Localising awareness of action with transcranial magnetic stimulation

Seven subjects reacted to an auditory stimulus by pressing a response key and judged their reaction time (RT) by reporting the position of a rotating clock-hand at which they pressed the key. Transcranial magnetic stimulation (TMS) was delivered either over primary motor cortex (MI) or more anteriorly (with the centre of the coil over FCz) 75 ms before each subject's median reaction time. TMS over MI produced substantial delays in actual RT, but much smaller delays in judged RT. TMS over FCz produced smaller delays in actual RT and relatively larger delays in judged RT. We conclude that awareness of responses is generated, at least in part, between premotor areas affected by stimulation over FCz and the primary motor cortex.