Synaptic changes linked to associative learning are well known. Lamsa et al. examined long-term synaptic plasticity in different types of interneurons in rat hippocampal slices. They discovered an induction rule for long-term potentiation (LTP) that shows unusual characteristics. In contrast to known forms of plasticity, pairing synaptic input with hyperpolarization resulted in LTP, whereas pairing it with depolarization prevented it.
K. P. Lamsa, J. H. Heeroma, P. Somogyi, D. A. Rusakov, D. M. Kullmann, Anti-Hebbian long-term potentiation in the hippocampal feedback inhibitory circuit. Science 315, 1262-1266 (2007). [Abstract] [Full Text]