Planarians in the Psychology Classroom

Planarians in the Psychology Classroom: Habituation and Instrumental Conditioning Demonstrations.

Charles I. Abramson, Deborah E. Kirkpatrick, Nathan Bollinger, Rihaneh Odde and Shannon Lambert

Oklahoma State University

Scheduled to appear in: In L. Benjamin, B. Nodine, R. Ernst, C. Blair-Broeker (Eds.). Activities handbook for the teaching of psychology, Volume 4. Washington, DC: American Psychological Association.


This paper describes two low cost demonstrations using planarians. With a plastic cheese cutting board and an airpuff from a 20 cc syringe, it is possible to demonstrate principles of habituation (and sensitization) including spontaneous recovery and influence of interstimulus interval. The same apparatus can be used to demonstrate principles of instrumental conditioning. In addition to the demonstrations, a suggested reading list is provided to enable an instructor to acquire background information on planarians and formulate ideas to modify the demonstrations.


Planarians as subjects for psychological demonstrations offer many advantages over more traditional vertebrate animals for laboratory course work and independent study. First they are inexpensive to procure and maintain. Second, planarians can be trained in a variety of mazes, runways and conditioning "troughs" that cost dollars rather than hundreds of dollars. Third, planarians can be used to demonstrate principles of the comparative analysis of behavior, ethology, the biochemistry of learning, physiological psychology, and behavioral ecology. Fourth, the nervous system of planarians is well suited to explore questions about the underlying physiology of behavior and the transmission of learned information from one animal to another. Fifth, students can reenact some of the more controversial studies in the history of learning such as the transfer of information between animals and whether planarians can actually associate a neutral stimulus with a unconditioned stimulus.

In this exercise, students use planarians to learn about principles of habituation and instrumental conditioning.

Materials Needed

Each research team should have one planarian, one 20 cc plastic syringe (without needle), one stop watch, one data sheet, one conditioning tray, one small paint brush, and enough spring or pond water to fill the conditioning tray(s). The instructor should also have two containers: one to hold the stock colony and the other to place conditioned planarians. In addition, the instructor should have extra planarians to replace any that fail to respond.

Conditioning Tray. A plastic bar and cheese cutting board (manufactured by Arrow Plastics, Elk Grove, IL, part number 00711) makes an excellent low cost conditioning tray. The tray costs about two dollars and is available from most supermarkets. A .8 cm deep by 1.4 cm wide trough lies along the perimeter of the cutting board and serves as the conditioning trough. To prepare the trough use the syringe to fill the trough with 15 cc of spring water. Planarian pond water can also be used (available from Ward's Biology, Rochester, NY, part number 88 W 7010). This produces a depth of approximately 5 mm which is deep enough for the animal to swim yet still react to the airpuff. If the bar and cheese cutting board is not available a plastic butter dish or petri dish will substitute. To administer the habituating stimulus or punishment (e.g., the airpuff) a plastic 20 cc syringe, available at any drug store or biological supply house, is used.

Planarians. Planarians are easy to obtain and care for and are available from any number of biological supply houses such as Ward's (Web address: For the more adventurous, planarians can be captured in ponds, streams, lakes and rivers throughout the United States. When planarians are ordered commercially instructions for feeding and maintenance are included. Planarians can be housed in any container that can hold water. The most important factor in maintaining a good planarian culture is clean water. The water should be changed once a week and be chlorine free. A good time to change the water is after a feeding. Planarians are primarily carnivorous and show a preference for fresh liver, although they will eat frozen liver that has been defrosted. A weekly feeding is quite sufficient to maintain healthy planarians. When the experiment is completed the instructor can decide to keep a stock colony for future demonstrations. If this is not desirable the stock colony and conditioned colony can be donated to a biology/zoology department, high school, or Head Start program.

Data sheet. A data sheet suitable for both demonstrations is available in Handout 1. The data sheet contains room for student information, observations, and data.


