Lamberts et al. [8
] discovered that when infants listen to speech in their native language, activation was not distributed widely, but was already concentrated to a set of left-hemispheric perisylvian regions, similar to the situation in human adults. In addition, the brain networks involved in processing non-speech human vocalizations, such as music, and emotionally stimulated vocalization, such as mother's voice, have also been studied using fMRI in early infant brain [9
Near-infrared spectroscopy (NIRS) provides a new direction for developmental cognitive neuroscience research. The application of fMRI to infants is restricted to periods of sleep; however NIRS, a completely noninvasive neuroimaging technique, can be applied in the natural setting in children of any age, even whilst awake. This means that visual stimulation, such as viewing an emotional face, can be applied as a cognitive task while the subject is conscious. While there have been several recent reviews on functional NIRS for developmental cognitive neuroscience studies in adult neuropsychiatric disorders [11
], there have been far fewer on clinical research in children. Due to its portability, NIRS is now being applied in all age groups including children and to various fields of cognitive science. Herein we review the breadth of functional NIRS studies of children who have developed normally and of children with psychosomatic or behavioral disorders.