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sychology

Protozoan Learning

A substantial number of investigators are currently involved in the search for the physiological and chemical correlates of learning. Progress in this area will certainly result from and initiate the development of sophisticated measuring systems. Equally important in promoting advances in research may be the selection of organisms for study. As Applewhite and Morowitz (1967) stated, "If we want information about memory at the fine structural and molecular level, an experimental organism must be chosen that allows this information to be found (p. 329)." As the virus was instrumental to molecular genetics, perhaps choice of a less complex organism will accelerate progress in unravelling the physio-chemical correlates of learning.

A series of experiments (Beck, 1975) was conducted to determine if a protozoan, Spirostomum Ambiguum, could serve as a viable model for investigating the molecular basis of learning. Habituation was the type of learning examined in these studies. Habituation is defined as a response decrement resulting from repetitive stimulation not due to injury, fatigue, or adaptation.

Response probabilities were found to decrease with repetitive stimulation. Also, habituation became successively more rapid with repeated series of habituation training and spontaneous recovery. Beck concluded that the response of Spirostomum to repetitive stimulation exhibits a strong behavioral similarity to the habituation of metazoans. Thus, it appears that at least some species of protozoa have memory and are able to learn or modify their behavior as a result of experience.
 

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