Paramecium learning: New insights

Abstract

Learning is a fundamental process that involves complex neural systems. However, microorganisms without a nervous system have also been shown to have learning abilities. Specifically, Paramecium caudatum has been reported to form associations between lighting conditions and cathodal shocks in its swimming medium. We replicated previous reports on this phenomenon and tested predictions of a molecular pathway hypothesis of paramecium learning.　In contrast to previous reports, our results indicated that paramecia can only associate higher light intensities with cathodal stimulation and cannot associate lower light intensities with cathodal stimulation. These results support the predictions of the previously proposed model of the molecular mechanisms of learning in paramecia, which depends on the effects of cathodal shocks on the interplay between cyclic adenosine monophosphate levels and phototactic　behavior in paramecia.