After six days, the rats no longer received a reward for choosing the center hole. They were divided into four test groups, each with an equal number of adults and adolescents: rats that were given 20 percent less food between sessions and received the light cue; rats that received the light cue but could eat as much as they liked between sessions; a group that received less food and no light cue; and a group that could eat between sessions but was not shown the light cue during the experiments.
Moghaddam and her team found that adolescents tended to return to the center hole far more often than the adults although they received no reward and continued going to the hole long after the adult rats stopped altogether. Such doggedness was even more prominent in adolescents who received the light cue and had a restricted diet before the experiment. This group nosed the center hole 30 times, twice as often as adults under the same circumstances and as adolescents with less food and no light cue. Adolescents that received the cue and had free access to food made for the center hole only a third as often.
Thus, rats experiencing internal and external stimuli-hunger and the light cue-compulsively sought the earlier reward long after the other rats realized it no longer existed. These results suggest that human teenagers can similarly behave irrationally and compulsively when faced with certain feelings and settings, Moghaddam said. "A scenario could range from the relatively mundane, such as hungry teenagers being more likely than adults to buy fast food immediately after seeing an advertisement, to despair and relationship problems eliciting thoughts of suicide," she said.
For the project's next phase, the Pitt group will repeat the experiments while monitoring activity in the emotion and cognition centers of the adolescent and adult rats' brains, Moghaddam said. This information will help Moghaddam and her colleagues grasp how brain cells encode the behavioral signals sent in response to stimuli.
Source: University of Pittsburgh