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Imaging study sheds light on brain’s response to food (6-26-00)

There’s more to feeling full than having a knot in one’s stomach. In fact, specific parts of the brain are activated so that you feel ready to push away from the table, say researchers at The University of Texas Health Science Center at San Antonio (UTHSC) and University of Florida. Their latest findings with ramifications for future studies of obesity, diabetes and eating disorders are reported in the June 29 issue of the international journal Nature.

The scientists, from UTHSC’s Research Imaging Center and Department of Physiology and UF’s Department of Psychiatry and Brain Institute, developed a new mathematical model for plotting the brain’s response to food. In a letter to Nature, they describe a study of 21 participants who drank orange-flavored sugar water while undergoing functional magnetic resonance imaging (functional MRI). Images were recorded for 10 minutes before consumption of the glucose and for 38 minutes afterward.

The mathematical model, called "temporal clustering analysis" or TCA, enabled the scientists to effectively determine time windows of brain activation—a statistical first step to more clearly showing which brain regions are involved in eating behavior.

"After eating, the human brain senses a biochemical change and then signals satiation, but precisely when this occurs is unknown," said corresponding author Jia-Hong Gao, Ph.D., associate professor of radiology at the Research Imaging Center. "The challenge of this functional MRI study was to map not only where but also when the brain responds following food ingestion."

The letter is titled "The temporal response of the brain after eating revealed by functional MRI." Co-authors are Peter T. Fox, M.D., director of the Research Imaging Center and professor of medicine, psychiatry and radiology at UTHSC; Ho-Ling Liu, a graduate student working under Dr. Gao’s supervision; and Yijun Liu, assistant professor at the UF Brain Institute and Department of Psychiatry.

Scans were completed at the Research Imaging Center. Head motion caused data from three subjects to be eliminated from the analyses. Some subjects agreed to a second scan in which they drank water rather than the sugar solution; the researchers later compared the brain’s response to each.

Brain regions activated after eating included the supplementary motor area, the somatosensory cortex, the cerebellum, the anterior cingulate and the orbitofrontal cortex. These regions may be involved in the integration of sensory and intuitive signals involved in appetite and taste and smell of food, the scientists concluded.

Blood samples were obtained at 15-minute intervals during the scanning and were analyzed for plasma insulin concentration. The scientists were excited to note that data from the functional MRI scans closely correlated with their measurements of the concentration of plasma insulin in the blood.

Overall, results were consistent with previous findings of the neural mechanisms underpinning control of eating behavior. "Although the exact role in regulating food ingestion remains to be established in humans, the temporal information may help us to understand how our brains generate a signal of satiety, both physiologically and psychologically," Dr. Fox said.

The study was limited to imaging of a single brain slice rather than the whole brain. The data therefore should be interpreted with caution, the researchers wrote.

The new mathematical model for brain response is an exciting breakthrough, the researchers said. "This TCA technique holds great potential in the study of the acute effects of medication and nutrition in the brain," Dr. Gao noted.

Contact: Will Sansom