ИСТИНА

Aims Hippocampal place cells are an object of highlighted interest in neuroscience. Their place-specific firing patterns (place fields) constitute so-called cognitive maps which can retain for days[1,2], but also can be remapped in environment-dependent manner. However, the principles driving the formation of the cognitive map in a novel environment remain unclear. Here we focus on the first moments of the exploration of a completely novel context, and define a critical time for cognitive map tuning by means of miniscopic neuronal recordings. Methods Twelve male C57BL6 mice aged at least 2 month were taken for this study. Mice underwent two surgical stereotaxic operations under anesthesia: first, viral vector particles coding various fluorescent calcium indicators (GCaMP6, NCAMP7) under CAG promoter were injected to the field CA1 of the hippocampus. Then, after 2 week recovery, mice were subjected to GRIN-lens implantation above the microinjection site. After another 2 weeks mice were checked for a fluorescent calcium signal and baseplates for NVista HD miniscope were mounted on the scull surface. Finally, awake mice with attached NVista HD miniscopes were put into a novel environment: circular O-shaped track with visual cues on surrounding curtains. Mice spent 15 min exploring the track while neuronal calcium signal and behavior video tracking were captured. Locations and traces of neurons were extracted from neuronal video data with MIN1PIPE routine and then place fields were detected by means of surface approximation in angle-time domain. For each place field a tuning time was defined post hoc as amount of time spent before a correspondent place cell begin repeatedly fire in the field. Results Most of animals demonstrated rapidly tuned cognitive maps with uniform distribution of place fields, covering all sectors of the track. Spatial selectivity of the cognitive map was shown by means of dimensionality reduction methods: the in-track locations of animals were successfully decoded from neural activity. Place fields showed average tuning time around 140 seconds. More than 30% place cells get tuned within the first in-track lap, while more 60% place cells do it within the first 3 laps along the track. Conclusions Taken together, these results suggest that cognitive maps form uniformly and rapidly not only in time domain, but also in spatial domain. This can provide a background for the searching for early behavior or intrinsic triggers for a cognitive map formation. Acknowledgements This study was funded by RSF grant #20-15-00283, RFBR grants #20-015-00427 and #19-04-00395 and by Russian Ministry of Science and Higher Education Project # 075-15-2020-801. References 1. Ziv Y., Burns L. D., Cocker E. D., Hamel E. O., Ghosh K. K., Kitch L. J., El Gamal A., Schnitzer M. J. (2013). Long-term dynamics of CA1 hippocampal place codes. Nature neuroscience, 2013, 16(3), 264–266. https://doi.org/10.1038/nn.3329 2. Rubin A., Geva N., Sheintuch L., Ziv Y. Hippocampal ensemble dynamics timestamp events in long-term memory. Elife, 2015, 4, e12247. https://doi.org/10.7554/eLife.12247