Attention, inhibition and food: a neuroscientific investigation of eating disorders and obesity

Eating disorders (ED, i.e. anorexia nervosa, bulimia and binge eating) and obesity have been linked to attentional biases for and altered inhibition of responses to food stimuli. However, these two groups of patients have rarely been investigated together in the same studies. The goal of this study is to fill this gap in the literature by investigating subliminal visual processing of food stimuli and response inhibition in both ED patients and overweight/obese participants. Seventy-four participants (25 ED patients, 24 overweight and obese, and 25 healthy controls) were enrolled in this study. Subliminal processing of food and non-food stimuli was measured with a breaking continuous flash suppression (bCFS) task, while impulsivity was measured with a Go/No-Go task. Among participants with ED symptoms, higher BMI predicted faster awareness in the bCFS task, especially of food images compared to non-food images, and shorter RTs to food Go cues in the Go/No-Go task. Altered subliminal processing of and heightened attention for food stimuli was found in patients who suffered from both dysfunctional eating habits and obesity. These results demonstrate the need to also include obese participants in future studies on processing biases in ED patients, to better understand attentional biases for food.

Obesity has been linked to low performance in the attention and impulsivity domains. Obese individuals, compared with healthy-weight participants, exhibit increased attentional bias to food cues. Notably, the prefrontal cortex plays a central role in cognitive control over food choices and is less active in obese individuals. By using direct current stimulation (tDCS), the study investigated the role of the right dorsolateral prefrontal cortex (dlPCF) in subliminal visual processing of, and in the inhibition of responses to food pictures, in individuals with healthy vs. obese body mass index (BMI). Obese individuals were expected to show a subliminal food bias and reduced inhibition. Moreover, modulation of the dlPFC by tDCS was expected to impact on this pattern. In a within-subject design, fifty-three participants with a BMI ranging from 17 to 34 received in separate sessions, anodal, cathodal, or sham tDCS over the right dlPCF. Subliminal processing was measured with a breaking Continuous Flash Suppression task (bCFS), and inhibition was assessed with a Go/No-Go task. In both tasks, food-related and unrelated pictures were presented. Data were analyzed using Linear Mixed Models (LMMs). In the bCFS task, a higher BMI led to longer detection times for both food and nonfood pictures [p = 0.02]. In the Go/No-Go task, higher BMI led to slower responses in food Go trials [p = 0.02]. Anodal stimulation resulted in shorter detection times in the bCFS task in all participants [p < 0.001], but especially in those with higher BMI [p = 0.01]. Cathodal stimulation did not interact with participants’ BMI in neither the bCFS nor the Go/No-go tasks. The results indicates that an attentional bias for food is not present at a subliminal level of processing, and that it might be present only at a late stage of attentive processing. The study also revealed that obesity might be associated with a generally increased threshold of perceptual awareness. This association has never been reported before. Moreover, these findings indicate that anodal stimulation improves attentional performance of all participants, especially in those with higher BMIs, and particularly at a subliminal level. This is in accordance with the evidence of reduced dlPFC activity in obesity and, more generally, in eating disorders.

Food is a salient stimulus and as such it is preferentially attended. From early stages of stimulus processing, obesity and eating disorders influence attention and inhibition towards food. Subliminal processing of food is also altered in individuals with a high BMI and ED symptoms, and a higher BMI has been linked to a higher threshold for visual awareness. In this study we explore the neural correlates of suppression and inhibition of food and non-food stimuli. Fifty-three participants completed a breaking Continuous Flash Suppression (bCFS) task and a Go/No-Go task with food and non-food stimuli. We collected whole-brain structural magnetic resonance images and used voxel-based morphometry to measure grey matter (GM) density. We find that higher GM density in visual (left calcarine and occipital cortex) and reward areas (bilateral caudate nuclei) is associated with longer suppression times in the bCFS task, while higher GM density in control areas is associated to shorter suppression times in the bCFS task (left frontal gyrus) and faster reaction times in the Go/No-Go task (left frontal pole). Higher hypothalamic and lower postcentral cortex GM density are associated with higher Body Mass Index and more severe self-reported eating disorder symptoms. Moreover, some areas in the reward and control circuit (left orbitofrontal cortex, left insula, right dorsolateral prefrontal cortex, bilateral temporal areas) are differentially correlated to suppression times in participants with a high BMI. In conclusion, the reward and control circuits are involved in subliminal processing, and altered suppression times are associated with morphological alterations of these regions.