Fig. 1.

Experimental flow chart. During each experimental session, 30 phasic nicotine stimuli were applied to the nasal mucosa using an olfactometer (stimulus duration of 1 s; interstimulus interval of 1.5 min). Within one session, only one of the two nicotine concentrations was used (99 ng/mL or 134 ng/mL). In the second half of the session (i.e., after 22.5 min), the continuous background air flow was switched from clean air to one of the four menthol conditions (no menthol: placebo control; menthol-low: 0.8 μg/mL; menthol-medium: 1.5 μg/mL; menthol-high: 3.4 μg/mL). Each of the four menthol conditions was combined with one of the two nicotine concentrations. All these combinations resulted in eight experimental sessions on eight different days. Acoustic rhinometry was performed in each participant before and after each session. On the VAS, participants rated the stinging and burning pain elicited by nicotine as well as odor, cooling and pain sensations caused by tonic background menthol stimulation