  Many biological systems dynamically rearrange their components through a
sequence of configurations in order to perform their functions. Such dynamic
processes have been studied using network models that sequentially retrieve a
set of stored patterns. Previous models of sequential retrieval belong to a
general class in which the components of the system are controlled by a
feedback ("input modulation"). In contrast, we introduce a new class of models
in which the feedback modifies the interactions among the components
("interaction modulation"). We show that interaction modulation models are not
only capable of retrieving dynamic sequences, but they do so more robustly than
input modulation models. In particular, we find that modulation of symmetric
interactions allows retrieval of patterns with different activity levels and
has a much larger dynamic capacity. Our results suggest that interaction
modulation may be a common principle underlying biological systems that show
complex collective dynamics.
