The Role of Noise in Brain Function Sisir Roy 1 & Rodolfo Llin´ as 2 1 Physics and Applied Mathematics Unit, Indian Statistical Institute, 203 Barrackpore Trunk Road, Kolkata 700108, India 2 New York University School of Medicine, 530 First Avenue, New York NY, 10016 USA 1 e-mail: sisir@isical.ac.in 2 e-mail: llinar01@med.nyu.edu Abstract Noise plays a fundamental role in all living organisms from the earliest prokaryotes to advanced mammalian forms, such as ourselves. In the context of living organisms, the term ’noise’ usually refers to the variance amongst measurements obtained from re- peated identical experimental conditions, or from output signals from these systems. It is noteworthy that both these conditions are universally characterized by the presence of background fluctuations. In non-biological systems, such as electronics or in commu- nications sciences, where the aim is to send error -free messages, noise was generally regarded as a problem. The discovery of Stochastic Resonances (SR) in non-linear dynamics brought a shift of perception where noise, rather than representing a prob- lem, became fundamental to system function, especially so in biology. The question now is: to what extent is biological function dependent on random noise?. Indeed, it seems feasible that noise also plays an important role in neuronal communication and oscillatory synchronization. Given this approach, it follows that determining Fisher in- formation content could be relevant in neuronal communication. It also seems possible that the principle of least time, and that of the sum over histories, could be important basic principles in understanding the coherence dynamics responsible for action and perception. Ultimately, external noise cancelation, combined with intrinsic noise signal embedding, and the use of the principle of least time, may be considered an essential step in the organization of central nervous system (CNS) function. Keywords : Stohastic Resonance, Quorum Sensing, Synchronization, Principle of Least Time . 1