Identification of contraction response. For habituation experiments the response to an airpuff is a pronounced contraction of the planarian away from the direction of the airpuff

Identification of a turning response. For instrumental conditioning the turning response consists of a contraction followed by an extension of the animal. Following several contractions and extensions the animal begins to turn away from the direction of the airpuff and swims in the opposite direction. For example, if the animal is swimming in a clockwise direction repeated presentations of an airpuff elicits a number of contractions and extensions. These behaviors are followed by the animal turning and swimming in a counterclockwise direction. In our demonstration the dependent variable of interest is the number of airpuffs required to make the animal swim in the opposite direction. As training progresses the number of airpuffs required to produce a turning response steadily declines.

Conducting the experiment: Habituation.

In our demonstration the time between airpuff presentations (i.e., interstimulus interval) is 60 seconds, the intensity of the airpuff is 20 cc of air, the duration is approximately 1 second (the time to depress the syringe), and the number of trials 50. Having selected the experimental parameters the conditioning trough is filled with water and a planarian is removed from the colony with a paint brush and gently placed in the conditioning trough. Following a 5 minute adaptation period the airpuff is administer by first pulling back on the plunger of the syringe until the plunger reaches the 20 cc mark.

Next, direct the tip of the syringe to the head of the planarian and depress the plunger. Upon contact with the airpuff, a planarian will typically contract to about one half of its length. After the syringe is depressed the experimenter must do two things. First, the timer is started to begin the interstimulus interval (e.g. the time between airpuffs) and second, the presence or absence of a contraction response is recorded on a data sheet. It is often convenient to record a "1" if the animal contracted and a "0" if it did not. If graph paper is placed underneath the conditioning trough the contraction response may be quantified and expressed as the number of boxes exposed. If the planarian does not contract, for example, no boxes will be exposed and a 0 will be entered on the data sheet. With repeated applications of the airpuff the number of contractions decrease. When the experiment is completed the planarian should be returned to a home tank reserved for conditioned animals.

The experimental procedure for demonstrating habituation does not contain control procedures. It may be desirable for some members of the class to perform baseline experiments to determine the base rate of contraction in the absence of airpuff. Students also find it informative to modify the procedure to include sensitization trials to rule out sensory adaptation and motor fatigue as alternative explanations for the decrease in contraction they will observe. One way to provide such stimulation is to gently touch the animal with one of the bristles from the paint brush. Alternatively, a small drop of water can be splashed near the animal using an eyedropper. The animal should contract to the introduction of the new stimulus and contract again when the airpuff is reintroduced. If class time permits, students will find it interesting to vary the intensity of the airpuff by increasing or decreasing the volume of air in the syringe. The duration of the airpuff can also be easily altered by varying the speed in which the plunger of the syringe is depressed.

Conducting the experiment: Instrumental conditioning.

In a second demonstration, principles of instrumental conditioning can be explored with the same airpuff and cutting board used in the habituation demonstration. When filled with water, the trough in the cutting board makes an excellent rectangular planarian runway. To demonstrate the influence of response-reinforcer relationships planarians are given a series of airpuffs until they turn in the opposite direction. As the training session continues the number of airpuffs required to elicit turning behavior decreases.

In our demonstration the intensity of the airpuff is 20 cc of air, the duration of the airpuff is as short as possible (1 second or less), the intertrial interval is fixed at 1 minute, and the number of trials needed to conclude the experiment is 60. When the parameters of the experiment are decided the planarian is gently removed from its home container (with the paint brush) and given a 5 minute adaptation period.

