Memory decay is rapid at first and slower later-a feature that accounts for Jost's memory law: that old memories gain on newer ones with lapse of time. The rate-sensitive property of habituation-that recovery after spaced stimuli may be slower than after massed-provides a clue to the dynamics of memory decay. Rate-sensitive habituation can be modeled by a cascade of thresholded integrator units that have a counterpart in human brain areas identified by magnetic source imaging (MSI). The memory trace component of the multiple-time-scale model for habituation can provide a 'clock' that has the properties necessary to account for both static and dynamic properties of interval timing: static proportional and Weber-law timing as well as dynamic tracking of progressive, 'impulse' and periodic interval sequences.