Stochastic and coherence resonance in hippocampal neurons

Stochastic resonance (SR) is a phenomenon observed in nonlinear systems whereby the introduction of noise enhances the detection of subthreshold signals. Both computer simulations and experimental recordings in the hippocampal brain slice have shown that stochastic resonance could play a significant role to enhance the detection of synaptic potentials generated in distal synapses. The noise variance required to improve synaptic detection in CA1 neurons is well within the physiological range of the noise generated by endogenous sources. Intracellular recordings in CA1 pyramidal cells confirmed that subthreshold signals could be detected with the generation of small amplitude endogenous noise in single cells. Computer simulations have been applied to test the hypothesis that the effect of stochastic resonance is enhanced when the noise and subthreshold signals are applied to several neurons at the same time. Computer simulation of the coupled network of hippocampal neurons did reveal a marked improvement in signal detection when independent noise sources were applied to multiple neurons. However, the addition of noise to a coupled neuronal network also revealed the appearance of synchronized neural activity similar to epilepsy. This recently observed phenomenon, known as coherence resonance, is responsible for the appearance of spontaneous neuronal activity and decreases the signal to noise ratio of subthreshold synaptic inputs.