You See What You Smell: Preferential Processing of Chemosensory Satiety Cues and Its Impact on Body Shape Perception

Abstract

The current study examines neural responses to satiety- and fasting-related volatiles and their effect on the processing of body shapes. Axillary sweat was sampled with cotton pads from 10 individuals after 12 h of fasting, and after having consumed a standard breakfast. Pure cotton pads served as the control. The chemosensory stimuli were presented to 20 participants (via a constant-flow olfactometer) exclusively, and additionally as context to images of overweight and underweight avatars. EEG was recorded (61 electrodes), and chemosensory (CSERPs; P1, N1, P2, P3) and visual event-related potentials (VERPs; N1, P2, P3a, P3b) were analyzed. The amplitudes of all positive CSERP components differed more strongly from cotton in response to chemosensory satiety cues as compared to fasting cues (P1: p = 0.023, P2: p = 0.083, P3: p = 0.031), paralleled by activity within the middle frontal and temporal gyrus. Overweight compared to underweight body shapes tended to elicit larger VERP P2 amplitudes (p = 0.068), and chemosensory satiety cues amplified the VERP amplitudes in response to any body shape (P2, P3a, P3b; all p_s ≤ 0.017) as compared to the cotton control. The results indicate that chemosensory satiety cues transmit complex social information, overriding the processing of analogous visual input.

Keywords: BMI; body odors; chemosensory communication; chemosensory cues; diet; event-related potentials; fasting; metabolic state; olfaction; satiety.

Figure A1

Examples of underweight (A,C; BMI = 10.5 kg/m²) and overweight (B,D; BMI = 39.5 kg/m²) female (A,B) and male (C,D) avatars [25].

Figure 1

Sweat donors’ mean (±SEM) blood glucose levels (A) and hunger ratings (B).

Figure 2

Schematic overview of the time sequence of one trial during an EEG recording.

Figure 3

(A) Grand average of the chemosensory event-related potentials (CSERPs) in response to satiety sweat (solid black line), fasting sweat (dashed black line), and cotton (solid grey line). (B) Grand average of the difference chemosensory event-related potentials (Delta CSERPs) in response to satiety sweat in reference to cotton (solid line), and fasting sweat in reference to cotton (dashed line). Timepoint 0 refers to the activation of the switching valves.

Figure 4

Low-resolution electromagnetic tomography analysis (LORETA) maps depicting the location of the maximum current density (in μA/mm²) upon the presentation of satiety sweat, fasting sweat, and cotton at the time of the individual mean P1 (satiety sweat = 358 ms, fasting sweat = 328 ms, cotton = 352 ms), N1 (satiety sweat = 480 ms, fasting sweat = 444 ms, cotton = 460 ms), P2 (satiety sweat = 654 ms, fasting sweat = 654 ms, cotton = 684 ms), and P3 latencies (satiety sweat = 892 ms, fasting sweat = 874 ms, cotton = 896 ms).

Figure 5

Grand average of the visual event-related potentials (VERPs) in response to overweight (black line) and underweight avatars (grey line) in the context of satiety sweat (left column), fasting sweat (middle column), and cotton (right column) at Fz (upper row), Cz (middle row), and Pz (lower row). Timepoint 0 refers to the onset of the avatars’ presentation.

Figure 6

(A) Grand average of the visual event-related potentials (VERPs) in response to overweight (black line) and underweight avatars (grey line) across all chemosensory context stimuli. (B) Grand average of the visual event-related potentials (VERPs) in response to all avatar shapes in the context of satiety sweat (solid black line), fasting sweat (dashed black line), and cotton (solid grey line). Timepoint 0 refers to the onset of the avatars’ presentation.