All participants tolerated the TMS well and there were no adverse effects. To familiarise participants with the experimental procedure and to locate the various brain locations, as well as the appropriate laser intensities and locations, a training session was conducted on a separate day, but within 48 h of the experimental session. Before the training task began, participants were shown a figure of a hand with the hand dorsum sites that would be stimulated during the training and experimental sessions, to ensure that they understood the meanings of the labels ‘proximal’ and ‘distal’. During this training session, participants completed 20 trials, 10 of the

intensity find more judgement (medium/high) and 10 of the APO866 location judgement (proximal/distal), after which feedback was given. If accuracy was below 60%, an additional training block of 10 trials was performed. Once this criterion was reached, the training session was terminated. During the experimental session, participants’ vertex,

S1 and S2 were marked with a pen, on the basis of the co-ordinates determined in the training session. The location of S1 was reconfirmed, by delivering one pulse at M1 and one pulse at S1, to ensure that the former produced a detectable motor twitch but that the latter did not. Participants were then seated with their left hand occluded behind a screen. They used a computer mouse held in the right hand to report location/intensity judgements on each trial. At the beginning of the experimental session an example of one medium, one high, one proximal and one distal stimulus were applied to the hand dorsum to remind participants of the stimuli to detect. Participants were instructed to make an un-speeded response by clicking on one of two boxes labelled either ‘medium’ ‘high’ that appeared on screen for the intensity trials, or ‘proximal’ ‘distal’ that appeared for location trials (see Fig. 1 for an example of the sequence of events in an experimental trial). Participants Sodium butyrate were told that accuracy was important but response time was not. Six sequences of 12 randomised trials, balanced between intensity and location

judgements, pulses on the proximal or distal line, as well as laser pulses of medium and high intensity, were created. Intensity and location trials were used in the same blocks to limit any effects of learning, comparison between trials, and expectation. There were never more than three stimuli in succession on either the proximal or distal line, or of medium or high intensity. Each sequence was repeated four times, resulting in 48 trials per block. This method was used to ensure that at least 1 min elapsed between stimulations of the same location, in order to minimise increases of baseline temperature and to limit nociceptor fatigue or sensitization (Iannetti et al., 2004). Block order was randomized among participants. However, one participant received the same sequence for two blocks due to experimenter error.