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Paying attention to food: investigating the mechanisms underlying individual differences in the attention grabbing properties of food

Final Report Summary - FOOD ATTENTION (Paying attention to food: investigating the mechanisms underlying individual differences in the attention grabbing properties of food)

The prevalence of obesity has increased worldwide to epidemic proportions. Obesity results from a chronic deregulation of energy balance, with energy intake exceeding energy expenditure. Individual susceptibility to disturbance of energy balance is determined by interactions between genetic, behavioural, and environmental factors. One potentially important behavioural factor is responsiveness to seeing food, as obese people and dieters have been shown to be hypersensitive to the presence of food and to attend strongly to food when compared to lean subjects. Enhanced attention to food likely promotes intake via the elicitation of food cravings, which in turn might lead to excessive energy intake. The ubiquitous presence of food images in our environment may thus undermine the efforts of dieters and overweight individuals to reduce food intake and in turn to lose weight, which would have major health benefits. However little is known about the mechanisms underlying individual differences in attention to food. Therefore, the objective of our current project was to provide new information that will help explain why some people pay a lot of attention to food and are therefore susceptible to overeating. This project brought together several scientific disciplines (genetics, psychology, and neuroscience) with the aim of connecting genetic factors to behavioural factors predisposing individuals to obesity.

First, we wanted to test the idea that food attention can be influenced by top down regulation of attention via working memory. The School of Psychology, University Birmingham has a well-developed paradigm for assessing the interaction between memory and attention. We used this paradigm to show in 23 young and lean participants (15 females and 8 males, age 23 years, BMI 23 kg/m2) that food can exert special top-down control of attention from working memory. When a food stimulus is held in working memory, there is a greater tendency for attention to be drawn to food stimuli. The guidance of attention by working memory was found to be stronger for food than non-food items. This suggests a mechanism whereby individuals who think about food a lot - for example dieters and the obese - show particular attention to food cues in the environment. Holding food related information in working memory guides attention to similar items. This data was been published in 2012 in the journal Appetite.

Second, we wanted to establish why food is such a potent stimulus in guiding attention, when kept in working memory. Could it be that food cues are more salient because of their rewarding properties, resulting in individual differences in attention to food cues? We addressed these questions by examining the neural correlates of the effects of holding food vs. non-food information in working memory on attention using both EEG and fMRI brain imaging techniques. This provided us with the first-ever analysis of the brain mechanisms that underlie the capture of attention by food items, giving us novel insights into how the neural circuits of attention are affected by holding food in working memory. While EEG measurements were taken, 16 young and lean participants (8 females and 8 males, age 23 years, BMI 25 kg/m2) were presented with a cue (food or non-food item) to either attend to or hold in working memory. Subsequently, they had to search for a target, while the target and distractor were each flanked by a picture of a food or non-food item. Behavioural data showed that performance was more strongly affected by food cues, especially when it was held in memory compared to when it was merely attended to. An electrophysiological measure of attention and memory processing of motivational salient stimuli (P3 component) was affected by food flanking the target. electrophysiological measures of working memory, the late positive potential (LPP) and the sustained posterior contralateral negativity (SPCN) components were affected by the match between food cues in working memory and the cue being next to the target in the search task, compared to when the food cue was merely attended to. Overall, we again observed that working memory is particularly effective in guiding attentional deployment of food stimuli. The new evidence from the EEG study suggests that the attentional bias towards food is regulated by enhanced representation of food cues in working memory based on rewarding properties and that food items are more strongly represented in working memory compared to non-food items. These data have been written up and will be sent out for publication.

In a subsequent study in which we used fMRI, 15 young, lean and female participants (age 20 years, BMI 21 kg/m2) were presented with a cue (food or non-food item) to hold in working memory. Subsequently, they had to search for a target, while the target and distractor were each flanked by a picture of a food or non-food item. Behavioural data showed that performance was more strongly affected by food cues, especially when it was held in memory compared to non-food items, similar to the EEG study. In our preliminary analysis, we observed increased activation in the right Caudate and right Hippocampus when food reappeared next to the target. These data suggest (in concordance to the electrophysiological findings), that the attentional bias towards food is regulated by enhanced representation of food cues in working memory based on rewarding properties. This data is currently being analysed further, will be written up and sent out for publication.

Third, we wanted to establish the role of genetic factors in why food is such a potent stimulus in guiding attention, when kept in working memory. Genes and genetic predisposition contributes to obesity development, and up until now the contribution of genetic variation to food attention has not been investigated. In our behavioural study, 69 participants with a wide range in BMI from 15 - 37 kg/m2 were presented with a cue (food or non-food item) to either attend to or hold in working memory. From all participants several metabolic, behavioural, and genetic factors were determined, including mood, appetitive feelings, reward sensitivity, eating behaviour, and several Single Nucleotide Polymorphisms. The preliminary evidence suggests that variation in attention to food was explained by behavioural and genetic factors. Participants with a polymorphism associated with variation in responses in the brain reward system (the DRD2TaqIA1 allele) showed heightened attention to food. These data suggest that individuals with genetically predisposed altered reward processing are vulnerable to the attention grabbing properties of food. These data is currently being analysed further, will be written up and sent out for publication.

Thus, the results of this project provide us with better understanding of why food is such a potent stimulus in guiding attention, especially when kept in working memory. One implication of the findings is that treatment for obesity should take into account individual differences in processing of food-related stimuli because for some people attention to food could be a factor driving overeating and weight gain. Future studies are necessary to elucidate possible treatment options that exploit the use of working memory training.