Neural decoding of gait phase information during motor imagery and improvement of the decoding accuracy by concurrent action observation

Brain decoding of motor imagery (MI) is crucial for the control of neuroprosthesis, and it provides insights into the underlying neural mechanisms. Walking consists of stance and swing phases, which are associated with different biomechanical and neural control features. However, previous studies on the decoding of the MI of walking focused on the classification of more simple information (e.g., walk and rest). Here, we investigated the feasibility of electroencephalogram (EEG) decoding of the two gait phases during the MI of walking and whether the combined use of MI and action observation (AO) would improve decoding accuracy. We demonstrated that the stance and swing phases could be decoded from EEGs during AO or MI alone. Additionally, the combined use of MI and AO improved decoding accuracy. The decoding models indicated that the improved decoding accuracy following the combined use of MI and AO was facilitated by the additional information resulting from the concurrent cortical activations by multiple regions associated with MI and AO. This study is the first to show that decoding the stance versus swing phases during MI is feasible. The current findings provide fundamental knowledge for neuroprosthetic design and gait rehabilitation, and they expand our understanding of the neural activity underlying AO, MI, and AO+MI of walking.