Study Of Cognitive Mechanisms Of Mental Rotation Task Between Endogenous And Exogenous Strategy

Mental rotation is a psychological process which subject compares two similar objects at different orientations in mind. With the quantitative mental load in aspect of orientation difference, mental rotation task was widely used in studies of motor imagery and motor disability. Considerable studies have examined the participation of motor-related areas in the process of mental rotation. However, the cortical activation in different studies are not all consistent, which might be attributed to different stimuli characteristics(vital/tools or abstract objects) and rotation strategies(endogenous/exogenous). In addition, although the judge of the stimulus parity has been popularly used in mental rotation task, the cognitive difference between identical and mirrored stimuli has not well investigated. In summary, the mechanism of mental rotation is not yet clear.To reveal the possible influence of rotating strategy and the effect of stimulus parity in the time course of mental rotation, we studied the behavior response and beta band event-related de-/synchronization(ERD/ERS) in a mental rotation task, i.e., comparing one object to its identical or mirror-rotated counterpart, with participates randomly divided into two groups performing the task by the strategies of exogenous force(n=16, denoted as EX hereafter) and endogenous force(n=13, denoted as EN hereafter) respectively.ERD/ERS results showed a sharp desynchronization(ERD) at 150~300 ms. The duration of this ERD increased with rotation angle. Rotating angle showed significant main effect in parietal area, fronto-parietal area and central cortex at late phases of mental rotation. We observed that the cognitive model of two strategies differed in early and medium stages of rotation. This discrepancy occurred mainly in the left prefrontal area, which is highly correlated with endogenous guided motor processing, indicating that the endogenous force group had been preparing for motor simulation. In contrast to the fast rebound of ERD/ERS in the case of identical 0°, the ERD/ERS in mirrored 0° showed similar results with the rotated mirrored ones. Considering the brain areas in which ERD showed a significant main effect of parity, we concluded that subject tends to flip the mirrored object into identical representation additionally to the rotation process.