[NEST Users] STDP synapse t_spike and t_lastspike clarification

Dear all, I am trying to develop a new synapse model that uses the activity of the postsynaptic neuron. I'm looking at the STDP synapse to understand how it gets the target neuron history, and I wanted to clarify: are t_spike and t_lastspike the time stamps for the last spike of the presynaptic or postsynaptic neuron? I am looking at the send method of stdp_synapse.h (https://github.com/nest/nest-simulator/blob/91a02ed98017224deabe25e8e08bcfd…) Thanks in advance! Best, Priyanka Rao