# Description of problem

hi there, I am new to Brian2 so apologies if this is an obvious mistake.

I am trying to run an LIF networks where I can explicitly add current to two variables I_e (external current) and I_i (internal current) which are then added onto the voltage in the model at each step.

As a test to see that this is working correctly I have simply added the inputs from I_e and I_i to the current voltage, using the equations provided from Brian2 LIF examples and compared the spikes. But weirdly when I do this the results look quite different - I was wondering if I am incorrectly assigning my variables?

# Minimal code to reproduce problem

**here is my model:**

lif ="""

dv/dt = -(V-v_rest) / t_tau : 1 (unless refractory)

V = v + I_e + I_i : 1 #combine current voltage with incoming currents

I_i : 1 #internal current

I_e : 1 #external current"""

**here is the model i am trying to reproduce** - if my equation is doing what it should be doing the output should be the same

lif = ââ"

dv/dt = -(v-v_rest) / t_tau : 1 (unless refractory)"""

# What you have already tried

i think the error may be to do with how I am adding current to my I_i and I_e variables.

In the online examples i can see that internal weights are accumulated to the voltage variable, via on_pre as âv+=wâ.

Given that I am adding I_i onto v in my equation I have changed this to on_pre: âI_i = wâ

Similarly for the Poisson input group the target_var from the online examples was âtarget_var = vâ, which I have changed to âtarget_var = I_eâ

One thing in particular I have noticed is that it seems like the I_e variable accumlates current from previous time steps when it should just add the current from the input from that time step alone - I am not sure how exactly to fix this?

Any thoughts on why the equations are not doing the same thing would be much appreciated!

Thanks!