Once consent is provided, subjects will undergo a MI-BCI usability session, they will be seated comfortably in front of a computer screen. An EEG cap will be comfortably worn over the head of the subject to record EEG traces of any activated cortical areas. Subjects will then be instructed to perform a mental imagery task whereby they will imagine themselves walking properly with their affected leg. The accuracies in classifying correct motor imagery from the idle condition from EEG will be recorded for each subject. Subjects who obtain an accuracy of more than 57.5% are considered eligible for the MI-BCI training program. Subjects eligible for the MI-BCI training will then undergo a series of functional assessments, including (1) functional clinical measures (10 meter walk test and Up-to-Go test), (2) gait analysis , (3) cortical activity assessment using TMS, and (4) MRI and DTI scan. (5) Psychological tests including Beck Depression Inventory, fatigue severity scale, digital span test. Before the start of MI-BCI training, subjects will undergo one more MI-BCI session of calibration, which will be performed totally the same with BCI usability session to gather more valuable data for analyzing. After finishing all 5 assessments and MI-BCI calibration session, the MI-BCI training can be started at the frequency of 3 times a week lasting for 4 weeks. The procedure of MI-BCI training is identical to the one in BCI usability session except that a cartoon character in the computer screen will be activated to walk forward if subjects successfully perform an accurate mental imagery. Subjects undergoing MI-BCI training will be required to perform 160 trials of MI altogether with assigned rest periods (5 mins) every 40 trials. Each session will last approximate 45 minutes excluding set-up time. The number of times subjects can successfully perform the MI task and the ease in which they are able to perform the task will be recorded. Distinct brain signals such as event-related desynchronization or synchronization (ERD/ERS) are detectable on EEG for both real and imagined motor movements in healthy subjects. Using this technique, MI-BCI, which translates the imagination of movements into online commands, provides a promising neural communication system for stroke patients who suffer from motor disabilities. We have previously collaborated with I2R-A*STAR BCI to design a custom-built BCI software to sync with an EEG amplifier. We have demonstrated the efficacy of this custom-built MI-BCI device on upper limb stroke impairments, therefore, the procedure and equipment used will be kept identical except for the software interface, which shows a cartoon character on the screen. Subjects will undergo the same five assessments again at the end of the 4-week's MI-BCI training and 4-6 weeks after the last session of MI-BCI training, respectively, including (1) functional clinical outcome measures (10 meter walk test and Up-to-Go test), (2) gait analysis, (3) cortical activity assessment using TMS, and (4) MRI and DTI. (5) Psychological tests including Beck Depression Inventory, fatigue severity scale, digital span test.