Inconsistency about refractory period with Brian Simulator

[ghost]

In my opinion, implementation of refractory period in Brian Simulation makes more sense.

Assume refrac_period = 1

Bindsnet
t=0: mem+=input --> neuron spikes --> refrac = 1
t=1: refrac = 0 --> mem+=input --> neuron spikes 

Ref:
https://github.com/Hananel-Hazan/bindsnet/blob/6d4a7a7980080556c79c34d2a603bada12dc78d0/bindsnet/network/nodes.py#L324-L334

Brian simulation
t=0: mem+=input --> neuron spikes --> t_spike = 0
t=1: t_current - t_spike < refrac_period  --> do nothing
t=2: t_current - t_spike > refrac_period --> mem+=input --> neuron spikes --> ...

Ref:
https://github.com/brian-team/brian2/blob/2b8e459798bd84be1c01e707d74993f2f260b5ce/brian2/groups/neurongroup.py#L121

[djsaunde]

Good point. How would you fix this? Feel free to open a PR.

[ghost]

Since there is a definition of t in network/init, one possible way is to add t as an additional argument to step function. Inside the step function, introduce new variable to store spiking time (say t_spike). Everytime step function is called, check if t-t_spike is greater than refractory period and do operation accordingly.

[djsaunde]

Hm, that could be problematic when doing multiple simulations in sequence. For example:

network.run(inpts, time=100)
network.run(inpts, time=100)  # Forgets refractory neurons from end of previous simulation!

Alternatively, one could just reverse the ordering, from:

# Decrement refractory counters.
self.refrac_count[self.refrac_count != 0] -= dt 

# Integrate inputs. 
self.v += (self.refrac_count == 0).float() * inpts 
  
# Check for spiking neurons.
self.s = self.v >= self.thresh

# Refractoriness and voltage reset. 
self.refrac_count.masked_fill_(self.s, self.refrac) 

to

# Integrate inputs. 
self.v += (self.refrac_count == 0).float() * inpts 
  
# Decrement refractory counters.
self.refrac_count[self.refrac_count != 0] -= dt 

# Check for spiking neurons.
self.s = self.v >= self.thresh

# Refractoriness and voltage reset. 
self.refrac_count.masked_fill_(self.s, self.refrac) 

Does this make sense? Does this appear to solve the problem?

[ghost]

Yes, that will be better than my solution.

[ghost]

You may need to be careful when changing order. There are models (like this) that do self.refrac_count == 0 more than once.

[djsaunde]

Solved by #136.