Abstract
A simple step-down passive avoidance task was used to evaluate the perceptual awareness of a fearful situation in 15 normal cats and in animals with extensive lesions of the caudate nuclei or the frontal cortices. The lesions were made both in kittens and in adults but all animals were tested as adults. On each of 2 days the animal was twice placed on a platform and the latency to step-down was measured. After trial 2 of day 2 the animal received a 10-s unescapable shock. Single step-down retention trials were carried out at 24- and 48-h and 1-week after the one-trial training. There was a significant conditioning effect for all groups. There were significant group differences only on trial 1 of day 1 where the adult acaudates stepped down significantly slower than both the intact cats and the kitten-operated acaudates and on the 1-week retention-extinction trial where the same animals stepped down faster than the other groups. For the adult acaudates there was a significant inverse correlation between lesion size and the step-down latency for both trials of the 1st preshock day and for the trial immediately preceding shock. For the kitten acaudates no significant relationships were found between any of the parameters and the lesion magnitude. These data show that (i) animals with total removal of the caudate nucleus or the frontal cortex learned one-trial passive avoidance as readily as sham-operated and intact cats; (ii) adult acaudate cats were distinguishable from the other groups only by slower step-downs on the first habituation trial prior to shock, and more rapid extinction than either kitten acaudates or other control animals. We conclude that animals with extensive lesions of the caudate nuclei or frontal cortices are capable of avoiding an electric footshock. There are subtle changes in that avoidance behavior which may be attributed to the peculiarities in reactivity and activity previously described in acaudate animals.
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