Linnea Herzog

 Katz and Jadhav Labs

“Reorganization and reactivation of a preexisting taste-responsive hippocampal network”

Once an animal has located a source of delicious food, they will return to the same place again and again. Ms. Herzog reports on her work measuring activity in the rat hippocampus, an area of the brain that includes cells that respond to a particular location, known as place cells. These cells become more specified in rats as they find areas with food they prefer.

Animals need to remember the locations of nourishing and toxic food sources for survival, a fact that necessitates a mechanism that can associate taste experiences with particular places. We have previously identified such responses within hippocampal place cells, whose activity is thought to aid memory-guided behavior by forming a mental map of an animal’s environment that can be reshaped through experience. However, it remains unknown whether taste-responsive place cells and their spatial properties are preconfigured or emerge as a result of taste experience, and how this experience reorganizes spatial maps. Here, we recorded from single units in the dorsal CA1 hippocampal region of rats running for taste rewards delivered via intra-oral cannulae at specific locations on a linear track. We found that even before taste experience itself, taste responsiveness was inherent in a subset of cells that had larger place fields than non-taste-responsive cells overlapping with stimulus delivery zones. Taste-responsive cells’ place fields then contracted to be more restricted to stimulus delivery zones following taste exposure, leading to a stronger representation of rewarded areas on the track. These remapped units exhibited increased sharp-wave ripple (SWR) co-activation during the taste delivery session, which correlated with the degree of place field contraction. Our results suggest that taste responsivity is preconfigured in a subset of hippocampal place cells, whose spatial representations are refined by sensory experience. This could be a possible mechanism by which animals identify and remember locations where ecologically relevant sensory stimuli are found within their environment.