When the animal is placed in the trough it will begin to move in one direction (e.g., clockwise or counterclockwise). Following the five minute adaptation period the experimenter will try and reverse this movement by giving the planarian a series of airpuffs directed to its head. When the planarian changes direction the stop watch is depressed to time the next intertrial interval and the number of airpuffs is recorded on the data sheet provided in Handout 1. Typically it will take 12 to 20 airpuffs before the animal changes direction. This will soon decrease to about 4-5. When the experiment is completed the subject is returned to a home container reserved for conditioned animals

As in the habituation experiment, students enjoy creating there own experimental designs. Some of the more common variations include manipulating the intensity of the airpuff, presenting the airpuff on a partial schedule of reward, delaying the time between the response and presentation of the airpuff, no longer present the airpuff following a turn (extinction), varying the intertrial interval, pretreating the animal with drugs such as caffeine, and investigating whether instrumental behavior survives regeneration.

Occasionally a student may encounter an unresponsive planarian. Therefore, whenever possible extra planarians should be brought to the class to replace those not contracting to the airpuff or, once contracted, do not re-extend. Such behavior is likely if the animals are dropping their tails, are overstimulated, or come from a polluted environment. If such behavior is observed the animals should be immediately removed from the conditioning chamber and gently returned to their home container.


The advantage of the demonstrations reported here are their extremely low cost and versatility. Moreover, students enjoy the hands-on approach. An entire research station containing a planarian and apparatus will cost under $6.00. In a small class each student can condition his or her own planarian. If the demonstration is presented to a large lecture class, the instructor can divided students into research teams where one member of the team, for example, presents the stimuli and the other member records data. An effective alternative to creating research teams is to place the apparatus on top of an overhead projector so the entire class can view the performance of a single animal.

Although not required, our experience suggests that students enjoy the planarian demonstrations more if they are integrated into a component on learning and memory. We also recommend that the component include information on the natural history and biology of these interesting organisms. Students also enjoy hearing about the unique place planarian learning holds in the history of psychology (Rilling, 1996).

The use of planarians to demonstrate principles of nonassociative and associative learning is also useful in generating classroom discussion about the importance of learning. Points for discussion include the usefulness of cognitive explanations of behavior, what are suitable control groups, what is a suitable statistical analysis, and what is the biological significance of conditioning.

Writing component

One of the strengths of this exercise is that it can be easily incorporated into an APA writing assignment. Students will formulate an hypothesis, conduct the literature review, design and carryout the experiment, analyze, graph, and discuss the results. An alternative writing assignment is to have students conduct a literature review with the goal of comparing their planarian results with those obtained with other species (Abramson, 1986, 1990, 1994; Abramson, Onstott, Edwards, & Bowe, 1996; Sheiman & Tiras, 1996). Students can also be asked to provide written answers to the discussion questions mentioned above and to create a poster presentation based on their library and classroom research.


Abramson, C.I. (1986). Invertebrates in the classroom. Teaching of Psychology, 13, 24-29.

Abramson, C.I. (1990). Invertebrate Learning: A Laboratory Manual and Source Book. Washington, DC: American Psychological Association.

Abramson, C. I. (1994). A primer of invertebrate learning: The behavioral perspective. Washington, DC: American Psychological Association.

Abramson, C.I., Onstott, T., Edwards, S., & Bowe, K. (1996). Classical-conditioning demonstrations for elementary and advanced courses. Teaching of Psychology, 23, 26-30.

Rilling, M. (1996). James McConnell's forgotten 1960s quest for planarian learning: A biochemical engram, and celebrity. American Psychologist, 51, 589-598.

Sheiman, I. M, & Tiras, K. L. (1996). Memory and morphogenesis in planaria and beetle. In C. I. Abramson, Z. P. Shuranova, & Y . M. Burmistrov (Eds.), Russian contributions to invertebrate behavior (pp. 43-76). Westport, CT: Praeger.

Suggested Background Reading

The material in this reading list was carefully selected to provide an instructor or interested student with information on various aspects of using planarians in the classroom. The material can be used to create a reading list on a specific topic or range of topics, offer tips and insights into various aspects of planarian behavior, stimulate classroom discussion and provide ideas for future student projects and instructor demonstrations.

Other classroom demonstrations using planarians.

Abramson, C.I. (1990). Invertebrate learning: A laboratory manual and source book. Washington, DC: American Psychological Association.

