February 4, 2021
RIKEN
Keio University
A joint research team—led by Team Leader Shigeyoshi Fujisawa and Researcher Akihiro Shinpo of the RIKEN Center for Brain Science's Laboratory for Neurophysiology of Spatio-temporal Cognition, and Professor Eiichi Izawa of the Faculty of Letters, Keio University—has discovered using rats that neural circuits in the brain's hippocampus represent time information relatively.
These research findings are expected to contribute not only to elucidating the neural basis of time perception in animals and humans but also to understanding the neural basis of episodic memory, the memory of experienced events.
In recent years, a group of cells called "time cells," which fire in response to time intervals of several seconds, has been discovered in the hippocampus, a brain region central to spatial recognition. However, it was not clear what kind of temporal information these time cells respond to.
In this study, the joint research team trained rats on a task requiring time measurement and recorded neural activity from their hippocampus. They found that the hippocampal neurons did not represent absolute elapsed time—responding to a specific number of seconds from the start of the measurement—but rather responded to the proportion of elapsed time relative to the total measurement duration; in other words, relative elapsed time. Furthermore, they discovered that this cell population shares the same neurophysiological characteristics as the previously reported hippocampal cells that respond to spatial information. These results suggest that hippocampal cells represent spatial and temporal information using the same mechanism, which is considered crucial for understanding the neural basis of episodic memory that integrates "when, where, and what."
This research will be published in the scientific journal "Science Advances" on February 3 (February 4, Japan Standard Time).
Please see below for the full press release.