Habituation in the Protozoan Spirostomum and Problems of Learning

  • P. B. Applewhite


The first thing to establish in studies on the molecular basis of memory is that the organisms chosen do, in fact, exhibit learning. This presents an immediate problem because a definition accepted by all is not available (Thorpe, 1963; Quarton et al., 1967; Hinde, 1970). More specifically, since we do not know what learning is from a chemical or physiological viewpoint we have difficulties in defining it precisely. For example, habituation is defined as a “waning of a response as a result of repeated stimulation” (Thorpe, 1963). If an addictive narcotic is given in a large enough dose to a person, he shows a behavioral response (euphoria) and repeated stimulation in the form of more doses eventually produces a waning of the behavioral response, i.e. his system has adapted to it. This certainly meets the definition of habituation but no one considers it a possible model system for learning. There is also the immunological response whereupon the second presentation of an antigen produces not only a larger titer of antibodies but also at a faster rate. This has been called immunological memory (Kabat, 1968) and certainly meets many definitions of memory but it too is not studied as a learning phenomenon. Why? The reason lies in the fact that “leaning and memory” are not precise enough terms to determine whether further study of phenomena agreeing with these definitions can be of any use in elucidating the molecular basis of learning and memory as psychologists and ethologists generally define it.


Mechanical Stimulus Habituation Behavior Large Titer Immunological Memory Repeated Stimulation 
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Copyright information

© Plenum Publishing Company Ltd. 1973

Authors and Affiliations

  • P. B. Applewhite
    • 1
  1. 1.Biology DepartmentYale UniversityNew HavenUSA

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