Unit of current and membrane resistance in Generalized Integrate-and-Fire model.
CloudyDory opened this issue · 2 comments
CloudyDory commented
Hi, in BrainPy's documentation on Generalized Integrate-and-Fire model, the model parameters and variables are:
**Model Parameters**
============= ============== ======== ====================================================================
**Parameter** **Init Value** **Unit** **Explanation**
------------- -------------- -------- --------------------------------------------------------------------
V_rest -70 mV Resting potential.
V_reset -70 mV Reset potential after spike.
V_th_inf -50 mV Target value of threshold potential :math:`V_{th}` updating.
V_th_reset -60 mV Free parameter, should be larger than :math:`V_{reset}`.
R 20 \ Membrane resistance.
tau 20 ms Membrane time constant. Compute by :math:`R * C`.
a 0 \ Coefficient describes the dependence of
:math:`V_{th}` on membrane potential.
b 0.01 \ Coefficient describes :math:`V_{th}` update.
k1 0.2 \ Constant pf :math:`I1`.
k2 0.02 \ Constant of :math:`I2`.
R1 0 \ Free parameter.
Describes dependence of :math:`I_1` reset value on
:math:`I_1` value before spiking.
R2 1 \ Free parameter.
Describes dependence of :math:`I_2` reset value on
:math:`I_2` value before spiking.
A1 0 \ Free parameter.
A2 0 \ Free parameter.
============= ============== ======== ====================================================================
**Model Variables**
================== ================= =========================================================
**Variables name** **Initial Value** **Explanation**
------------------ ----------------- ---------------------------------------------------------
V -70 Membrane potential.
input 0 External and synaptic input current.
spike False Flag to mark whether the neuron is spiking.
V_th -50 Spiking threshold potential.
I1 0 Internal current 1.
I2 0 Internal current 2.
t_last_spike -1e7 Last spike time stamp.
================== ================= =========================================================
It is unclear on the unit of membrane resistance and internal current (and possibly several other parameters and variables?). This may become a problem when using parameters of the GLIF neurons from other simulator which have explicit units.
chaoming0625 commented
Thanks for raising this issue.
CloudyDory commented
For reference: If we use parameters values from NEST (https://nest-simulator.readthedocs.io/en/stable/models/glif_psc.html), then I1
and I2
are in unit of pA, R
is in unit of GOhm, a
, b
, k1
and k2
are in unit of 1/ms. If we want to compute tau
from R * C
, then the membrane capacitance should be in unit of pF.