The temporal response of the brain after eating revealed by functional MRI

After eating, the human brain senses a biochemical change and then signals satiation, but precisely when this occurs is unknown. Even for well-established physiological systems like glucose-insulin regulation, the timing of interaction between hormonal processes and neural events is inferred mostly from blood sampling(1-6). Recently, neuroimaging studies have provided in vivo information about the neuroanatomical correlates of the regulation of energy intake(7-10). Temporal orchestration of such systems, however, is crucial to the integration of neuronal and hormonal signals that control eating behaviour(11). The challenge of this functional magnetic resonance imaging study is to map not only where but also when the brain will respond after food ingestion. Here we use a temporal clustering analysis technique to demonstrate that eating-related neural activity peaks at two different times with distinct localization. Importantly, the differentiated responses are interacting with an internal signal, the plasma insulin. These results support the concept of temporal parcellation of brain activity(12), which reflects the different natures of stimuli and responses. Moreover, this study provides a neuroimaging basis for detecting dynamic processes without prior knowledge of their timing, such as the acute effects of medication and nutrition in the brain.