Relationship Between Kinesthetic/Visual Motor Imagery Difficulty and Event-Related Desynchronization/Synchronization

Motor imagery (MI) is divided into two types: kinesthetic (KMI) and visual (VMI). To estimate the MI that an examinee performs, event-related desynchronization (ERD) or event-related synchronization (ERS) is used to characterize KMI or VMI via electroencephalogram (EEG). However, no definitive method using ERD/ERS via EEG has been established yet to estimate the type of MI performed. This is because the MI performed by the examinee is not always the same as that instructed by the examiner. One of the reasons for this mismatch is the difficulty of MI, especially KMI. However, almost no reported studies have considered MI difficulty to estimate MI type. Therefore, in this study, we examined the relationship between MI difficulty and the ERD/ERS pattern corresponding to the type of MI in the case of single flexion of the right index finger (SFRIF). The results showed that for a subject who felt MI was less difficult, the α-band ERD value (αERD) at the electrode of the occipital area (O1 or O2 site) of the KMI instruction was significantly smaller than that of the VMI instruction. On the contrary, for a subject who felt MI was very difficult, αERD at the O1 or O2 site on the KMI instruction was similar to that of the VMI instruction. In addition, for the subject who felt MI was easy, the αERDs at the O1 or O2 site on the KMI and VMI instructions were similar to those on the movement execution (ME) and movement observation (MO) instructions, respectively. Therefore, in the case of SFRIF, it was suggested that MI difficulty could be estimated by ERD/ERS patterns in the occipital area. This was supported by referring to the ME and MO ERD/ERS patterns in the occipital area.