Prior attempts to condition a one-celled organism, paramecium, by either classical or instrumental procedures have yielded both positive and negative results. As the results of those studies may be subject to several interpretations other than one indicating learning, it was decided to use a more traditional technique for the present study. This experiment was designed to assess whether aversive electric shock could be used to train paramecia on a brightness discrimination task, a procedure that has been used in animal learning research. The results indicated that such learning may have occurred.
"At the time the author of this experiment did not provide a definitive mechanism by which this could occur other than to suggest that paramecia have the capacity to avoid a less than suitable environment. Fast-forward 100 years and it is now apparent that paramecia are able to learn to discriminate environmental conditions such as brightness after cathode shock reinforcement so that illumination level acts as an acquired or secondary reinforcer . Essentially, this single celled organism is able to survive because it can anticipate the consequences of its environment that could determine its biological survivability. "
[Show abstract][Hide abstract] ABSTRACT: Background: Fatigue is a common term used to describe feelings of tiredness along
with observations of reduced physical effort in both health and disease. The study of
fatigue has centered mainly on understanding its putative causes. Recently (1990s),
fatigue has been researched with an expanded view encompassing its potential
origins and purposes in human physiology. Purpose: This review will explore
and consider different fatigue models which could assist in the evolving
understanding of this human condition. Methods: In this narrative review,
Medline and Google Scholar were initially utilized to identify studies and texts
documenting the developing understanding of fatigue. Following this, key words
were used to locate investigations describing reactions to external stimuli in basic
and complex organisms. The term anticipatory regulation was entered to locate
studies which evaluated this construct in both health and disease. Results: This
review shifts the focus of the fatigue paradigm from the catastrophe model,
which emphasizes peripheral energy supply and demand, to the anticipatory
regulation model, which focuses on a central regulatory process that anticipates
energy demands and makes adjustments to accommodate future demand. The
potential for this model to be used to explain the fatigue process in both health
and disease is also discussed with respect to specific pathologies. Conclusion:
There is now a body of evidence indicating that fatigue may represent a process
of anticipatory regulation for maintaining homeostasis.
"In Aplysia californica an aversive procedure in which a tactile stimulus is paired with a shock (Carew, Walters, & Kandel, 1981; Colwill, Absher, & Roberts, 1988) and an appetitive discriminative conditioning procedure have been used to study extinction (Colwill, Goodrum, & Martin, 1997). In Paramecium caudatum extinction has been tested in aversive Pavlovian procedures in which vibrations (Hennessey, Rucker, & McDiarmid, 1979) and light or dark areas (Armus, Montgomery, & Gurney, 2006 "
[Show abstract][Hide abstract] ABSTRACT: Extinction and its related phenomena are central to the study and development of associative learning theory. For a better understanding of the processes involved in extinction, it is important to know how general these phenomena are in different species. Extensive evidence of extinction in invertebrate species would be necessary in order to test the generality of its current theoretical and physiological accounts. We carried out three sets of experiments using terrestrial snails Helix aspersa. The repeated nonreinforced presentation of the conditioned stimulus (CS) resulted in a decrease in responding (extinction); the introduction of a delay between the extinction of a CS and its test produced an increase in responding (spontaneous recovery); and re-exposure to the unconditioned stimulus after extinction also led to an increase in responding (reinstatement). The results are discussed in relation to current interference theories of extinction.
"Another area of obscurity concerns the appropriate number of pairings in the acquisition phase to obtain a conditioned response. Along with a strong tradition of effective aversive taste conditioning  and in vivo immune conditioning , and in line with some prior work on unicellular organisms , we used only one pairing between the CS and the UCS. Another limitation is that habituation was tested in a group of cells that were simultaneously exposed to streptomycin. "
[Show abstract][Hide abstract] ABSTRACT: Recent advances in cell biology and gene regulation suggest mechanisms whereby associative learning could be performed by single cells. Therefore, we explored a model of classical conditioning in human macrophages in vitro. In macrophage cultures, bacterial lipopolysaccharide (LPS; unconditioned stimulus) was paired once with streptomycin (conditioned stimulus). Secretion of interleukin-6 (IL-6) was used as response measure. At evocation, conditioning was not observed. Levels of IL-6 were higher only in those cultures that had been exposed to LPS in the learning phase (p's < .05), regardless whether they received the conditioned stimulus or not at evocation.
However, habituation was evident, with a 62% loss of the IL-6 response after three LPS presentations (p < .001). If further experiments confirm that simple learning can occur in immune cells, this may have bearings not only on immune regulation, but also on the brain response to molecular signals detected in the periphery. Importantly, whether capacities for simple learning in single cells extend beyond habituation, and how this would be demonstrated, remain open questions.
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