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The Journal of Neuroscience, December 15, 2002, 22(24):11019-11025

Enhancement of Signal-to-Noise Ratio and Phase Locking for Small Inputs by a Low-Threshold Outward Current in Auditory Neurons

Gytis Svirskis^{1, 2}, Vibhakar Kotak¹, Dan H. Sanes¹, and John Rinzel^{1, 3}

¹ Center for Neural Science, New York University, New York, New York 10003, ² Laboratory of Neurophysiology, Biomedical Research Institute, Kaunas Medical University, 3000 Kaunas, Lithuania, and ³ Courant Institute of Mathematical Sciences, New York University, New York, New York 10012

Neurons possess multiple voltage-dependent conductances specific for their function. To investigate how low-threshold outward currents improve the detection of small signals in a noisy background, we recorded from gerbil medial superior olivary (MSO) neurons in vitro. MSO neurons responded phasically, with a single spike to a step current injection. When bathed in dendrotoxin (DTX), most cells switched to tonic firing, suggesting that low-threshold potassium currents (I_KLT) participated in shaping these phasic responses. Neurons were stimulated with a computer-generated steady barrage of random inputs, mimicking weak synaptic conductance transients (the "noise"), together with a larger but still subthreshold postsynaptic conductance, EPSG (the "signal"). DTX reduced the signal-to-noise ratio (SNR), defined as the ratio of probability to fire in response to the EPSG and the probability to fire spontaneously in response to noise. The reduction was mainly attributable to the increase of spontaneous firing in DTX. The spike-triggered reverse correlation indicated that, for spike generation, the neuron with I_KLT required faster inward current transients. This narrow temporal integration window contributed to superior phase locking of firing to periodic stimuli before application of DTX. A computer model including Hodgkin-Huxley type conductances for spike generation and for I_KLT (Rathouz and Trussell, 1998) showed similar response statistics. The dynamic low-threshold outward current increased SNR and the temporal precision of integration of weak subthreshold signals in auditory neurons by suppressing false positives.

Key words: medial superior olive; signal-to-noise ratio; phase locking; computer model; potassium conductance; slice recordings

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Copyright © 2002 Society for Neuroscience  0270-6474/02/222411019-07$05.00/0

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