Behavior Genetics

, Volume 3, Issue 2, pp 155–162 | Cite as

Genetic differences in susceptibility of rats to the immobility reflex (“Animal hypnosis”)

  • C. P. McGraw
  • W. R. Klemm


Several lines of evidence suggested that genetic factors influenced immobility reflex (IR) behavior, known commonly as “animal hypnosis,” a relatively unresponsive state of reversible immobility. Genetic influence was tested by comparing the susceptibility of two well-established strains of rats (Tryon) that had been developed for “maze brightness” (TMB) and “maze dullness” (TMD). The spontaneous durations of IR in TMB rats averaged approximately double those of TMD rats, and the time required to induce the state in TMB rats was significantly shorter. Correlated with the high IR susceptibility of the TMB rats was a pronounced lack of exploration in a novel environment. As another test of the hypothesis, selective inbreeding of Wistar rats led to the development of two strains, one highly susceptible and the other relatively insusceptible in the third and fourth generations. Testing revealed statistically significant differences between the two strains in terms of average duration of IR, average induction time, the percentage of susceptibility, the percentage which met the criteria for a high degree of susceptibility, and the percentage in each strain which were insusceptible.


Genetic Factor Genetic Difference Average Duration Genetic Influence Fourth Generation 
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Copyright information

© Plenum Publishing Corporation 1973

Authors and Affiliations

  • C. P. McGraw
    • 1
  • W. R. Klemm
    • 2
  1. 1.Department of NeurosurgeryUniversity of Texas Medical BranchGalveston
  2. 2.Department of BiologyTexas A&M UniversityCollege Station

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