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TASTE ADVERSION IN DEAD RATS:
LEARNING OR MOTIVATIONAL DEFICIT?

AUTHOR: Robert Deutsch
Department of Psychology
York University
Downsview, Ontario, Canada

Previous research, demonstrating that rats poisoned while dead will not thereafter drink a previously preferred solution, was replicated. The present research demonstrates that the suppression of intake indeed represents a learned adversion rather than a change in motivational level.

Kalat (1973) has reported that rats poisoned while dead will not thereafter drink a previously preferred saccharin solution. He has interpreted this finding as demonstrating taste-aversion learning in dead rats. While this interpretation has a certain intuitive appeal, his data do not exclude the possibility that the reported decrease in intake is due to a change in drive, i.e., that the change in behavior represents a change in performance (SER;) rather than learning (SHR) (see Hull, 1943). The present experiment provides an explicit test of the hypothesis that the reported taste-aversion phenomenon in dead rats represents a change in drive state.

METHOD

Subjects were 50 female native albino rats, 225-250g, kept in individual wire mesh cages. Purina Lab Chow was available ad lib; water was available for one hour per day.

On the conditioning day, all the rats were given access to 0.196 (Wt/V) saccharin solution, previously unfamiliar to the rats, for 30 minutes. This constituted the initial preference test to be compared with a post-poisoning preference test, with each rat serving as its own control. At the end of 30 minutes each rat was killed with an overdose of ether. An additional 30 minutes were allowed to elapse, allowing all the cells of the body to die. At the end of this period each rat was poisoned by an i.g. intubation of 1 ml/20g body weight of 0.15 M LiCl. The procedure up to here is identical to that followed by Kalat (19T3).

After poisoning, each rat was assigned to one of five groups. The groups differed on the variable of extent of water deprivation (i.e., drive) at the time of testing (see Table 1).

TABLE 1
Time between poisoning and test
Group 1 2 hours
Group 2 24 hours
Group 3 48 hours
Group 4 72 hours
Group 5 96 hours

After the appropriate delay, all rats were again offered the saccharin solution for the post-poisoning preference test.

RESULTS

Table 2 shows intakes in the 5 groups in the initial and in the post-poisoning preference tests.

TABLE 2
Mean lntake, Initial Test, ml. Mean Intake, post-poisoning, ml.
Group 1 14. 2 0
Group 2 13. 8 0
Group 3 14. 0 0
Group 4 14 .1 0
Group 5 13 .1 0

Analysis of Variance. Two-way analysis of variance showed a highly significant effort of poisoning (p<.0000000001), but no significant differences due to period of water deprivation, and no interaction between poisoning and deprivation.

DISCUSSION

Kalat (1973) has demonstrated that poisoning suppresses intake of a preferred saccharin solution even in dead rats. The present experiment evaluated the possibility that the reported decrease in intake represents a change in drive rather than learning. Since varying drive in the test situation had not effect on intake, it can no longer be argued that the reported effect is due to drive. Alsom since the range of deprivation periods used was from 2 to 96 hours, it cannot be argued that the range of deprivation conditions taste-aversion learning in dead rats points out the usefulness of this preparation, since, unlike much of human learning (see Patterson and Guillion, 1971), it is clearly intrinsically rather than extrinsically motivated.

REFERENCES

Hull, C. L. Principles of Behavior New York: Appleton-Century-Crofts, 1943.

Kalat, J.W.. Taste-aversion Learning in Dead Rats The Worm Runner's Digest 1973, 15, 59-60.

Patterson, G.R., & Gulliun, M. E. Living with children Champaign, Ill.: Research Press, 1971.

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