Regenerative changes of voltage-dependent Ca2+ and K+ currents encode a learned stimulus association

Specific membrane current changes have been observed to persist on days following training with repeated paired presentations of light and rotation stimuli similar to those encountered by a nudibranch mollusc Hermissenda crassicornis in its natural habitat. Using a Pavlovian paradigm with light as a CS (conditioned stimulus) and rotation (approximating oceanic turbulence in the animal's natural setting) as a UCS (unconditioned stimulus), we showed that the animal acquired a learned behavioral change (a reduced ability to move toward a light source) which had most, if not all of the characteristic features of associative learning as it has been identified for advanced vertebrate species. The observed membrane current changes have been shown by a number of observations to play a causal role in acquiring and retaining associatively conditioned behavior of this animal. Regenerative interaction of synaptic and light-induced excitation and its underlying regeneratively interacting changes of Ca2+ and IA currents during acquisition lead to the long-lasting reduction of IA and other current changes which ultimately store for recall on subsequent days the previous occurrence of temporally associated light and rotation stimuli.