How does the brain accumulate cognitive maps?

Project Summary
Across our lifetimes we have an infinite number of experiences that are stored in our memories. As we age our
capacity to reuse this information to influence our future learning decreases, leading to impaired cognitive and
behavioral flexibility. Cognitive decline is a major concern for an increasingly large and aging population, and
these cognitive deficits will directly impact quality of life for countless individuals. It is essential to understand the
neuronal coding deficits underlying cognitive decline to provide the necessary groundwork for developing
therapeutic interventions that can spare people from cognitive decline. It has been postulated that the brain uses
cognitive maps, or internal neural representations, to enable flexible behavior and relate items in our memory.
The discovery of neurons in the hippocampus that fire action potentials in specific locations within an
environment, termed place cells, provided initial support for the cognitive map hypothesis, as these cells create
a neural representation of the environment. Both the engram and spatial navigation literatures have shown that
distinct cognitive maps are used to encode two different environments, which would presumably reduce
interference between maps during recall. However, recent work suggests that linking two distinct memories
neuronally can enhance memory strength by sharing neural resources. Due to this linking, recall of one memory
leads to a higher probability of recalling the other. This implies that some aspects of the two cognitive maps have
increased in similarity and are no longer distinct. Others have hypothesized that increased similarity between
cognitive maps may link experiences across environments and provide a mechanism to increase learning rates.
Indeed, more recent evidence showed that neuronal representations in dCA1 became more similar as mice
increased their speed of learning novel problems, suggesting that, under certain conditions, cognitive maps in
the hippocampus may become increasingly similar, impacting learning. I will utilize in vivo calcium imaging with
miniature microscopes as young adult and middle-aged mice navigate four distinct circular tracks for water
rewards to ask the question of whether the similarity between neural representations underlying cognitive maps
changes as mice increase their learning rates in novel environments. By using separate measurements of
representational similarity, I can provide a detailed account of how the brain encodes new cognitive maps and
whether the brain relates cognitive maps to alter learning rates. By using young adult and middle-aged mice, I
can determine if these mechanisms change during aging. All results from this proposal have the capability to
inform us on how the brain uses stored information to influence our future learning and, ultimately, how these
mechanisms change during the early stages of cognitive decline.

Grant Number: 5F31AG087649-02
NIH Institute/Center: NIH
Principal Investigator: Austin Baggetta