Activation in brain energy regulation and reward centers by food cues varies with choice of visual stimulus

Objective: To develop a non-invasive method of studying brain mechanisms involved in energy homeostasis and appetite regulation in humans by using visual food cues that are relevant to individuals attempting weight loss. Design: Functional magnetic resonance imaging (fMRI) was used to compare brain activation in regions of interest between groups of food photographs. Participants: Ten healthy, non-obese women who were not dieting for weight loss. Measurements: Independent raters viewed food photographs and evaluated whether the foods depicted should be eaten by individuals attempting a calorically-restricted diet. Based on their responses, we categorized photographs into 'non-fattening' and 'fattening' food groups, the latter characterized by high-caloric content and usually also high-fat or high-sugar content. Blood oxygen level-dependent (BOLD) response was measured by fMRI while participants viewed photographs of 'fattening' food, 'non-fattening' food, and non-food objects. Results: Viewing photographs of fattening food compared with non-food objects resulted in significantly greater activation in the brainstem; hypothalamus; left amygdala; left dorsolateral prefrontal cortex; left orbitofrontal cortex; right insular cortex; bilateral striatum, including the nucleus accumbens, caudate nucleus, and putamen; bilateral thalamus; and occipital lobe. By comparison, only the occipital region had greater activation by non-fattening food than by object photographs. Combining responses to all food types resulted in attenuation of activation in the brainstem, hypothalamus, and striatum. Conclusion: These findings suggest that, in non-obese women, neural circuits engaged in energy homeostasis and reward processing are selectively attuned to representations of high-calorie foods that are perceived as fattening. Studies to investigate hormonal action or manipulation of energy balance may benefit from fMRI protocols that contrast energy-rich food stimuli with non-food or low-calorie food stimuli.