Modulation of sensorimotor mu-rhythm during combined motor imagery and sustained muscle contraction

Event-related desynchronization (ERD) of the mu-rhythm during motor imagery (MI) is widely used in brain-computer interfaces (BCIs). Yet, the combination of MI with different types of motor activities needs to be further clarified. Here we investigated how sustained voluntary muscle contraction interferes with MI. Fifteen volunteers participated in the experiment which consisted of six tasks: rhythmic squeezing of a tennis ball, sustained muscle contraction, MI of rhythmic squeezing, and MI combined with sustained contraction of the same/opposite/both hands. The results showed that: (1) ERD was stronger during physical movements compared to MI. (2) Sustained muscle contraction, but not rhythmic contraction caused mu-rhythm desynchronization in the contralateral hemisphere. (3) ERD increased when MI was combined with sustained contraction of the opposite hand. These findings demonstrate that sustained muscle contraction modifies the manifestation of MI in the sensorimotor cortex activity. As such, the explored combinations of tasks could be utilized in BCI research and clinical practice.