Background & Aims: In human beings, as in most vertebrates, the release of the intestinal peptide cholecystokinin (CCK) by ingested food plays a major role both in digestion and the regulation of further food intake, but the changes in brain function and their underlying activation mechanisms remain unknown. Our aim was to explore, using a novel physiologic magnetic resonance imaging approach, the temporospatial brain activation matrix, in response to ingestion of a lipid meal and, by use of a CCK-1 receptor antagonist, to define the role of CCK in this activation. Methods: We studied, in 19 healthy subjects, the brain activation responses to ingested lipid (dodecanoic acid) or saline (control) with magnetic resonance imaging. Gallbladder volume, plasma CCK levels, and subjective hunger and fullness scores were also recorded. The experiment was then repeated, with and without prior administration of the CCK-1 receptor antagonist dexloxiglumide (600 mg orally) with a controlled, randomized order, latin-square design. Results: Ingested lipid activated bilaterally a matrix of brain areas, particularly the brain stem, pons, hypothalamus, and also cerebellum and motor cortical areas. These activations were abolished by dexloxiglumide, indicating a CCK-mediated pathway, independent of any nutrient-associated awareness cues. Conclusion: The identification of these activations now defines the lipid-activated brain matrix and provides a means by which the gut-derived homeostatic mechanisms of food regulation can be distinguished from secondary sensory and hedonic cues, thereby providing a new approach to exploring aberrant human gastrointestinal responses and eating behavior. © 2010 AGA Institute.