Thermodynamic limits to information harvesting in sensory systems
Stefano Bo, Nordita.
To be able to survive and prosper, cells need to acquire, exchange and process information under noisy conditions.
Recording multiple measurements is an effective way of reducing the noise. It is known in general that handling
information has a thermodynamic cost. Inspired by this biological problem and in view of the relation between
information and thermodynamics we investigate how much information about an external protocol can be stored
in the memory of a stochastic measurement device given an energy budget. We consider a layered device with
a memory component storing information about the external environment by monitoring the history of a sensory
part coupled to the environment. We derive an integral fluctuation theorem for the entropy production and a measure
of the information accumulated in the memory device. Its most immediate consequence is that the amount of
information is bounded by the average thermodynamic entropy produced by the process. At equilibrium no entropy
is produced and therefore the memory device does not add any information about the environment to the sensory
component. Consequently, if the system operates at equilibrium the addition of a memory component is superfluous.
Such a device can be used to model the sensing process of a cell measuring the external concentration of a chemical
compound and encoding the measurement in the amount of phosphorylated cytoplasmic proteins.