Repeated trains of electrical stimuli produce a late phase of long-term potentiation that lasts for more than a day. We found the properties of this phase, which previously had not been extensively explored, to be very similar to long-term facilitation of synaptic strength in Aplysia. In both Aplysia and mice, the late phase of long-term potentiation is strongly affected by modulatory interneurons, which in mice are recruited to switch a
