# EPSP/IPSP amplitude values?

I'm working with a Hodgkin-Huxley model that receives synaptic inputs from presynaptic neurons. If it receives a spike from an excitatory presynaptic neuron, the voltage of my HH neuron inceases by an amount $g$. If it receives a spike from an inhibitory neuron, the voltage jumps down by an amount $g \times K$ (so K is the factor controlling how much the voltage drops relative to how much it would increase from an excitatory neuron). I read in textbooks that the ratio of excitatory:inhibitory neurons is generally $4:1$. That implies that for the system to be "balanced", I should have $K=4$. If $K<4$, then there is a net drift upwards in voltage towards the threshold values, and for $K>4$, there is a net drift downwards away from the threshold.

I have two sub-questions:

1) Is there a typical value of $g$ (the EPSP amplitude) that is biologically plausible? I've seen anywhere from $0.1-0.5$ and above which is quite a big range. I know that there is often a big range based on stimulus and whatnot, but I'm looking for a biologically reasonable value.

2) What is a typical value of $K$? In other words, what is the size of a typical IPSP amplitude relative to the EPSP amplitude? I've seen anywhere from the amplitude being the same to the amplitude being 4x the EPSP amplitude (which of course is a mighty big range).

• this question is based on a misunderstanding that should be clarified here: cogsci.stackexchange.com/questions/8206/… – honi Jun 3 '16 at 17:12
• also, g is conductance, not a magnitude of voltage change. the amount of voltage change due to a particular conductance value depends on the driving force of that conductance. – honi Jun 3 '16 at 17:14
• what resource are you using? – honi Jun 3 '16 at 17:15
• @honi Sorry, I think $g$ was just bad notation (I should probably use $Q$ instead or something other than $g$). I was looking at these papers: arxiv.org/pdf/cond-mat/0608552v1.pdf (Eq 2) and link.springer.com/article/10.1140%2Fepjb%2Fe2012-30282-0 (bottom right of page 2) – Brenton Jun 3 '16 at 20:22
• I'm not sure why you would use Hodgkin-Huxley neurons if you are not using conductance based inputs... The whole point of the HH model is that it is in terms of conductances. – honi Jun 5 '16 at 1:41