1. Time Cells in Hippocampal Area CA3
- Author
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Zoran Tiganj, Howard Eichenbaum, Annalyse Kohley, Marc W. Howard, Daniel M Salz, Srijesa Khasnabish, and Daniel J. Sheehan
- Subjects
0301 basic medicine ,Male ,Time Factors ,Journal Club ,Models, Neurological ,Hippocampus ,Action Potentials ,Spatial Behavior ,Cell Count ,Hippocampal formation ,Spatial memory ,03 medical and health sciences ,0302 clinical medicine ,Encoding (memory) ,Animals ,Humans ,Rats, Long-Evans ,Maze Learning ,CA1 Region, Hippocampal ,Spatial organization ,Neurons ,Communication ,business.industry ,Working memory ,General Neuroscience ,Articles ,CA3 Region, Hippocampal ,Temporal Lobe ,Rats ,030104 developmental biology ,Memory, Short-Term ,nervous system ,Temporal resolution ,Space Perception ,Exercise Test ,business ,Psychology ,Neuroscience ,030217 neurology & neurosurgery ,Coding (social sciences) - Abstract
Studies on time cells in the hippocampus have so far focused on area CA1 in animals performing memory tasks. Some studies have suggested that temporal processing within the hippocampus may be exclusive to CA1 and CA2, but not CA3, and may occur only under strong demands for memory. Here we examined the temporal and spatial coding properties of CA3 and CA1 neurons in rats performing a maze task that demanded working memory and a control task with no explicit working memory demand. In the memory demanding task, CA3 cells exhibited robust temporal modulation similar to the pattern of time cell activity in CA1, and the same populations of cells also exhibited typical place coding patterns in the same task. Furthermore, the temporal and spatial coding patterns of CA1 and CA3 were equivalently robust when animals performed a simplified version of the task that made no demands on working memory. However, time and place coding did differ in that the resolution of temporal coding decreased over time within the delay interval, whereas the resolution of place coding was not systematically affected by distance along the track. These findings support the view that CA1 and CA3 both participate in encoding the temporal and spatial organization of ongoing experience. SIGNIFICANCE STATEMENT Hippocampal “time cells” that fire at specific moments in a temporally structured memory task have so far been observed only in area CA1, and some studies have suggested that temporal coding within the hippocampus is exclusive to CA1. Here we describe time cells also in CA3, and time cells in both areas are observed even without working memory demands, similar to place cells in these areas. However, unlike equivalent spatial coding along a path, temporal coding is nonlinear, with greater temporal resolution earlier than later in temporally structured experiences. These observations reveal both similarities and differences in temporal and spatial coding within the hippocampus of importance to understanding how these features of memory are represented in the hippocampus.
- Published
- 2016