Three right-handed participants (one male, mean age ± SD: 26.7 ± 6.4 years) who took part in the previous experimental UK-371804 concentration session volunteered for this second experiment. Procedures were approved by the University College London ethics committee. At the beginning of the testing session verbal and written instructions were given to participants. Testing was performed Pre-CVS and Post-CVS, as in Experiment

1. The same CVS procedure adopted in the Experiment 1 was used, irrigating the left auditory canal for 30 sec with cold iced water. The participant’s head was positioned 30° backward from the horizontal plane and 30° towards the right. The somatosensory task started only when participant had reported that vertigo had ceased. Thresholds for the painful pinprick sensation elicited by selective activation of the nociceptive Aδ pathway were measured using Nd:YAP laser stimulation (Iannetti et al., 2006). Laser stimuli were p38 MAPK Kinase pathway delivered in blindfolded participants without any tactile contact immediately before (Pre-CVS condition) and after CVS (Post-CVS condition) (Fig. 3B and C). Each trial consists of a method of limits search to identify the threshold for the painful pinprick sensation characteristic

of Aδ firing. The general procedure was as for the first experiment. A laser pulse of 4 msec of duration was directed to the index fingertip of the left hand. It was transmitted via an optic fibre and delivered with a spot diameter of 8 mm (50 mm2) at the target site. After each stimulus, to avoid nociceptor fatigue and sensitization, the spot location was shifted to another site of stimulation (Fig. 2B), in randomized order. Laser intensity was initially set at 1.75 J, and increased in steps of .25 J

until the subject first felt the O-methylated flavonoid ‘pinprick’ sensation related to the activation of Aδ nociceptors (Bromm and Treede, 1984). Data from five different thresholding runs were collected and then averaged. Because variations in baseline skin temperature could influence the temperature achieved by laser stimulation (Baumgartner et al., 2005), an infrared thermometer was used to monitor whether baseline skin temperatures were affected by CVS stimulation. Skin temperature was measured before each trial. CVS significantly increased nociceptive thresholds on average by .33 J [F(1,2) = 30.769, p = .031], even in the absence of touch ( Fig. 3D). Including baseline skin temperature as a covariate showed that CVS effect remained significant, and the estimated pain threshold increase remained unchanged at .33 J, even after correction for baseline skin temperature [F(1,2) = 4.332, p = .047]. Further, baseline temperature itself was not significantly related to nociception (p > .05).