Figure 1.

fMRI stimulus presentation and session design. A, The taste run was 6 m 32 s long and consisted of the uncued delivery of 2 different types of stimuli: 1, a 4 s delivery of either chocolate or strawberry milkshake, followed by a 6–13 s rest period, a 4 s tasteless rinse, and another 6–13 s rest period; or 2, a 4 s delivery of tasteless solution, followed by a 6–13 s rest period. The subjects were instructed to swallow and exhale through their nose after receiving each liquid. There were 10 repetitions of each of the two events of interest (milkshake and tasteless), resulting in 20 presentations per run. B, The odor run was 5 m 54 s long and subjects were instructed to breathe in through their nose after receiving the prerecorded verbal instructions “3, 2, 1, sniff” through headphones. Odor or odorless delivery occurred immediately after the auditory cue so that delivery was time locked to sniff onset. Olfactory stimulation lasted for 3 s, followed by a 9–19 s rest period before the next trial. There were six repetitions of each of the three events of interest (food odor, nonfood odor, odorless), resulting in 18 presentations per run. C, During fMRI scan sessions, subjects made internal state ratings at each time point (1–9). At time point 1, a Teflon catheter was inserted into an antecubital vein for blood sampling. Subsequent asterisks (*) indicate IV blood draws that occurred concomitant to internal state ratings. After time point 3, subjects ate either a fixed-portion meal (at the sated scan, consisting of 1 sandwich and 1 serving of apple slices for women, 1.5 sandwiches and 1 serving of apple slices for men) or nothing (at the hungry scan). T (time) = 0 indicates time of meal onset. Subjects made postmanipulation internal state ratings at time point 4 and then were taken to the scanner, outfitted with the stimulus delivery devices, and inserted into the bore. Internal state ratings and further blood samples were collected at T = 30, 60, and 90 min from meal onset. Perceptual ratings of the stimuli were collected as in the training session inside the scanner before and after scanning. After subjects were removed from the scanner, they were taken to a behavioral testing room, where they were presented with both flavors of milkshake followed by the tub of cheese pasta and instructed to eat ad libitum from both. Milkshake and pasta intake were recorded without the subjects' knowledge by weighing before and after consumption.