Model 1b, Overview
Although chemically mediated EPSPs delivered onto the granular cell have yet to be described intracellularly, intracellular recordings from the innervating primary afferent suggest that the major component of these EPSPs is more similar to a fast AMPA-like PSP rather than the slow, NMDA-like PSP primarily represented in this model (figure 1 vs. figure 7, Bell and Grant, 1992).
Furthermore, use of chemically mediated EPSPs with faster t -decay values seemed likely to alleviate the need for the experimentally unverified EOCD electrical synapse input component. A sensitivity test on model 1a that tested chemical synaptic input components with t decay values ranging between 3 and 40ms revealed a dramatic sharpening of the burst duration response as the EPSP became more similar to a fast, AMPA-type depolarizing input (figure 12). Thus, model 1a was ill-equiped to handle more biologically realistic AMPA-type synaptic inputs, and was therefore modified to produce a similar spike number relationship to input delay relationship under updated input conditions (figure 13).
