Using functional MRI, we examined how regional brain activity varies with nutritional state when viewing food pictures of different caloric density and appeal.
Eighteen non-obese healthy volunteers (BMI 22.2±0.5 kg/m2, age range 1936 years, 8 male) were studied on 2 separate mornings after an overnight fast (mean±S.E.M. 15.5±0.3 h) or when fed (1.2±0.1 h after breakfast, food intake 45±4% of estimated REE). Appetite was scored using visual analogue scales.
fMRI was performed while viewing pictures of: i) high-calorie and ii) low-calorie foods, and iii) non-food related household objects using a 3T MR scanner (TR 3 s, 44×3.25 mm slices, 2.5 mm voxels). Subjects rated how appealing they found each picture while being scanned. SPM5 was used for image pre-processing and GLM analysis using a priori regions of interest (ventral striatum, insula and amygdala) with a statistical threshold of P<0.005. Average activation in each ROI per subject was determined using the MarsBar tool.
Hunger and pleasantness-to-eat ratings were greater in the fasted versus fed state (P<0.001). Both high- and low-calorie food pictures were more appealing when fasted than when fed (P<0.001). High-calorie pictures were more appealing than object and low-calorie pictures when fasted (P<0.001 and 0.01), but not when fed (P=0.7 and 0.2).
There was activation of the ventral striatum, insula and amygdala when viewing high-calorie versus object, or high- versus low-calorie, pictures when fasted, but minimal if any when fed. The greater average activation of these brain regions when fasted versus fed (P<0.05) reflected the difference in rating for the pictures (P<0.001).
Thus increased hunger and desire for food, particularly high-calorie foods, when fasted (versus fed) is associated with increased activation in brain regions involved in reward, craving and emotion (ventral striatum, insula and amygdala). Changes in gut hormones may be one mechanism by which such brain activity is modulated to alter human appetite.