The main disadvantage for brain imaging studies on experimental itch is the wide variability of the itch sensation induced by skin prick or iontophoresis. In this study microdialysis was used to evoke several periods of itch during one fMRI session.

10 healthy subjects participated on two group studies that analysed the correlation between the BOLD signal and continuous rating of itch or pain, repectively. BrainVoyager was used for analysis. Histamine and codeine were applied through microdialysis fibers into the skin of the left forearm to provoke itch. The sensation was stopped by lidocaine through the same fibre. This procedure was repeated four times through four different microdialysis fibres, including one placebo control. The subjects were not allowed to scratch. In the second fMRI study, thermal pain was applied to the right forearm.

During itch and pain, activation clusters were found in brain areas which have been described as to be part of the so called pain matrix. These included prefrontal areas, SMA, premotor cortex, anterior insula, anterior MCC, S1, S2, thalamus and cerebellum. However, only during itch, negative BOLD signals were found in the subgenual ACC and the amygdala. We interpret this as a general limbic deactivation during anticipation of pain as it was suggested earlier by Petrovic et al (2004, J.Cogn Neurosci.). This anticipation is induced by the possible noxious stimulus of scratching, which would normally follow an itching sensation.