LAPLACIAN ERPS FOR PREPARATION TO IMAGINE A LEARNED MOTOR SEQUENCE

In a RT task, event-related Laplacians were estimated in 12 subjects d uring the performance of a simple motor sequence consisting of either an actual or imagined execution of the sequence. The preparatory signa l (precue) alerted the subject to either prepare to execute, or to ima gine an interval of either 700 or 2500 ms, delimited by two thumb pres ses that could be either weak or strong. The precue provided advance i nformation about either the force of thumb presses, the duration of th e interval, neither, or both. During the 3 seconds preparatory period, a CNV developed that had nearly the same time-course for the imaging as for the execution trials. However, the final stage of the CNV over the supplementary motor area (SMA) had twice the amplitude before the execution production than before the imaging simulation of a sequence. According to the variations in CNV amplitude, the hand area of the co ntralateral primary motor cortex appears to be sensitive to the advanc e information in the precue. This sensitivity is obvious during prepar ation for execution, but not during preparation for imaging. Furthermo re, at the end of imagined interval, as well as at the end of the exec uted sequence, the vertex negativity reached a maximum around the time of the second press of the sequence. The similarity of those negative shifts provides a strong argument in favor of identical timing for si mulated and actual performance.