This is the essence of learning. The lecturer says something, and it goes in one ear and out the other. The factoid is repeated; same thing. It's repeated enough times and--aha!--the lightbulb goes on and suddenly you get it. At a synaptic level, the axon terminal having to repeatedly release glutamate is the lecturer droning on repetitively; the moment when the postsynaptic threshold is passed and the NMDA receptors first activate is the dendritic spine finally getting it.