# What is the difference in amplitude and latency of IPSPs or EPSPs?

I'm building a Jansen & Rit whole brain model. In the original paper, it states:

A and B determine the maximum amplitude of the excitatory and inhibitory PSP (EPSP and IPSP), respectively, and a and b are the lumped representation of the sum of the reciprocal of the time constant of passive membrane and all other spatially distributed delays in the dendritic network. "

and

The A and B parameters of the PSP functions are proportional to the amplitude of the PSP. It is suggested that A = 3.25 mV and B = 22 mV (van Rotterdam et al. 1982). Certain neuropeptides modify the amplitude of the PSPs (Dodt et al. 1991), hence A and B have to be granted a degree of freedom. The a and b parameters of the PSP blocks are inversely proportional to the duration of the PSP. These are less likely to vary over relatively short periods, and therefore will be set to the same fixed values as used before (Jansen et al. 1993), namely, a = 100 s- 1 and b = 50 s- 1. The PSP blocks accounting for the delays in the intercolumn branches in the doublecolumn model will use the same A as the other PSP blocks, but ad = 30 S

I'm trying to find some sources that suggest B > A and b < a , as suggested here, but (van Rotterdam et al. 1982) is unfortunately not available for free, and I'm struggling to find anything else. Can somebody please explain why, according to this, the amplitudes of IPSPs are greater than EPSPs and similarly this latency discrepancy. Any sources would be very much appreciated. Thank you!

• I suspect the amplitude parts are just a part of how this particular model was designed; the "amplitude" of IPSPs is not really that meaningful in biology because most inhibition is shunting inhibition, but in modeling it can be simpler computationally to pretend like IPSPs are anti-EPSPs. Commented Jun 10 at 13:26
• As far as "latency", I wouldn't really describe this as "latency"; latency is the time until some event happens. The time part here corresponds to duration of a PSP; the differences between IPSPs and EPSPs would be from differences in gating: how long channels are open, how long neurotransmitter is bound, how long it takes for neurotransmitter in the synaptic cleft to diffuse away, be taken up by cells, or be chemically changed. Commented Jun 10 at 16:36