Custom events¶
In most simulations, a NeuronGroup
defines a threshold on its membrane
potential that triggers a spike event. This event can be monitored by a
SpikeMonitor
, it is used in synaptic interactions, and in integrate-and-fire
models it also leads to the execution of one or more reset statements.
Sometimes, it can be useful to define additional events, e.g. when an ion
concentration in the cell crosses a certain threshold. This can be done with
the events
keyword in the NeuronGroup
initializer:
group = NeuronGroup(N, '...', threshold='...', reset='...',
events={'custom_event': 'x > x_th'})
In this example, we define an event with the name custom_event
that is
triggered when the x
variable crosses the threshold x_th
. Such events
can be recorded with an EventMonitor
:
event_mon = EventMonitor(group, 'custom_event')
Such an EventMonitor
can be used in the same way as a SpikeMonitor
– in
fact, creating the SpikeMonitor
is basically identical to recording the
spike
event with an EventMonitor
. An EventMonitor
is not limited to
record the event time/neuron index, it can also record other variables of the
model:
event_mon = EventMonitor(group, 'custom_event', variables['var1', 'var2'])
If the event should trigger a series of statements (i.e. the equivalent of
reset
statements), this can be added by calling run_on_event
:
group.run_on_event('custom_event', 'x=0')
When neurons are connected by Synapses
, the pre
and post
pathways
are triggered by spike events by default. It is possible to change this by
providing an on_event
keyword that either specifies which event to use for all
pathways, or a specific event for each pathway (where non-specified pathways use
the default spike
event):
synapse_1 = Synapses(group, another_group, '...', on_pre='...', on_event='custom_event')
synapse_2 = Synapses(group, another_group, '...', on_pre='...', on_post='...',
on_event={'pre': 'custom_event'})
Scheduling¶
By default, custom events are checked after the spiking threshold (in the
after_thresholds
slots) and statements are executed after the reset (in
the after_resets
slots). The slot for the execution of custom
event-triggered statements can be changed when it is added with the usual
when
and order
keyword arguments (see Scheduling and custom progress reporting for details).
To change the time when the condition is checked, use
NeuronGroup.set_event_schedule()
.