Odorant delivery in the MRI

Odorants were delivered using a computer-controlled air-dilution olfactometer that was optimized for naturalistic delivery in the MRI (71). The olfactometer emitted a constant flow of olfactometer air (1.5 l/min) that carried embedded 10-s pulses of odorant (HEX or control). Nasal airflow was constantly precisely monitored using a nasal cannula linked to spirometer (ML141, ADInstruments) and instrumentation amplifier (Power-Lab 16SP, ADInstruments). Because HEX at this concentration and mineral oil have no perceivable odor, we validated precise olfactometer timing with a photoionization detector (RAE Systems, model ppbRAE 3000). In each experiment, there were a total of four runs: two with HEX (CAS #629-80-1, 0.083 M, supplied by TCI and Cayman) and two with control (mineral oil alone, CAS #8042-47-5, Sigma-Aldrich). The order of conditions was counterbalanced, and the given condition was unknown to participants or experimenters. Only 2 of 58 participants reported that they smelled any odor during the experiment. Odor ratings were completed inside the scanner after completion of the FC-PSAP. At the end of the experiment, participants completed an exit questionnaire probing their thoughts, strategies, and attitudes toward their game partners, a general demographics questionnaire, AGQ, AQ, and STAI.