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

Learning is a cornerstone of intelligent behavior in animals. This behavior has been mostly studied in organisms with a fairly complex nervous system. However, recent reports of learning in unicellular organisms suggested the existence of associative learning in unicellular organisms. In particular, the capability to associate different light intensities with cathodal stimulation in paramecium is of special interest. We have investigated the previous reports on this phenomenon and proposed a molecular mechanism for learning behavior in paramecium. Specifically, we have used the existing evolutionary evidence in order to find the possible molecular pathways that may play a role in Paramecium's learning. Moreover, previous studies have been reviewed in order to propose new experiments that can verify the plausibility of the present hypothesis.