, 2009 for details). During laser positioning
white noise was played to disguise any potential auditory cues from the servo-motors controlling the laser beam. An audio cue was then played instructing the participant to judge either the intensity or location of the subsequent stimulus, which consisted in a laser pulse of either high or medium intensity. A single TMS pulse was delivered 120 msec after the laser stimulus. This latency was chosen on the basis of the results of previous EEG studies to coincide with the selleck compound onset of the N1 sensory component of the LEP, which is largely generated in the S1 (Valentini et al., 2012). Each trial lasted a minimum of 5 sec to limit any TMS carry over effects and to ensure that the laser did not stimulate each location more than once a minute (see above). A break of at least 1 min was given at the end of each block in order to change the laser stimulation sequence, reposition Bax apoptosis the TMS coil
and measure the participants’ skin temperature. Participants’ baseline skin temperature was kept at approximately 30 °C [mean ± standard deviation (SD), 30.2 ± .2]. The experimental session consisted of six blocks (one block per each TMS stimulation site repeated twice) of 48 trials, resulting in 288 trials in total. The order of TMS conditions was counterbalanced across participants, and reversed using an ABCCBA design to minimize time-dependent effects. One participant spontaneously
observed that she had not understood the definitions of the ‘proximal’ and ‘distal’ response categories used in the location judgement task, and was replaced. One further participant showed an outlying pattern of very low accuracy (3.2 SDs below the group mean in the vertex control condition, and significantly below chance) on the final block of the experiment (intensity judgement, vertex control). This participant was excluded, but not replaced, leaving a sample of 17 participants. Preliminary analyses showed that location Aspartate and intensity judgement tasks had been successfully matched for difficulty (localisation mean % accuracy = 70.3%, SD = 8.5; intensity judgement mean % accuracy = 72.3%, SD = 6.2). Next, we investigated whether areas S1 and S2 contributed to pain perception by simultaneously analysing the accuracy of intensity and location judgements, using one-way multivariate analyses of variance (MANOVA) with a single factor of TMS condition having three levels (S1, S2, and vertex). The MANOVA revealed a multivariate effect of TMS on pain perception which achieved the boundary of statistical significance [Wilks' Lambda = .742, approximated by F(4, 62) = 2.50, p = .05, Δη2 = .139].