s . bi o - ph ] 1 1 A ug 2 00 3 Ensembles of Protein Molecules as Statistical Analog Computers ∗
نویسنده
چکیده
A class of analog computers built from large numbers of microscopic probabilistic machines is discussed. It is postulated that such computers are implemented in biological systems as ensembles of protein molecules. The formalism is based on an abstract computational model referred to as Protein Molecule Machine (PMM). A PMM is a continuous-time first-order Markov system with real input and output vectors, a finite set of discrete states, and the input-dependent conditional probability densities of state transitions. The output of a PMM is a function of its input and state. The components of input vector, called generalized potentials, can be interpreted as membrane potential, and concentrations of neurotransmitters. The components of output vector, called generalized currents, can represent ion currents, and the flows of second messengers. An Ensemble of PMMs (EPMM) is a set of independent identical PMMs with the same input vector, and the output vector equal to the sum of output vectors of individual PMMs. The paper suggests that much more complex computational resources are available at the level of individual neurons than those used in the traditional computational theories of neural networks. There is simply not enough neurons in the brain to replace the discussed statistical molecular computations by the statistical neural network computations. in press visit the web site www.brain0.com for information
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