This paper describes a motion simulator for the lower extremities of human in a magnetic resonance imaging (MRI) environment. The motion simulator provides physical support for a wearer to move his/her lower extremities like gait. The simulator also provides his/her sole contact sensation like floor reactive force during gait. An MRI is one of the most powerful tools to measure brain activity, and requires that a device driven in MRI environment is MRI compatible. This paper shows the MRI compatibility of the simulator which consists of nonmagnetic materials and actuators. We confirm that the simulator does not affect quality of image of MRI adversely when a distance between the simulator and a head coil of the MRI is more than 300[mm]. When MRI measures brain activity of human wearing LoMS, the distance is more than 400[mm]. We also confirm that LoMS can measure own joint angles with potentiometers through simple low-pass filters avoiding noise due to MRI. Then we measure brain activity of a man wearing LoMS during gait-like motion and the brain region related to gait is activated by the motion.
