Paramecium Learning: New Insights and Modifications

Abstract

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.

Where association ends. A review of associative learning in invertebrates, plants and protista, and a reflection on its limits.

“…The results revealed that the paramecia in the experimental group spent more time near the side that had been paired with the cathode, either illuminated or dark, than the other groups. Alipour et al (2018) partially replicated the results of Armus et al (2006). They observed how paramecia linked high light intensities with cathodic shocks, but not dark stimulation.…”

“…From the early studies by Jennings (1904, 1906) to the most recent ones (Alipour et al, 2018), the same pattern can be detected about learning research in this eukaryote. The early work suggested that learning in paramecia had occurred, but subsequent authors questioned the results by arguing the lack of control for several variables.…”

“…Recent studies with plants, although promising, are not conclusive. Conditioning preparations show serious difficulties in building associations at the unicellular level, given that the only work that can be considered as evidence of conditioning is the one by Armus et al (2006), as replicated by Alipour et al (2018). Although more associative experiments can and should be done (it is evident that the interesting results by Gelber (1952Gelber ( , 1958 and Hennessey et al (1979) should be replicated), this current study-though containing negative results-is already an important scientific achievement that should be taken into account by association psychologists.…”

“…In essence, there are three studies presenting outstanding results on Associative Learning in paramecia (see Table 3 for a summary): Gelber (1952, 1958), a polemic result which has not been successfully replicated; Hennessey et al (1979), which was never replicated; and Armus et al (2006), which produced an artifactual result as the light-dark counterbalance was not properly analyzed. However, Alipour et al (2018) confirmed that there can be an association between intense light and cathodic stimulation in paramecia…”

Integrative Neuroscience ofParamecium, a “Swimming Neuron”

“…Thus, after training, Paramecium spends more time than before in the lighted compartment. This interpretation is supported by the observation that the "trained" behavior only occurs when the cathodal compartment is lighted during training (Alipour et al, 2018), and by the absence of retention (Mingee, 2013).…”