Design: Subjects will complete a unique session. They will perform a serial-reaction-time task. The subjects will be instructed to push a button on a 4-button pad in response to a visual GO signal (which can appear at 4 different positions) using the appropriate digit and the appropriate button. There will be 9 blocks of 120 trials each. In the test group, in blocks 1, 4 and 7 the Go signal appears in a random order; in blocks 2-3, 5-6 and 8-9 the same 12-trial sequence is repeated 10 times. In the control group Go signals will appear in a random order in all blocks. Subjects won't be informed about the sequence but will be asked to notify anything they noticed about the task. If they do notice and report about a sequence they will be considered as having explicit knowledge. Between each block subjects will receive transcranial magnetic stimulations to assess ICI. ICI will be assessed on subjects at rest.