Figure 4.4-1A illustrates the response of the T-neuron when the two input pulses are separated by T = t2 = 3 ms. No output spike occurs. Trace 1 = v, 2 = x2 = epspl, 3 = x4 = epsp2. In Figure 4.4-1B, T = t2 = 2.05 ms. Again, no output spike. In Figure 4.4-1C, T = t2 = 1.0 ms. The peak v reaches the threshold phi = 0.355, and the RPFM neuron fires. Note that v resets to 0, then climbs again and falls back to zero. Trial-and-error simulation determines that this T-neuron model will fire when v(0) = 0 and T 3 2.0 ms.
Note that this RPFM model is not a strict T-neuron; it has "memory" because of the behavior of the LPF that conditions Vex to give v. The larger c is, the shorter the memory of the LPF. In general, if one considers the single-pole memory of the LPF, there will be a minimum instantantaneous frequency of a single input pulse train (the others being zero) below which there will be no output pulses. Thus, for a single input channel, the T-neuron model above behaves like a highpass filter.
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