Figure 2.

Potential role of synaptogenesis in circuit formation and dynamics. A, Schematic depiction of how synaptic remodeling may lead to the formation of a neuronal engram. During learning, strong inputs to the circuit from various upstream areas leads to the activation of select neurons. Activity triggers synaptic remodeling, with formation of new connections between neurons activated together while also potentially pruning away connections between neurons not activated together. This may connect neurons that previously did not interact with one another. Consolidation then proceeds to strengthen the new and preexisting connections between engram neurons while eliminating some connections with other neurons. The strong interconnectivity between engram neurons subsequently allows weaker and incomplete inputs to trigger complete reactivation of the neural engram and allow for memory recall. B, Example illustrating one way that synaptogenesis may reshape coactivity dynamics between neurons within a circuit. Before learning, neurons within a circuit may not be connected or share the same inputs. This results in their activity being largely independent of each other and uncorrelated. Following learning-induced formation of new synaptic connections between them, the activity of one of the neurons becomes dependent on the other, resulting in correlated dynamics. Such changes throughout an entire circuit may lead to dramatic changes in the neuronal coactivity patterns.