Hi @mreynes. Many thanks for this report, there might have been some inadvertent change in Brian that cause this. When I recently answered another question here on the forum, I stated that " In fact, the on_event dictionary should only refer to pre and post, i.e. you can only set one event type for all pre and one event type for all post pathways." (How to activate synaptic pathways on custom events only? - #2 by mstimberg). I made this statement after looking at the code, but after having another look at the documentation (Custom events — Brian 2 2.7.0 documentation), it actually seems as if providing custom pathway names should be supported. Since your code uses this feature, and you had it work with Brian 2.5, so it seems to have been broken in an update. I’ll have a closer look soon and keep you posted!