Pavlovian Lever-Directed Activity in Rats with Microcephaly Due to Gamma Irradiation
Rats with microcephaly induced by prenatal exposure to ionizing irradiation have been reported to be capable of good performance on tests of associative learning despite being impaired on tests of cognitive learning ability. As a measure of associative learning, six adult rats, prenatally exposed to a single dose of 150rad of gamma irradiation on the sixteenth day of gestation, were compared with six sham-irradiated rats in a Pavlovian autoshaping sitation that involved testing the animals in conditioning chambers in which there were two perspex levers which could be illuminated from behind. The illumination of one lever (CS+) was predictive of food reinforcement, while the illumination of the other lever (CSo) was not. The delivery of food was not contingent upon a response being made by the animal. Twenty illuminations of each lever occurred per session. Fifteen autoshaping sessions were given followed by ten in which the predictive significance of the levers was reversed for the animals. Despite the overall reduction in brain size (mass, volume and encephalization quotient) and varying degrees of internal disruption seen in the prenatally irradiated rats’ brains (for example, rudimentary corpus callosum, ectopic tissue masses, thin cortical mantle, dilation of ventricles) there were no differences during the initial fifteen autoshaping sessions in the total number of contacts or presses made by the two groups to the CS+ when it was illuminated.
KeywordsGamma Irradiation Associative Learning Brain Size Prenatal Exposure Conditioning Chamber
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