Previous work by Kandel had led to the discovery of a set of serotonin-secreting interneurons in the tail of <em>Aplysia</em>, the activation of which could enhance the gill-withdrawal reflex (4).  Application of both serotonin and its associated second messenger cAMP to the connections between sensory and motor neurons was found to close single potassium ion channels in <em>Aplysia</em> sensory neurons, accounting for an increase in the duration of action potentials that leads to sensitization (5).  In 1985, research showed that the cAMP-dependent phosphorylation was essential for sensitization of the <em>Aplysia</em> gill-withdrawl reflex (6).  The fast neurotransmitter release caused by serotonin and/or cAMP application is associated with short-term facilitation.  This paper outlines the role of CREB and gene transcription in long-term facilitation, setting the stage for future research elucidating the entire memory cascade.