on the output of neuron i which is here called the presynaptic output and the output of neuron j which is going to be the post synaptic output the rule the kind of mantra here is the fire together wire together means that if two neurons are active at the same time regularly then they probably should be connected together because they already correlate and you can see right here that there is a term in this formula that is o i times o j so this here is the correlation between or the covariance um or just the product