Model 2a, Input Sensitivities
Sensitivity tests performed on the input components of model 2a revealed acute dependence of the spike number response on the ratio between the electrical and chemical synapse amplitudes of both the EOCD and primary afferent inputs. Decreasing the input amplitude of either electrical synapse by 25%, with a correspoding increase in the NMDA mediated EPSP amplitude to maintain a non-zero number of resulting spikes, completely abolished the graded response as a function of delay (not shown). However, a sensitivity test performed on t -decay for the chemical synaptic inputs revealed a sharpening of temporal acuity (figure 20) as EPSP decay time approached the 3ms value typically used to model AMPA PSPs (Gabbiani et al., 1994). This is consistent with the rapid decay of granular cell chemically mediated EPSPs as recorded in vivo, intracellularly in primary afferent fibers (Bell and Grant, 1992). For these reasons, the inputs to model 2a were modified and maximum conductance values were recalibrated.
