Learning increases intrinsic excitability of hippocampal interneurons

Learning-related intrinsic excitability changes of pyramidal neurons via modulation of the postburst afterhyperpolarization (AHP)havebeenrepeatedlydemonstratedinmultiplebrainregions(especiallythehippocampus),afteravarietyoflearningtasks, and in multiple species. While exciting and important, the changes in pyramidal neurons are only a part of the neural circuitry involved in successful learning. For a more complete picture of the dynamic learning-related changes in the neural network, changesininhibitorycircuitrymustalsobesystematicallyexaminedandcharacterized.Hereweshowinyoungadultratsandmice that learning the hippocampus-dependent trace eyeblink conditioning task induces enhanced inhibition onto CA1 pyramidal neurons mediated, in part, by an increase in intrinsic excitability of somatostatin-positive inhibitory neurons (SOMs). Furthermore, both CA1 pyramidal and SOM interneurons shared a common cellular mechanism (reduction in SK channel-mediated AHP) that led to the learning-induced increased intrinsic excitability.