Long term potentiation is the process by which memories are encoded in the brain. It begins with $[$ Select $]["$stimuli$",$ "glutamate", "GABA", "dopamine"$]$ activating $[$ Select $]["$GABA$-$A receptors", "presynaptic neurons", "AMPA receptors", "NMDA receptors"$]$ and depolarizing the membrane. That causes the Mg$2+$ ion to pop out of the channel of the $[$ Select $]["$NMDA receptor", "GABA$-$A receptor", $"5$HT$2$A receptor", "AMPA receptor"$],$ allowing Ca$2+$ and Na$+$ to enter the cell. Ca$2+$ activates $[$ Select $]["$CREB and BDNF$",$ "Nitric oxide", "CaM$-$KII", "Nitric oxide synthase"$]$ which activates $[$ Select $]["$CaM$-$KII", "CREB and BDNF$",$ "nitric oxide synthase", "nitric oxide"$],$ producing NO$,$ which acts as a $[$ Select $]["$anterograde transmitter", "host substrate", "enzyme", "retrograde transmitter"$],$ causing increased release of neurotransmitter from the presynaptic neuron, resulting in sustained depolarization of the postsynaptic neuron.