**2.3 Application of NIRS to human gait control**

Gait requires complex visuo-sensorimotor coordination. Like in other animals, human locomotion is controlled by multiple neural systems, hierarchically distributed throughout the central nervous system, including the spinal cord, brainstem, cerebellum, basal ganglia, and motor cortex (Grillner & Wallen, 2004). Although most studies of neuronal mechanisms of gait control were conducted with quadruped animals, a bipedal stance and gait are unique functions of humans. Therefore, functional imaging studies in humans are important for investigating the neural mechanisms of gait control. However, as stated above, it is difficult to study dynamic movements such as gait control with conventional neuroimaging techniques, and functional NIRS is a suitable tool for these studies.
