Multiple mechanisms of expression of LTP. A. Early in development synapses may acquire NMDA receptors before AMPA receptors (so-called silent synapses). B. The unsilencing of silent synapses is likely to involve the synaptic insertion of AMPA receptors. C. Complementary evidence exists showing that functional synapses can increase their synaptic strength via an increase in p(r) PPP = paired-pulse potency. D. There is also evidence for an increase in the quantal size due to the synaptic insertion of AMPA receptors exhibiting, paradoxically, lower γ. E, F. Increases in quantal size, due to an increase in γ (E) or in the number of AMPA receptors (F) have also also been observed.