Katz, A. N. (1978). Inexpensive animal learning exercises for huge introductory laboratory

classes. Teaching of Psychology, 5, 91-93.

McConnell, J. V. (1967). A manual of psychological experiments on planarians (2nd ed.). Ann Arbor, MI: Journal of Biological Psychology.

Owren, M. J., & Scheuneman, D. L. (1993). An inexpensive habituation and sensitization learning laboratory exercise using planarians. Teaching of Psychology, 20, 226-228.

Review articles.

Corning, W. C., & Kelly, S. (1973). Platyhelminthes: The turbellarians. In W. C. Corning, J. A. Dyal, & A. O. D. Willows (Eds.). Invertebrate learning: Protozoans through annelids Vol. 1 (pp. 171-224). New York: Plenum Press.

Corning, W. C., & Ratner, S. C. (1967) (Eds.). Chemistry of learning. New York: Plenum.

Corning, W. C., & Riccio, D. (1970). The planarian controversy. In W. Byrne (Ed.), Molecular approaches to learning and memory (pp. 107-150). New York: Academic Press.

McConnell, J. V., & Shelby, J. M. (1970). Memory transfer experiments in invertebrates. In G. Unger (Ed.). Molecular mechanisms in memory and learning (pp. 71-101). New York: Plenum Press.

Sarnat, H. B., & Netsky, M. G. (1985). The brain of the planarian as the ancestor of the human brain. Canadian Journal of Neurological Sciences, 12, 296-302.

Sheiman, I. M, & Tiras, K. L. (1996). Memory and morphogenesis in planaria and beetle. In C. I.

Abramson, Z. P. Shuranova, & Y . M. Burmistrov (Eds.), Russian contributions to invertebrate behavior (pp. 43-76). Westport, CT: Praeger.

Habituation and sensitization experiments.

Westerman, R. A. (1963a). Somatic inheritance of habituation to light in planarians. Science, 140, 676-677.

Westerman, R. A. (1963b). A study of habituation of responses to light in the planarian Dugesia dorotocephala. Worm Runner's Digest, 5, 6-11.

Classical conditioning experiments.

Crawford, F. T. (1967). Behavioral modification of planarians. In W. C. Corning & S. C. Ratner (Eds.), Chemistry of learning (pp. 234-250). New York: Plenum Press.

Jacobson, A. L., Fried, C., & Horowitz, S. D. (1967). Classical conditioning, pseudo-conditioning, or sensitization in the planarian. Journal of Comparative and Physiological Psychology, 64, 73-79.

McConnell, J. V. (1962). Memory transfer through cannibalism in planarians. Journal of Neuropsychiatry, 3, 42-48.

McConnell, J. V., Jacobson, A. L., & Kimble, D. P. (1959). The effects of regeneration upon retention of a conditioned response in the planarian. Journal of Comparative and Physiological Psychology, 52, 1-5.

Thompson, R., & McConnell, J. V. (1955). Classical conditioning in the planarian, Dugesia dorotocephala. Journal of Comparative and Physiological Psychology, 48, 65-68.

Vattano, F. J., & Hullett, J. H. (1964). Learning in planarians as a function of interstimulus interval. Psychonomic Science, 1, 331-332.

Instrumental/operant conditioning experiments.

Best, J. B. (1965). Behavior of planaria in instrumental learning paradigms. Animal Behaviour, 13, Supplement 1, 69-75.

Corning, W. C. (1964). Evidence of right-left discrimination in planarians. Journal of Psychology, 58, 131-139.

Crawford, F. T., & Skeen, L. C. (1967). Operant responding in the planarian: A replication study. Psychological Reports, 20, 1023-1027.

Humpheries, B., & McConnell, J. V. (1964). Factors affecting maze learning in planarians. Worm Runner's Digest, 6, 52-59.

Krebs, E. K. (1975). Factors in conditioning and orientation of planarians: Learning in a polar field. Journal of Biological Psychology, 17, 21-23.

