Modulation of hippocampal plasticity in learning and memory

Synaptic plasticity plays a central role in the study of neural mechanisms of learning and memory. Plasticity rules are not invariant over time but are under neuromodulatory control, enabling behavioral states to influence memory formation. Neuromodulation controls synaptic plasticity at network level by directing information flow, at circuit level through changes in excitation/inhibition balance, and at synaptic level through modulation of intracellular signaling cascades. Although most research has focused on modulation of principal neurons, recent progress has uncovered important roles for interneurons in not only routing information, but also setting conditions for synaptic plasticity. Moreover, astrocytes have been shown to both gate and mediate plasticity. These additional mechanisms must be considered for a comprehensive mechanistic understanding of learning and memory. •Hippocampal theta-gamma and sharp wave-ripple states show distinct types of plasticity.•These states are associated with acetylcholine and dopamine release in the hippocampus.•Neuromodulators can control plasticity via input selection in neuronal circuits.•Modulation of excitation-inhibition balance can control plasticity by affecting spike patterns.•Astrocytes as synaptic modulators of plasticity are affected by extrinsic neuromodulators.