Stochastic resonance improves signal detection in hippocampal CA1 neurons

Stochastic resonance (SR) is a phenomenon observed in nonlinear systems whe reby the introduction of noise enhances the detection of a subthreshold sig nal for a certain range of noise intensity. The nonlinear threshold detecti on mechanism that neurons employ and the noisy environment in which they re side makes it likely that SR plays a role in neural signal detection. Altho ugh the role of SR in sensory neural systems has been studied extensively, its role in central neurons is unknown. In many central neurons, such as th e hippocampal CAI cell, very large dendritic trees are responsible for dete cting neural input in a noisy environment. Attenuation due to the electroto nic length of these trees is significant, suggesting that a method other th an passive summation is necessary if signals at the distal ends of the tree are to be detected. The hypothesis that SR plays an important role in the detection of distal synaptic inputs first was tested in a computer simulati on of a CA1 cell and then verified with in vitro rat hippocampal slices. Th e results clearly showed that SR can enhance signal detection in CAI hippoc ampal cells. Moreover, high levels of noise were found to equalize detectio n of synaptic signals received at varying positions on the dendritic tree. The amount of noise needed to evoke the effect is compared with physiologic al noise in slices and in vivo.