v_init in McIntyre axon model

[tonyclick]

Hello all,
I'm working on the research in electrical stimulation based on McIntyre axon model 2002.
I found automatic generation of action potentials without stimulus ，when I changed the value of v_init both in MRGaxon.hoc and MRGaxon.ses

Code: Select all

proc model_globels() {
	celsius=37
	v_init=-75 //mV//     > -75 self original :-80
	dt=0.005 //ms//
	tstop=10

I also changed e_pas

Code: Select all

STIN[i]{
			nseg=1
			diam=fiberD
			L=interlength
			Ra=rhoa*(1/(axonD/fiberD)^2)/10000
			cm=2*axonD/fiberD
			insert pas
			g_pas=0.0001*axonD/fiberD
			e_pas=v_init   //-80
			insert extracellular xraxial=Rpx xg=mygm/(nl*2) xc=mycm/(nl*2)
			}

in README, 20141009 Nikki Pelot tidied up the code by changing e_pas = v_init to
e_pas = -80 in three lines (number 93, 106, 119) in MRGaxon.hoc.

I'm confused whether v_init can't be changed？


Could someone assist me with that?

Thanks.
Regards

[ted]

First, to help me decide how best to answer your question, here's a question for you: have you ever done any wet-lab neuroscience, or is your background entirely mathematics/physics/engineering/computer science?

[tonyclick]

First, to help me decide how best to answer your question, here's a question for you: have you ever done any wet-lab neuroscience, or is your background entirely mathematics/physics/engineering/computer science?

Dear Ted,
Thanks for your attention ！I am a new graduate student, studying in biomedical engineering. I have carefully read some papers related to the MRG model.
Core article:

McIntyre CC, Richardson AG, and Grill WM Modeling the excitability ofmammalian nerve fibers: influence of afterpotentials on the recovery cycle. Journal of Neurophysiology 87:995-1006, 2002.

resting potential =-80mV，from following paper:

Bostock, H., and J. C. Rothwell. "Latent addition in motor and sensory fibres of human peripheral nerve." The Journal of physiology 498.1 (1997): 277-294.

But I haven't found the specific value of resting potential in that.
Meanwhile, I have reviewed v_init of other models in ModelDB:

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-70

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-70

https://senselab.med.yale.edu/ModelDB/S ... ses#tabs-2
v_init=-75

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-85.9411

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-70

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-69.77 -70

https://senselab.med.yale.edu/ModelDB/S ... ses#tabs-2
v_init=-65

https://senselab.med.yale.edu/ModelDB/S ... hoc#tabs-2
v_init=-60

So I changed the v_init in the MRG model to find out its influence, and then I got previous questions

[ted]

That particular model was implemented for the purpose of studying initiation and propagation of action potentials along a myelinated axon. If one were performing the corresponding experiment on a real myelinated axon, one would wait until the axon and surrounding tissues have recovered from the trauma produced by the dissection needed to expose it and place stimulation and recording electrodes. Actual application of stimuli and recording of responses would begin only after a sufficiently long interval has passed for the axon and surrounding tissue to reach a stable resting state.

A computational model of this experimental arrangement has its own state variables whose values must be properly initialized before a simulation is launched. By tinkering with v_init, you are perturbing the model away from the steady state that the model's developer(s) worked so hard to discover and implement in their source code. That's fine, do whatever you like, but don't be surprised when the results are different from those that the model authors report in their papers.