Biological Threshold Function

[Ashley Aitken]

G'day,

In browsing literature to help construct a simple information processing model
of (biological) neurons I have seen little discussion of the threshold
function - that is, how the threshold (membrane potential) of a neuron 
changes.

I understand that there is a refractory period after each particular action
potential pulse (which effectively represents a change in the threshold
value, and hence limits the burst frequency) and their is a period of
super-excitability after this.  However, I am interested in changes
on a larger timescale.

Is there local change in the threshold value (c.f. the biases in artificial 
neural networks) on a larger timescale ?

Is there any global modulation of the threshold values of groups of neurons 
(say in an area of the cortex) ?

If anyone has any comments or references relevant to these questions I 
would be most grateful if they could email them to me - I will 
summarize if there is interest and a good response.

Regards,
Ashley Aitken.

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