Journal of Statistical Physics, Vol. 70, Nos. 1/2, 1993 Modulated Noisy Biological Dynamics: Three Examples Dante R. Chialvo 1 and A. Vania Apkarian 1 Three examples of noisy biological dynamics modulated by a periodic signal are discussed, A minimal neuron model driven by stochastic noise and small periodic force show a firing statistic comparable with stochastic resonance as demonstrated in bistable systems. Similar results are obtained from responses to periodic vibrotactile stimulation on higher-order neuronal units of the somatosensory pathway. Finally, results from a bistable visual perception task exhibiting stochastic resonance are reported. KEY WORDS: Stochastic resonance; spike generation; mechanoreceptors; spinal cord; somatosensory cortex; visual perception. 1. INTRODUCTION Appropriate encoding of information is a major task in the nervous system. Mechanisms by which sensory inputs are encoded and eventually decoded in the central nervous system have to take into account the presence of considerable uncorrelated background noise. This noise can be approx- imated by the ongoing spontaneous neuronal activity. The mean rate of the cellular spontaneous activity varies between regions of the brain and with states of arousal or wakefulness of the animal, yet to date, no concrete function is assigned to this activity. Recently, in an apparently unrelated context, it has been noticed that the output signal from a noisy bistable system can be modulated in time by applying a weak external periodic forcing.~l' 13) This phenomenon is curious in that an increase in the input noise can result in an improvement in the output signal-to-noise ratio. Since the optimum level of noise at which Computational Neuroscience, Department of Neurosurgery, SUNY Health Science Center, Syracuse, New York 13210. 375 0022-4715/93/0100-0375507.00/0 9 1993 Plenum Publishing Corporation