Behavioral/Systems/Cognitive

nuates the amplitude of quantal synaptic voltages. These results demonstrate that Na amplify the synaptic voltage, enhancing the SNR and contrast sensitivity. Key words: retinal ganglion cell; contrast threshold; QX-314; tetrodotoxin; signal amplification; signal-to-noise ratio Introduction Voltage-gated membrane channels in a spiking neuron are necessary for spike generation, but they add noise to the spike train through several mechanisms. Their voltage gating is stochastic and therefore directly adds noise to the membrane current. In addition, below spike threshold, the voltage sensitivity of Na channels and the resulting modulation of regenerative currents can amplify noise from channels and synaptic inputs. This suggests that the function of voltage-gated channels is a trade-off between coding information and adding noise to the spike train (Schneidman et al., 1998; White et al., 2000; van Rossum et al., 2003). In a retinal ganglion cell, the spike generator limits the