Summary: Researchers implicate the hippocampus in conceptual memory formation. The study reveals activity within the hippocampus and ventromedial prefrontal cortex is consistent with the retrieval of new concepts.
Source: University of Oregon.
If your idea of a perfect dog is an abstract rendering of canine qualities extracted across many encounters in your life, you are not alone in how your brain connects memories, say University of Oregon scientists.
A long debate has existed in psychology whether concepts, such as a dog, are represented in the mind as a collection of specific dogs that people have encountered or whether individuals can abstract the key characteristics across specific examples to form a generalized idea, or prototype, of a dog.
Without knowing all the dogs someone has seen before, it may be difficult to tell whether people can recognize a new animal as a dog because they rely on a comparison to specific dogs or rather their prototype.
Knowing more about the ability to build abstract memories, the researchers said, could help educators develop new strategies for teaching concepts.
In an experiment aimed to uncover how concepts are represented in the brain, 29 participants, ages 18-28, first viewed several novel cartoon animals as examples from two different concept categories whose members were related to families called Romeo or Juliet. Researchers then used functional MRI to watch the brains of participants as they viewed new, previously unseen cartoon animals and chose which family was the best match for each.
Responses revealed that participants must have formed and relied on abstract representations – the prototypes — of the new concepts, reported Caitlin Bowman and Dagmar Zeithamova of the UO’s Department of Psychology in the March 7 issue of the Journal of Neuroscience.
The fMRI data allowed them to follow processing across the brain as decisions were made. They documented activity in the anterior hippocampus and ventromedial prefrontal cortex that was consistent with a retrieval of the prototype rather than specific concept examples. This finding suggests the hippocampus — previously considered a filing system for specific memories of individual events — has a role in conceptual memory formation.
“There have been doubts whether or not memories can be generalized, abstract representations that are more than just collections of specific items,” said Zeithamova, a psychology professor who heads the Brain and Memory Lab. “There have been very few studies that have looked at the brain to try to tease this out.”
Previous studies have tried but failed to find evidence for abstract concept representations in the brain, probably because of their approaches, said Bowman, a postdoctoral researcher in Zeithamova’s lab.
“We found that having enough consistency, enough similarity across new experiences, contributed to building abstract thinking,” Bowman said. “If you only use penguins and flamingos as examples of birds, it may be impossible to form a coherent concept of a bird.”
In the project, done in the UO’s Robert and Beverly Center for Neuroimaging, the researchers used artificial creatures as stimuli to examine what features subjects processed and remembered, Bowman said.
Following training, participants went through a series of trials while in the MRI scanner. New creatures were presented with a slightly differing color, shape of the body, head, feet or tail, orientation of dots on the body, neck patterns or directions the heads faced.
“We watched conceptualization in action,” Bowman said. “We found that people form these abstract memories by linking across different examples. While the hippocampus has been thought to only represent individual memories, here it seems to work with the ventromedial prefrontal cortex to create these abstract memories.”
It may be, Zeithamova said, that the hippocampus allows people to generalize.
“You recognize a newly seen creature is a dog, because it looks like your neighbor’s dog or like the one that bit you the other day,” she said. “This may allow you to remember specific events but also helps you put them together.”
The findings provide fundamental new knowledge about how memory works, Zeithamova said, and eventually could lead to new strategies in educational settings that help students to consolidate new information with previously learned material to build stronger cognitive maps of various topics.
“Traditionally, we’ve thought that there was a division of labor between memory systems that allow us to remember specific individual events versus those that allow us to generalize across multiple events,” she said. “We show here that the hippocampus contributes to the generalization of concepts and works with the ventromedial prefrontal cortex in real time to organize experiences according to their similarities and differences.”
Funding: The National Institutes of Health, through a grant from the National Institute on Aging to Bowman, funded the research together with funding from the Lewis Family Endowment, which supports the Lewis Neuroimaging Center.
Source: Jim Barlow – University of Oregon
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Caitlin Bowman.
Original Research: Abstract for “Abstract Memory Representations in the Ventromedial Prefrontal Cortex and Hippocampus Support Concept Generalization” by Caitlin R. Bowman and Dagmar Zeithamova in Journal of Neuroscience. Published March 7 2018.
Abstract Memory Representations in the Ventromedial Prefrontal Cortex and Hippocampus Support Concept Generalization
Memory function involves both the ability to remember details of individual experiences and the ability to link information across events to create new knowledge. Prior research has identified the ventromedial prefrontal cortex (VMPFC) and the hippocampus as important for integrating across events in the service of generalization in episodic memory. The degree to which these memory integration mechanisms contribute to other forms of generalization, such as concept learning, is unclear. The present study used a concept-learning task in humans (both sexes) coupled with model-based fMRI to test whether VMPFC and hippocampus contribute to concept generalization, and whether they do so by maintaining specific category exemplars or abstract category representations. Two formal categorization models were fit to individual subject data: a prototype model that posits abstract category representations and an exemplar model that posits category representations based on individual category members. Latent variables from each of these models were entered into neuroimaging analyses to determine whether VMPFC and the hippocampus track prototype or exemplar information during concept generalization. Behavioral model fits indicated that almost three-quarters of the subjects relied on prototype information when making judgments about new category members. Paralleling prototype dominance in behavior, correlates of the prototype model were identified in VMPFC and the anterior hippocampus with no significant exemplar correlates. These results indicate that the VMPFC and portions of the hippocampus play a broad role in memory generalization and that they do so by representing abstract information integrated from multiple events.
SIGNIFICANCE STATEMENT Whether people represent concepts as a set of individual category members or by deriving generalized concept representations abstracted across exemplars has been debated. In episodic memory, generalized memory representations have been shown to arise through integration across events supported by the ventromedial prefrontal cortex (VMPFC) and hippocampus. The current study combined formal categorization models with fMRI data analysis to show that the VMPFC and anterior hippocampus represent abstract prototype information during concept generalization, contributing novel evidence of generalized concept representations in the brain. Results indicate that VMPFC–hippocampal memory integration mechanisms contribute to knowledge generalization across multiple cognitive domains, with the degree of abstraction of memory representations varying along the long axis of the hippocampus.