In biomedical translational research for development of new and better therapeutic treatments of neurodevelopmental and psychiatric disorders, animal model studies are essential. Nevertheless, problems are often raised in such translational research due to difference of experimental techniques or approach used between animals and humans, which make difficult to bring findings in animal studies into human clinical conditions. Therefore, it is important to find reliable biomarkers that can be measured equally both in animal models and human patients. To address this issue, we developed the method to measure cortical neural activity using Near-infrared spectroscpy (NIRS) in Japanese macaques. Because of its relative easiness of use and safety, which enables applicable to small children and even infants, NIRS has been now widely used both in human basic and clinical research. Conducting cortical acttivity measurement using NIRS in non-human primates enables to directly compare cortical activity in humans including small children, and thereby contributes finding biomarkers for psychiatric disorders such as schizophrenia and autism. Moreover, given the advantage of invasive approach allowed in primates, we are currently investigating several problems that NIRS faces such as inclusion of noise signals from skull skin into cortical activity measurement by conducting NIRS in animals with and without skull skin.