Selection for high rates and low rates of avoidance conditioning in the rat

Abstract

This paper describes the results of the first five generations of selection for high and low rates of avoidance conditioning in the Wistar albino rat. The number of conditioned avoidance responses made in a shuttle-☐ during five daily sessions of 50 trials each, with light as the conditioned stimulus and shock as the unconditioned stimulus, steadily increased over the first four generations in the line selected for high rate of avoidance conditioning. Downward progress of selection was also marked in the strain selected for low rate of avoidance conditioning, but with wider fluctuations. Differences due to the sex of the animals and to the system of breeding (inbreeding versus outbreeding) were also initially observed in the Low Avoidance strain. The differences disappeared later, but the effect of inbreeding could not be investigated beyond the third generation because the inbred line became extinct. While no post-natal maternal effect was detected in a cross-fostering experiment, suggestive evidence of a prenatal effect was obtained by reciprocally crossing the selected strains.