 Here, f’s firing appears to be a cause of e’s firing (along with p). If f hadn’t fired, then the switch s would have been set to the left, so e would not have fired. So f’s firing was needed for e to fire. However, there doesn’t seem to be any difference between the process leading from f’s firing to e’s firing in this system of neurons and the process leading from f’s firing to e’s firing in the original system of neurons.