Abstract
Motor imagery (MI), sharing similar neural representations to motor execution, is regarded as a window to investigate the cognitive motor processes. However, in comparison to simple limb motor imagery, significantly less work has been reported on brain oscillatory patterns induced by compound limb motor imagery which involves several parts of limbs. This study aims to investigate differences of the electroencephalogram (EEG) patterns as well as cognitive process between simple limb motor imagery and compound limb motor imagery. Ten subjects participated in the experiment involving three tasks of simple limb motor imagery (left hand, right hand, feet) and three tasks of compound limb motor imagery (both hands, left hand combined with right foot, right hand combined with left foot). Simultaneous imagination of different limbs contributes to the activation of larger cortical areas as well as two estimated sources located at corresponding motor areas within beta rhythm. Compared with simple limb motor imagery, compound limb motor imagery presents a network with more effective interactions overlying larger brain regions, additionally shows significantly larger causal flow over sensorimotor areas and larger causal density over both sensorimotor areas and neighboring regions. On the other hand, compound limb motor imagery also shows significantly larger 10–11 Hz alpha desynchronization at occipital areas and central theta synchronization. Furthermore, the phase-locking value (PLV) between central and occipital areas of left/right hand combined with contralateral foot imagery is significantly larger than that of simple limb motor imagery. All these findings imply that there exist apparent intrinsic distinctions of neural mechanism between simple and compound limb motor imagery, which presents a more complex effective connectivity network and may involve a more complex cognitive process during information processing.
Highlights
Motor imagery (MI), defined as mental rehearsal of a motor act without any overt motor output, can modify the neuronal activity in the primary sensorimotor areas in a very similar way as motor execution [1,2,3]
In order to investigate the differences of the EEG patterns as well as cognitive process between simple limb motor imagery and compound limb motor imagery, seven kinds of mental tasks have been designed, involving three tasks of simple limb motor imagery, three tasks of compound limb motor imagery combining hand with hand/foot and rest state
From the distribution during left/right hand combined with contralateral foot imagery, we can see larger involved areas with strong event-related desynchronization (ERD) including contralateral hand area and midcentral area, which is obviously distinct from the distribution of simple limb motor imagery
Summary
Motor imagery (MI), defined as mental rehearsal of a motor act without any overt motor output, can modify the neuronal activity in the primary sensorimotor areas in a very similar way as motor execution [1,2,3]. Motor imagery can result in frequency specific changes of the ongoing EEG in forms of event-related desynchronization (ERD) or eventrelated synchronization (ERS), and the neural representations during mental tasks could be detected using spatial mapping of ERD/ERS. There is a growing concern for interactions of the activated brain regions, typically in terms of ‘‘effective connectivity’’ [5]. Effective connectivity is a powerful method to analyze causal interaction among multiple neural regions in brain studies based on brain imaging techniques such as electroencephalogram (EEG)
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