where <math>t_{sp}</math> denotes the spike time and <math>U</math> is the increment of <math>u</math> produced by a spike. We denote as <math>u^-, x^-</math> the corresponding variables just before the arrival of the spike, and <math>u^+</math> refers to the moment just after the spike. From the first equation, <math>u^+ = u^- + U(1-u^-)</math>. The synaptic current generated at the synapse by the spike arriving at <math>t_{sp}</math> is then given by | where <math>t_{sp}</math> denotes the spike time and <math>U</math> is the increment of <math>u</math> produced by a spike. We denote as <math>u^-, x^-</math> the corresponding variables just before the arrival of the spike, and <math>u^+</math> refers to the moment just after the spike. From the first equation, <math>u^+ = u^- + U(1-u^-)</math>. The synaptic current generated at the synapse by the spike arriving at <math>t_{sp}</math> is then given by |