Figure 1. Neural representations of elapsed time in the hippocampus.

(A and B) When a cue (such as a specific sound; green) and an outcome (such as a puff of air directed at the eyes; blue) overlap in time (left) and drive overlapping neural activity in different groups of neurons (vertical green and blue lines), standard plasticity processes can account for learning. However, when the cue and the outcome are separated by more than ∼100 milliseconds (right), the mechanisms for linking these events in the brain are less well understood. (C) Modi et al. show that the time interval between the initial cue and the predicted arrival of the puff of air is bridged by temporally ordered sequences of activated neurons in hippocampal area CA1. (D) Ordered sequences are a common feature of activity in CA1, and can represent the animal’s trajectory in both time (left) and space (right).