Figure 5.

Molecular mechanisms of consolidation. After the encoding of a memory (the encounter of food in a Y-maze, upper panel), memory undergoes a series of processes that allow its consolidation into long-term memories resistant to the passage of time. Engram synapses (purple, middle panel) undergo synaptic plasticity changes (late phase of long-term potentiation [or late-LTP]). Triggered by the intracellular increase in Ca²⁺, adenylyl cyclase is activated and the intracellular concentration of cAMP increases. The cAMP increase triggers the activation of protein kinase A (PKA) and mitogen-activated protein kinases (MAPKs). PKA translocates to the nucleus, phosphorylates the transcription factor CREB, and ultimately triggers the transcription of genes containing CREB-responsive element (CRE), such as immediate early genes (c-fos, Arc, or Zif268), kinases such as Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and protein kinase Mzeta (PKMζ). In the dendrites, protein synthesis occurs locally by ribosomes translating mRNAs in a localized manner in the dendritic spines.