Figure 1.

(A) Instructed-delay choice reaction time (RT) task: subjects were required to perform left or right index finger key-presses (F12 or F5 keyboard buttons, respectively), according to the position of a filled green circle (preparatory cue) that appeared on the left or right side of the screen. Subjects had to wait until an imperative signal (Go!) before they could initiate their response. FDI = first dorsal interosseous. (B) Time course of events: a fixation cross (displayed for 400 ms) indicated the beginning of the trial and was followed, after a blank delay of 500 ms, by a preparatory cue (displayed for 400 ms), indicating the side of the forthcoming response. After another blank delay (500–700 ms), an imperative signal gave the order to trigger the appropriate response as quickly as possible. Hence subjects had to withhold their response between the preparatory cue and the imperative signal onset, a period referred to as the delay period. The imperative signal disappeared once a response was provided or after a maximum duration of 2 s. A feedback score was then displayed for 750 ms reflecting the performance (inversely proportional to the RT) on the preceding trial. The trial ended with a blank screen that lasted for a random duration ranging from 2000 to 2500 ms. (C) Three experimental blocks: transcranial magnetic stimulation (TMS) was either applied using a Single-Coil method with pulses delivered to the left primary motor cortex (left M1 = LM1, Single-Coil_LM1 block: MEPs elicited in the right FDI, MEP_Right) or to the right M1 (Single-Coil_RM1 block: MEPs elicited in the left FDI, MEP_Left) or using a Double-Coil method (Double-Coil block [1 ms delay between the two pulses]: MEP_Right and MEP_Left elicited concurrently). The task remained the same across the three blocks. (D) TMS timings: Single- or Double-Coil TMS was delivered at one of two possible timings, either at the onset of the fixation cross (at TMS_BASELINE) or during the delay period (at TMS_DELAY), 850 ms after the preparatory cue onset (falling 50–250 before the imperative signal), eliciting MEPs in the left (MEP_Left) and/or right (MEP_Right) FDI. The current example displays a trial in which TMS pulses were delivered using a Double-Coil procedure, thus eliciting MEP_Left and MEP_Right, concurrently (1 ms delay, see “Materials and Methods” Section); the pulse order was counterbalanced between subjects (TMS_LRM1 group [LM1-RM1 order, n = 12] and TMS_RLM1 group [RM1-LM1 order, n = 12], not depicted on figure).