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Objective Motor impairment is one of the major disabilities in stroke patients.A variety of methods for improving motor functions have been proposed so far, among which, mental practice-based training, e.g.motor imagery (MI), has been promising one and gaining more attention in the rehabilitation of stroke over last decade.MI has been proved effective in stroke recovery when subjects only imagine body actions without true executions.However, MI is difficult to assess as a covert active process in working memory without overt output.Nevertheless, tMRI studies have revealed the involvement of BA4, supplementary motor areas (SMA), dorsal premotor, primary motor cortex (M1), and etc.in MI, which were considered as the prime targets of post-stroke rehabilitation.One example of MI, mental rotation task (MRT), has been successfully used in stroke patients.In this study, we further investigate the different roles of four cognitive sub-stages in MRT (i.e.).(i) stimulus perceptual encoding (identification of stimuli and its orientation), (ii) mental rotation itself, (iii) parity judgment, (iv) response selection and execution) in stroke rehabilitation by behavior and electroneurophysiologic methods.Methods Fourteen stroke patients and twelve age-matched healthy control subjects participated in this study with written informed consents.During the MRT experiment, pictures of either left or right hand at different orientations were randomly presented.Both behavior (i.e.response time (RT) and accuracy) and EEG/ERP data were simultaneously recorded respectively by E-Prime 2.0 (Psychology Software Tools Inc, Pittsburgh, USA) and Vision Recorder 1.10 (Brain Products GmbH, Gilching, Germany) for each subject.And repeated-measures ANOVA was used for statistical analysis.Results The preliminary results show that RT increased with angle and have the maximum at 180° for both control subjects and stroke patients.Although both groups could accomplish MRT successfully, compared with control subjects, the stroke patients had longer RT (patients vs.control: 4081.68 ± 267.47 ms vs.1317.91 ± 471.66 ms) and lower accurate rate (patients vs.control: 0.83 ± 0.14 vs.0.95 ± 0.03), which indicates that MRT is much more difficult for patients.The difference of RT between stroke patients and control subjects is about 2700 ms (RTstroke-RTcontrot =2700 ms).Furthermore, the RT showed evident "ipsilateral effect", i.e.either left-or right-body-disabled stroke patients responded stower to the stimulus picture with an ipsilateral hand.For ERP results, P200 (160-280 ms post-stimulus presentation) and P300 (280-700ms post-stimulus presentation) components were observed at frontal, central and parietal areas in both groups.Significant "amplitude modulation effect", i.e.the P300 amplitude decreases with the increase of orientation angle, at Fz, Fcl, Fc2, Cz, Cpl, Cp2, P4, Pz etc loci was observed in control subjects but not in patients.Significant delayed latencies of P200 and P300 were observed in stroke patients during MRT (P200 latency: 224 ± 0.36 vs.208 ± 0.36 ms, F =847.358, P =0.000; P300 latency: 437 ± 4.48 vs.423.583 ± 4.48 ms, F =4.813, P =0.039).Previous electroneurophysiologic studies reported that the first three sub-stages were related with P200 and P300 components.Therefore, the latency difference (i.e.~20 ms) of ERP components within 700 ms post stimulus are supposed to be attributed to the first three sub-stages.However, our behavior results showed a much longer RT (i.e.~2700 ms) in the stroke group.Therefore, the last sub-stage of the MRT (i.e.response selection and execution) was supposed to be major cause of such a longer RT in stroke subjects.Conclusion Stroke patients could perceptually encode and complete the MRT successfully.However, the stroke could significantly delay the MRT by impairing the motor selection and execution sub-stages in cognitive process of mental rotation.We therefore suggest that the motor selection and execution might be the critical sub-stage in mental practice training.