Neuronal and Behavioral Effects of Implicit Priming in Obese Individuals

The overall goals of this project are to determine the impact of an implicit priming intervention, designed to alter food perceptions, on both brain responses to food and on food intake behaviors in overweight/obese individuals. The investigators hypothesized that this bottom-up sensory-level conditioning approach would effectively result in reduced preference for high-calorie foods.

One factor that may contribute to susceptibility to obesity is a high responsivity to high-calorie foods in terms of cognitive factors such as emotional associations, reward value or reinforcing properties of food. Many of these processes involve learned associations thought to develop via classical conditioning through repeated pairings with external stimuli, which can influence food preferences and intake. As such, improving our understanding of the neuronal mechanisms underlying these processes and attempting to modify them may be a useful strategy to promote weight loss and maintenance. Therefore, the proposed study aims to investigate the effects of altering food perception on neuronal responses and food intake behaviors by using implicit priming, in which positively or negatively valenced images are presented immediately prior to food images, but are not consciously perceived. The project goals are to determine the impact of the implicit priming intervention on both brain responses to food cues and on food intake behaviors in overweight/obese individuals. Food image ratings were assessed before and after either (a) an active implicit priming intervention or (b) a control intervention. One group of participants (n = 47; "MRI sample") completed the intervention during an fMRI scan and completed a visual food cues task both before and after the intervention (during fMRI), to assess intervention-related change in neuronal responses to food cues. In this group, food intake measures were also taken following fMRI. In a separate group of participants (n = 45; "Behavioral-only sample"), the primary outcome measure was the change in food image ratings from pre- to post-intervention; fMRI and measures of food intake were not assessed in this group.

The "MRI sample" and "Behavioral-only sample" involve separate participants who complete the same intervention (assigned to either active or control groups), but the "MRI sample" also completed MRI outcomes and a food intake outcome that the "Behavioral-only sample" did not.

Participants will complete active implicit priming, in which food images are implicitly primed (i.e., below conscious awareness) with images of positive or negative affect. In addition to measures of food image ratings, this group completed a visual food cues scan during fMRI to assess change in neuronal response to food cues. They also completed a measure of food intake post-intervention.

Participants will complete a control implicit priming intervention, which matches the active intervention, but with neutral stimuli as primes. In addition to measures of food image ratings, this group completed a visual food cues scan during fMRI to assess change in neuronal response to food cues. They also completed a measure of food intake post-intervention.

Participants will complete active implicit priming, in which food images are implicitly primed (i.e., below conscious awareness) with images of positive or negative affect.

Participants will complete a control implicit priming intervention, which matches the active intervention, but with neutral stimuli as primes.

A 10-minute implicit priming intervention, associating food images with images of positive or negative valence.

Food image ratings (high-calorie foods) change from baseline, measured within 10 minutes post-intervention. Food images are rated on "desire to eat" by visual analogue scale (0-100; higher scores mean greater desire to eat). Negative values indicate reduced scores post-intervention compared to baseline, with greater numbers indicating greater reduction.

Neuronal response while viewing visual food cues will be measured using functional magnetic resonance imaging (fMRI). Primary outcome was insula response change from baseline, as measured within 20 minutes after the intervention. A bilateral region of interest (ROI) for the insula was defined anatomically, with mean difference from baseline to post-intervention (% BOLD signal change) calculated across all voxels for that ROI. A positive number indicates a reduced response (with higher numbers indicating greater change) and a negative number indicates an increased response.

Inclusion Criteria: Overweight/obese adults Healthy weight adults Exclusion Criteria: Vegetarian, vegan, or having other wide-ranging food restrictions Currently dieting MRI exclusion criteria, if in MRI sample (e.g., claustrophobia, metal in the body)

Legget KT, Cornier MA, Erpelding C, Lawful BP, Bear JJ, Kronberg E, Tregellas JR. An implicit priming intervention alters brain and behavioral responses to high-calorie foods: a randomized controlled study. Am J Clin Nutr. 2022 Apr 1;115(4):1194-1204. doi: 10.1093/ajcn/nqac009.

Legget KT, Cornier MA, Rojas DC, Lawful B, Tregellas JR. Harnessing the power of disgust: a randomized trial to reduce high-calorie food appeal through implicit priming. Am J Clin Nutr. 2015 Aug;102(2):249-55. doi: 10.3945/ajcn.115.106955. Epub 2015 Jun 24.