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Poster D in Poster Session D: Wednesday, August 5, 2:00 – 3:45 pm, Kimmel Center, Shorin & Rosenthal Rooms

Shallow Hippocampal Anticipation and Dopamine Responses During Evaluation of Novel Shortcuts

Gili Karni¹, Stephanie Crater², Yang-Sun Hwang², Tim Krausz², Alison E. Comrie³, Loren M. Frank², Joshua D. Berke², Nathaniel D. Daw¹; ¹Princeton University, ²University of California, San Francisco, ³HHMI Janelia Research Campus

Presenter: Gili Karni

When animals encounter new paths offering potential shortcuts, they must rapidly assess whether to pursue them. This evaluation likely involves mental simulation, but whether the brain performs exhaustive forward search or a cheaper, truncated approximation remains unclear. We recorded nucleus accumbens dopamine (DA; fiber photometry) and dorsal CA1 hippocampal activity (high-density electrophysiology) simultaneously in rats navigating a dynamic hexagonal maze in which barriers periodically changed location. Hippocampal decoded positions at new path encounters were biased forward but spatially local, concentrating on the newly available hex and the immediately adjacent location beyond it, with minimal representation of distant reward locations. DA responses were tightly aligned to hippocampal decoding of this adjacent location and were larger when it had been visited during the preceding block. These findings support truncated search: rapid evaluation of new spatial opportunities may rely on cached value at nearby locations rather than extended trajectory representation to reward.

Topic Area: Memory, Learning & Knowledge Structures