The study has revealed how the brain can connect discrete but overlapping experiences to provide a rich integrated history that extends far beyond individually experienced events and may help to direct future choices.
Usually, decisions are guided by drawing on past experiences, perhaps by generalizing across discrete events that overlap in content.
But, how such experiences are integrated into a unified representation was unclear, until now.
The researchers believe that such mechanisms involve the hippocampus, a brain structure closely linked with learning and memory. They also speculate the involvement of the midbrain, as its projections modulate activity in the hippocampus. And activity in both regions has been shown to facilitate encoding of individual episodes.
"We hypothesized that generalization stems from integrative encoding that occurs while experiencing events that partially overlap with previously encoded events and that such integrative encoding depends on both the hippocampus and midbrain dopamine regions. Further, we anticipated that greater hippocampal-midbrain engagement during integrative encoding enables rapid behavioral generalization in the future," said Dr. Daphna Shohamy from the Department of Psychology at Columbia University.
The researchers used functional magnetic resonance imaging to study participants engaged in an associative learning and generalization task.
They found that activity in the hippocampus and midbrain during learning predicted generalization and observed a cooperative interaction between the hippocampus and the midbrain during integrative encoding.
"By forming a thread that connects otherwise separate experiences, integrative encoding permits organisms to generalize across multiple past experience to guide choices in the present," explained Dr. Shohamy.
She added: "In people who generalize successfully, the brain is constantly building links across separate events, creating an integrated memory of life's episodes. For others, although the brain may accurately remember each past event, this integration does not occur, so that when confronted with a new situation, they are unable to flexibly apply what they learned in the past."
The study was published in the latest issue of the journal Neuron.