Internal stochastic resonance in the coherence between spinal and cortical neuronal ensembles in the cat.

Internal stochastic resonance is a phenomenon in which the coherence of a non-linear system is enhanced by the presence of a particular, non-zero level of noise generated by internal or external sources without a periodic input signal. The aim of this study was to demonstrate the experimental occurrence of internal stochastic resonance in the coherence between spinal and cortical neuronal ensembles. Simultaneous recordings of spinal and cortical evoked potentials were made in the somatosensory system of the anaesthetized cat. Evoked potentials were produced by input noise introduced in the tactile stimulation of the hindpaw skin. Coherence between the spinal and cortical evoked activity recorded during different levels of input noise was calculated. All animals showed distinct internal stochastic resonance like behavior. We found that the mean coherence was an inverted U-like function of the level of input noise with a mean coherence peak of 0.43. To our knowledge, this is the first documented evidence of such phenomenon in an in vivo preparation of the central nervous system.