Assimilation of newly learned category features in the ventromedial prefrontal-anterior hippocampus system

Humans update their knowledge about the world throughout their lifetimes, but few category learning studies have examined how people can add new information to a previously learned category, a process that Piaget termed "assimilation". We collected fMRI data while participants learned new features for a previously learned family resemblance category structure. Previous research using this task has found that participants typically develop abstract prototype representations in the ventromedial Prefrontal Cortex (VMPFC) and anterior hippocampus during this task, which may rely on schematic memory representations supported by this system. In the first part of the study, before acquisition of new features, a majority of participants used a prototype strategy and overall prototype representations were present in VMPFC and anterior hippocampus. In the second part of the study, in which participants learned new features, the VMPFC and anterior hippocampus were more active during learning than during the first part. Furthermore, in a following transfer test participants who categorized using a prototype strategy showed prototype representations in VMPFC and the anterior hippocampus. In contrast, exemplar representations recruited regions of the parietal cortex around the intraparietal sulcus and the caudate nucleus. These results indicate that abstract category representations such as prototypes can rely on complex declarative memory representations such as schemas that are supported by the VMPFC-anterior hippocampus system, and that this system can flexibly assimilate new feature information to the category representation over time.