But in adults, food experiences appear to trigger more nuanced responses in the frontal cortex, the part of the brain that processes abstract thought associated with long-term goals, according to a neuroscientist with the University of Utah's Brain Institute.

It's more evidence that adolescent brains are still developing, which holds implications for early intervention in mental illness and for treatment of juvenile offenders.

"The adolescent brain responds differently to these rewarding cues than the adult brain," said Deborah Yurgelun-Todd, who uses magnetic resonance imaging (MRI) to study how stimuli affect brain activity, measured in terms of blood flow around the 3-pound organ.

Yurgelun-Todd presented her findings last week at the inaugural Lunch with Leo, a new lecture series The Leonardo will host with the Utah Science, Technology and Research initiative. USTAR recruited Yurgelun-Todd, a 25-year veteran of psychiatric research, to lead the U.'s Cognitive Neuroimaging Center with her husband, Perry Renshaw.

Yurgelun-Todd's work has been cited in Supreme Court arguments backing elimination of the death penalty for teens and is used by the Indiana juvenile justice system to reduce teen recidivism.

"The more we carry out this research the more we realize the brain is plastic, undergoing change throughout the lifetime," she said, noting that there is a general consensus that the brain reaches "adult" maturity around age 25.

The human brain reaches full size around age 5, but the organ keeps changing.

"The volume of the brain might not change but there is substantial remodeling during adolescence," Yurgelun-Todd said. It's that remodeling that her research seeks to understand.

For the food study, researchers put healthy people, both adolescents and adults who had no first-degree relatives with psychiatric disorders, into an MRI machine. They recorded changes in brain activity while exposing the subjects to 30-second glimpses of food and nonfood images.

The results were clear: Adolescents' responses to food were strictly subcortical.

This suggests youngsters' reward systems remain relatively unformed, which makes it harder if not impossible for them to understand long-term goals.

"Reward is incredibly important in goal-directed behavior. If your reward system is driving you to the extent that your inhibitions can't control impulse, you won't be able to control short-term gratification in favor of long-term goals," Yurgelun-Todd said.

bmaffly@sltrib.com