ABSTRACT
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Cells have limited views of their surroundings. ey are able to sense various chemical and physical properties of their immediate environment, but distal information can come only through stochastic processes, such as diusion of chemicals. Cells lack the ability to sense directly distal parts of their environment, as humans can through vision and hearing. us, we might expect that cells have adopted memory of the past as a way of accumulating information about their environment and so gain an advantage in their behavior. In a simple application, memory can be used to track how environmental signals change over time. For example, in the chemotaxis network of Escherichia coli, cells use memory of previous measurements of chemical concentrations to estimate the time derivative of the chemical concentration and thus to infer whether the organism is swimming up or down a chemical gradient [2]. Conversely, memory can be useful in enabling persistent behavior despite changing environments. For example, dierentiated cells in a multicellular organism must remain dierentiated and not redierentiate despite existing under a variety of conditions. If such cells become damaged or infected, they may undergo apoptosis, but we do not observe neurons becoming liver cells, or liver cells becoming muscle cells, and so on.
