Stochastic Resonance(SR) is a phenomena that a excitable system is capable of detecting weak signal best with some optimal noise strength. In usually case, the optimal noise strength is only one value (one maximum in the S/N versus noise strength plot). Since our environment is always changing, a crucial problem is that is the noise strength always in this optimal level ? Namely, for different environment, thus different noise strength, does our system automatically tune the excitability such that it is optimal ?