Article Figures & Data
Figures
- Fig. 1.
The firing properties of MSO neurons.A, In response to a step current injection, MSO neurons showed outward rectification and only a single spike when the stimulus exceeded the threshold (phasic firing). The steady-state current–voltage curve (inset) generated from the responses to step current stimuli showed that low-threshold outward rectification appeared near the resting membrane potential. Several spontaneous IPSPs were observed in these traces. The same properties suppressed firing in response to a slow triangular current-ramp stimulus, whereas faster stimuli evoked single spikes (C). B, After an application of DTX, the cells fired tonically and responded with spikes to a slow current-ramp stimulus (D). E, In a more mature (P17) MSO neuron, outward current was activated at more hyperpolarized potentials, as can be seen in the current–voltage relationship (inset). F, DTXK did not induce tonic firing in the same neuron but lowered the spike threshold. The spike was evoked by the same current used for thebottom trace in E. Note the afterdepolarization (arrow) after the spike and the absence of an undershoot (dotted arrows; compareE, F) after the step stimulus. These effects indicate that IKLT was blocked by DTXK. The calibration in B and D are the same as in A and C, respectively.A and B are from the same P14 neuron.C and D are from the same P12 neuron.
- Fig. 2.
The firing statistics of a P17 MSO neuron in response to weak and noisy stimuli. A, Traces of membrane potential illustrating random and signal evoked firing.B, The PSTH for the response to a subthreshold EPSP signal in the presence of smaller random excitatory and inhibitory input transients. The EPSG, generated by dynamic clamp, in addition to the random input caused a sharp increase in the probability to fire. DTX increased the spontaneous firing rate and thereby reduced the SNR several times (inset shows difference of PSTH probability from baseline and then divided by baseline).C, Spike-triggered reverse correlation exhibited a hyperpolarizing component followed by excitation in control conditions. In the presence of DTX, an average spike-evoking current developed slower. The error bars mark the SD for the injected current; thex symbol denotes the mean current value. The average over a population of seven neurons of the mean injected current (over trials as in C) for before (D) and after (E) application of DTX or DTXK have similar properties as for a single neuron. The error bars mark the SD (shown only below the average) for each time point. The baselines were subtracted. F, The PSTH and period histogram (inset) showed phase-locked firing to a periodically modulated stimulus. After DTX, the vector strength of phase locking decreased by nearly one-half.
- Fig. 3.
Statistical response properties of a model with Hodgkin-Huxley type conductances.A, The PSTH for a subthreshold EPSG in the presence of random input. The low-threshold outward current reduced the spontaneous firing rate to 2 Hz but increased the signal-to-noise ratio (inset). B, The spike-triggered reverse correlation had the same shape as for the recorded neurons, with a hyperpolarizing component and faster dynamics for the spike-evoking current in the model withIKLT. The traces were normalized, and baselines were subtracted to compare more easily the time course shapes. a.u., Arbitrary units.C, Vector strength (VS) versus frequency, for periodically modulated stimulus. The model withIKLT phase locked more strongly at each frequency.
- Fig. 4.
Influence ofIKLT on the integration of small signals with different amplitude and in the presence of noise with various strengths. A, The ratio of the probabilities to generate a spike attributable to the signal spontaneously decreases when the amplitude a of the random EPSGs increases. Note that the increase of SNR by IKLT is strongest for the weakest noise. B, The probability to generate a spike in response to the signal calculated as an integral of rate larger than spontaneous rate. Both curves have non-monotonic shape, reflecting some optimal noise strength for signal detection. C, The ratio of probabilities increases when the amplitude of the signal grows. TheIKLT effect is strongest for the largest amplitude.
- Fig. 5.
Influence of IKLTproperties on small-signal integration in the model. A, Very slow IKLT activation increases spontaneous activity, whereas very fast activation suppresses strongly both the response to the signal and spontaneous activity. ParametersA0 and B0 were changed to speed up or slow down the activation ofIKLT. B, Spike-triggered reverse correlation shows fastest current transients for the model withIKLT having intermediate activation rate.C, When IKLT is replaced by an increased leak conductance in the model, the SNR is little changed, although suppression of the response was stronger withoutIKLT.
