Figure 1

Biphasic stimulus model using 32°C stimulation to decrease and 25°C stimulation to increase histamine-induced itch. The red/blue columns represent the mean itch intensity (VAS range, 0-100) of 9 healthy volunteers obtained every 4 seconds during the 20 seconds of the 32°C stimulation (red columns were numbered 1-5) and during the 20 seconds of the 25°C stimulation period (blue columns were numbered 6-10). Two sessions, each with 14 consecutive cycles of 32°C followed by 25°C stimulation, were applied. The yellow line represents the scratch threshold (33% itch intensity). Asterisks indicate significant differences between rating intervals. **P < 0.01, ***P < 0.001. From Pfab et al[13].