When a sitcom's laugh track stops and the camera pans seductively up the height of a glistening bacon cheeseburger, the teen brain snaps to attention - especially if that brain sits atop a body that carries excess fat, a new study says.
In teens with higher proportions of body fat, the brain's pleasure centers respond more robustly to fast-food advertising than they do in leaner teens, researchers have found. Even the regions of the brain that anticipate and process fast-food's sensory qualities send up a more robust response in fattier teens than in those with less fat.
The finding, published Thursday in the journal Cerebral Cortex, suggests the intriguing possibility that adolescents on a trajectory toward adult obesity "may simulate eating behaviors" when they are visually prompted by advertising, the study authors said. That "may then contribute to the enactment of the behavior itself," they added.
Repeated over time, those responses may all conspire to make weight loss harder later in life, they surmised.
A functional Magnetic Resonance Imaging scanner observed the subjects' brain responses to 24 advertisements - half featuring burgers, pizzas and chicken sandwiches marketed by fast-food giants, and half featuring such non-food products as laundry detergent, cars and insurance.
Despite subjects' rating the advertisements roughly equally exciting, the teens' brain scans found that, irrespective of body composition, they found the food advertisements more likely to arouse regions involved in attention, motivation, reward and pleasure.
But researchers found that while watching food ads, there was a clear correlation between a subject's degree of body fat and his or her activation in two key nodes of those circuits - the left-hemisphere's orbital frontal cortex and the right hemisphere's insula - as well as in the sensorimotor regions that process sensation from and plan movements of the lips, jaw and tongue.
The authors suggest that, in addition to having uncovered a possible neural mechanism that reinforces unhealthy eating habits, they may also have pointed to a strategy for promoting healthy long-term eating habits: stop watching the ads while enjoying "The Big Bang Theory" (and its ilk). For teenagers increasingly watching television where, when and however they like, that might already be second nature.