In contrast to manipulations of maximum ionic conductances for the various channels, change in input amplitude is a parameter of the model that is expected to directly control the predicted relationship between spike number and delay. Accordingly, as a final test on the preliminary model, the amplitude of constant current injection was varied between 96.49% and 400% of the default level (figure 5d). Spike number was found to decrease in a discontinuous manner as injected current amplitude was decreased by between 0 and 4% from the default level. Spike number decreases at increasing current amplitudes were markedly less sensitive, although it is expected that such a spike number decrease in the biological granular cell is due to decreasing levels of summated input depolarization as opposed to increasing, I-NaF saturating depolarization.

Attempts to produce a burst of variable spike number (see figure 6 for experimental values) depending on the latency between two AMPA/NMDA mediated EPSPs and an I_clamp simulating the primary afferent electrical synapse with these default conductance levels failed due to a lack of regenerative spiking. Realistic cellular inputs such as these produced a two spike output of variable onset latency, regardless of the delay between inputs (not shown). This initial failure to replicate experimental results describing the relationship between input delay and granular cell spike number (figure 6) indicated the necessity for modifications of ionic conductances and synaptic inputs in subsequent models.

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