Lee, R. M. (1963). Conditioning of a free operant response in planaria. Science, 139, 1048-1049.

Wells, P. H. (1967). Training flatworms in a Van Oye maze. In W. C. Corning & S. C. Ratner (Eds.), Chemistry of learning (pp. 251-254). New York: Plenum.

Influence of pollutants and drugs on behavior.

Bonner, J. C., & Wells, M. R. (1987). Comparative acute toxicity of DDT metabolites among American and European species of planarians. Comparative Biochemistry and Physiology (C): Comparative Pharmacology and Toxicology, 87, 437-438.

Congiu, A. M., Casu, S., & Ugazio, G. (1989). Toxicity of selenium and mercury on the planarian Dugesia gonocephala. Research Communications in Chemical Pathology and Pharmacology, 66, 87-96.

Johnson, L. R., Davenport, R., Balbach, H., & Schaeffer, D. J. (1994). Phototoxicology: 3. Comparative toxicity of trinitrototoluene and aminodinitrotoluenes to Daphnia magna, Dugesia dorotocephala, and sheep erythrocytes. Ecotoxicology and Environmental Safety, 27, 34-49.

Kessler, C. C. (1973). The effect of magnesium pemoline on learning in the planarian. Journal of Biological Psychology, 15, 31-33.

Comparative/ethological investigations.

Dolci Palma, I. A. (1987). The hunting and eating of prey by planarians of the species Dugesia tigrina kept in the laboratory. Ciencia e Cultura, 39, 557-560.

Loh, P. Y., Yap, H. H., Chong, N. L., Ho, S. C. (1992). Laboratory studies on the predatory activity of a turbellarian, Dugesia sp. (Penang) on Aedes aegypti, Anopheles maculatus, Culex quinquefasciatus and Mansonia uniformis. Mosquito Borne Diseases Bulletin, 9, 55-59.

Mason, P. R. (1973). Size and other factors determining planarian behaviour. Journal of Biological Psychology, 15, 8-13.

Mason, P. R. (1975). Chemo-klino-kinesis in planarian food location. Animal Behaviour, 23, 460-469.

Nixon, S. E. (1974). Some behavioral observations on a cave dwelling planarian. Journal of Biological Psychology, 16, 32-33.

Peters, A., Streng, A., & Michiels, N. K. (1996). Mating behaviour in a hermaphroditic flatworm with reciprocal insemination: Do they assess their mates during copulation? Ethology, 102, 236-251.

Reynierse, J. H., & Gleason, K. (1974). Determinants of planarian aggregation behavior. Animal Learning and Behavior, 3, 343-346.

Rivera, V. R., & Perich, M. J. (1994). Effects of water quality on survival and reproduction of four species of planaria (turbellaria: tricladida). Invertebrate Reproduction and Development, 25, 1-7.

Zoological/natural history information.

Barnes, R. D. (1974). Invertebrate zoology (3rd edition). Philadelphia: W. B. Saunders.

Pearse, V., Pearse, J., Buschbaum, M., & Buschbaum, R. (1987). Living invertebrates. Pacific Grove, CA: The Boxwood Press.


Name: _____________________ Experiment: Habituation, Instrumental, Other

Date: _____________________ Time: _______________ Subject #:_________

Number of trials: ______________ ISI/ITI: _______________ Subject Size:_______

Stimulus intensity:______________ Stimulus duration:________ Other:____________






























































A sample experiment

The equipment that will be needed:
  • Dish
  • Small brush
  • Syringe
  • Vial
  • Planarian
The planarians are kept in a recycled fish tank. They are fed liver.
Put your planarian into a container to transfer it to the conditioning plate. To get it out, use the brush.
With a puff of air, it will contract.
After a few puffs, it should stop contracting. It is now habituated.

Dr. Charles I. Abramson
Department of Psychology
116 N. Murray
Stillwater, Ok 74078-3064
(405) 744-7492
via E-Mail:

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