Activity-dependent synaptic plasticity is classically though to be the cellular substrate for learning and memory. Recent data show that activation of glutamate receptors initiates a long-term modification in pre- or post-synaptic neuronal excitability. Similarly to synaptic plasticity, intrinsic plasticity is bidirectional and input- or cell-specific. In addition to an increase in the reliability of the input-output function, temporal precision of the neuronal discharge is improved. These forms of plasticity not only share common learning rules and induction pathways with the better known synaptic plasticity but may also contribute in synergy with these synaptic changes to the formation of a coherent mnesic engram.