Synaptic Noise Improves Detection of Subthreshold Signals in Hippocampal CA1 Neurons

Abstract

Stochastic resonance (SR) is a phenomenon whereby the detection of a low-level signal is enhanced in a nonlinear system by the introduction of noise. Studies of the effects of SR in neurons have suggested that noise could play a prominent role in improving detection of small signals. Most experimental SR research has focused on the role of noise in sensory neurons using physiological stimuli. Computer simulations show that signal detection in hippocampal neurons is improved by the addition of physiological levels of noise applied extracellularly to synaptic inputs. These results were confirmed experimentally. We now report that endogenous noise sources can also improve signal detection. The noise source was generated by modulating the random synaptic activity on the apical dendrites of CA1 cells in rat hippocampal slices using subthreshold cathodic current. Intracellular recordings of CA1 cells showed that even small increases of synaptic noise are able to greatly improve the detection of an independent, synaptic, subthreshold stimulus as predicted by the simulations. The noise variance in the CA1 cell was compared with the resting variance and with variance changes caused by several endogenous noise sources. In all cases, the increased noise variance was well within the physiological range. These results were supplemented and analyzed with a CA1 computer model. The improved signal detection with small amounts of endogenous noise suggests that the diverse inputs to CA1 are able to improve detection of subthreshold synaptic signals and could provide a means to modulate detection of specific inputs in the hippocampus.

Intrinsic Noise in Cultured Hippocampal Neurons: Experiment and Modeling

“…In vivo, the activity is more marked by "noisy" firing of presynaptic neurons (Pare et al, 1998;Destexhe et al, 2001Destexhe et al, , 2003Fellous et al, 2003), which further overwhelms the contribution from stochastic ion channels. Such network states have recently been proposed as mechanisms for gain modulation (Chance et al, 2002;Mitchell and Silver, 2003), enhanced signal detection (Ho and Destexhe, 2000;Stacey and Durand, 2001), contrast invariance tuning (Anderson et al, 2000), and more (for a thorough review, see Destexhe et al, 2003). However, this type of background activity is active and may be categorized as extrinsic to the neuron.…”

Noise-Controlled Signal Transmission in a Multithread Semiconductor Neuron

“…Considerable progress in this direction was recently reported in [3][4][5] where semiconductor p-n wires were shown to provide a suitable medium for the transmission of electrical pulses in the manner of biological neurons. However, an essential feature of real neurons is their ability to function in a stochastic environment [6,7], and, in particular, to exploit the power of random noise to enhance the propagation of useful signals along their axons [8,9]. It is important to reproduce this property in hardware in order to create a realistic neuronlike structure.…”

Stochastic and coherence resonance in hippocampal neurons

“…]. This phenomenon was observed intracellularly and the noise required to generate this effect is well within the physiological noise amplitude know to be present within neurons [2]. However, neurons are arranged in arrays and the effect of SR could be enhanced significantly when both noise and signals are applied to many neurons.…”