Strange problem during fitting process: is it a bug of nrn?
Posted: Mon Dec 19, 2011 3:25 pm
I have a mechanism in my model which calculates amplitude of EPSPs for me. I have non-uniform model so I have to initialize my model to the steady state (when t<0). My synapse become active at t = 10. this is my mechanism.
I have a simple fitting tool which tries to find the weight of synapse in which EPSP become a specific value.
Now my problem #1 is that when I change conductance of one of my channels from 3 to 1.5, EPSP amplitude reported by the above mechanism become a fixed value for different values of synaptic weight. when I plot the membrane potential I can see that for different values of synaptic weight different EPSP is produced in the model. Also, when I use a vector mechanism to record the membrane potential and then find the maximum value of membrane potential I can calculate value of EPSPs.
However, the vmax mechanism always report a fix value for amp when conductance of my channel is 1.5 or 2 or 1.7. then again when I change the conductance of the channel to 3, vmax mechanism works fine.
I am really confused. It seem there is sth wrong.
Problem #2 When I change morphology of my neuron, variable time step tool cause similar problem reported above.
If you want my idea, I think there is nasty bug in the neuron or my vmax mechanism.
Code: Select all
NEURON {
SUFFIX vmax
RANGE vm, tm, vrest, amp
}
ASSIGNED {
v (millivolt)
vm (millivolt)
vrest (millivolt)
amp (millivolt)
tm (ms)
}
INITIAL {
reset(v)
}
PROCEDURE reset(v (mV)) { : callable from hoc
vm = v
vrest = v
amp = 0
}
BREAKPOINT {
if (v>vm && t>9.9) {
vm=v
tm=t
}
if (t>1 && t<9.9) { vrest = v }
amp = vm - vrest
}
Now my problem #1 is that when I change conductance of one of my channels from 3 to 1.5, EPSP amplitude reported by the above mechanism become a fixed value for different values of synaptic weight. when I plot the membrane potential I can see that for different values of synaptic weight different EPSP is produced in the model. Also, when I use a vector mechanism to record the membrane potential and then find the maximum value of membrane potential I can calculate value of EPSPs.
However, the vmax mechanism always report a fix value for amp when conductance of my channel is 1.5 or 2 or 1.7. then again when I change the conductance of the channel to 3, vmax mechanism works fine.
I am really confused. It seem there is sth wrong.
Problem #2 When I change morphology of my neuron, variable time step tool cause similar problem reported above.
If you want my idea, I think there is nasty bug in the neuron or my vmax mechanism.