FIGURE 6.

A. Model of generation of time cell firing by interaction of two theta rhythmic neurons. Cell 1 (top) fires at a slightly higher fixed difference in frequency relative to the theta rhythmic firing of Cell 2 (middle). The two cells start out of phase with each other and gradually approach the same phase of firing (Cell 1 and Cell 2). When they fire at the same phase, they drive the spiking of a Time Cell (arrow), that codes the time from the onset of firing. B. Time cells allow disambiguation of different memories involving overlapping spatial trajectories in a simulation of a behavioural task using virtual hallways with items in each hallway (Brown et al., 2010). In a simulation (Hasselmo, 2012), items are represented by different icons. One item (cue triangle) in a start hallway (Start1) can cue retrieval of a full spatiotemporal trajectory that ends with the correct turn into the final hallway (End1). A different item (cue circle) in a different start hallway (Start2) can cue retrieval of a different spatiotemporal trajectory that shares spatial locations, but uses different time cells to code the different trajectory, allowing correct turn into the correct final hallway (End2).