A hippocampal network for spatial coding during immobility and sleep

• Published in: Nature (London) Vol. 531; no. 7593; pp. 185 - 190
• Main Authors: Kay, Kenneth, Sosa, Marielena, Chung, Jason E., Karlsson, Mattias P., Larkin, Margaret C., Frank, Loren M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 10.03.2016; Nature Publishing Group
• Subjects: 631/378/1595/1554; 631/378/3920; Action Potentials; Animal cognition; Animals; Behavior; Brain; Hippocampus (Brain); Hippocampus - anatomy & histology; Hippocampus - cytology; Hippocampus - physiology; Humanities and Social Sciences; Male; Memory; Mobility; Models, Neurological; Movement; multidisciplinary; Neurons; Neurons - physiology; Observations; Orientation - physiology; Physiological aspects; Rats; Rats, Long-Evans; Science; Sleep; Sleep - physiology; Space Perception - physiology; Spatial Memory - physiology
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature17144

In the mammalian navigational system, neurons have been identified in the CA2 region of the hippocampus that keep track of position when an animal is not moving. How does an animal know where it is when it stops moving? Hippocampal place cells fire at discrete locations as subjects traverse space, thereby providing an explicit neural code for current location during locomotion. In contrast, during awake immobility, the hippocampus is thought to be dominated by neural firing representing past and possible future experience. The question of whether and how the hippocampus constructs a representation of current location in the absence of locomotion has been unresolved. Here we report that a distinct population of hippocampal neurons, located in the CA2 subregion, signals current location during immobility, and does so in association with a previously unidentified hippocampus-wide network pattern. In addition, signalling of location persists into brief periods of desynchronization prevalent in slow-wave sleep. The hippocampus thus generates a distinct representation of current location during immobility, pointing to mnemonic processing specific to experience occurring in the absence of locomotion. Knowing your place Decades of research have shown that the mammalian navigational system, based in and around the hippocampus, keeps track of an animal's location during locomotion. Yet it was not clear whether and how the brain tracks location when animals stop moving. This study shows that the brain keeps track of location at all times, on the move and at rest. Loren Frank and colleagues identify a distinct population of hippocampal neurons in the CA2 region of the hippocampus that signal current location not only during awake immobility, but also during sleep.