Light-guided running behavior induces direction selective spikes of hippocampal neurons

[Speaker] Yuki Aoki:1
[Co-author] Hideyoshi Igata:1, Takuya Sasaki:1,2, Yuji Ikegaya:1
1:Lab. Chem. Pharmacol., Grad. Sch. Pharmaceut. Sci., Univ. Tokyo, Japan, 2:Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Japan

The hippocampus consists of place cells that preferentially show spike activity when animals visit a limited area of the environment. A widely used behavioral task for characterizing place cells is a foraging task in which rats freely explore an open two-dimensional space in search of randomly dispersed food pellets. In this task, firing of place cells tends to be largely independent of movement direction. On the other hand, in spatial task on radial arm maze and linear track where animals develop goal-directed behavioral strategies, place-selective firing of hippocampal cells is biased in a specific direction of movement. Thus, the hippocampal circuit employs distinct encoding modes for space depending on ongoing task demands and the presence of goals. In this study, we recorded the firing patterns of hippocampal cells, and the rats performed goal related tasks and random foraging tasks in open field. In the goal-related task, the rat had to run towards a light-cued goal to obtain a food reward in the field. Enhancing the degree of freedom of moving directions by utilizing the two-dimensional space allowed us to analyze animal's trajectories from various provenance toward goals, including errors, which could not be parsed in a stereotyped one-dimensional path, such as a linear track. We found a certain population of hippocampal cells in the goal-directed task fired only while rats approached to a specific future goal independent of moving directions. These goal-directed place-selective firing cells showed similar firing patterns to those observed in the same locations in the foraging task only when the animals ran fast. In the random foraging task, these cells also showed goal-directed activity by accelerating their firing rates as a function of their speeds when the animals moved to the goal location. The evidence advances our understanding of how place-selective firing of hippocampal cells is modified by goal-directed movement in an open field.
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