Brain areas active while learning hierarchical structure of a problem There are multiple examples in the machine learning literature of trying to learn the hierarchical structure of a reinforcement learning problem, however have there been any papers tying this learning to neurological activity in the brain?

The type of evidence I would like some indication of a neural substrate indicating some type of activity when learning a hierarchical structure is necessary to solve a problem vs. when a simple problem is attempted.
According to "Frontal Cortex and the Discovery of Abstract Action Rules" by David Badre, Andrew S. Kayser, and MarkD'Esposito:


  ... the rostro-caudal axis of frontal cortex support rule learning at
  higher levels of abstraction. Moreover, these results indicate that
  when humans confront new rule learning problems, this rostro-caudal
  division of labor supports the search for relationships between
  context and action at multiple levels of abstraction simultaneously.


They found this by contrasting fMRI signals collected while the subject performed two tasks, one requiring a hierarchical, abstract rule and one requiring a flat, basic mapping.