Some paradoxical effects of bilateral lesions in the frontal cortex in rats

Abstract

Rats with bilateral lesions of the frontal cortex were trained to discriminate between patterns of horizontal and vertical black and white stripes. The preference established on the initial discrimination learning was then reversed a total of eight times, e.g. if vertical stripes were positive on Reversal R 0, horizontal stripes were positive on Reversal R 1, vertical stripes on Reversal R 2, and so on. On the initial discrimination and each of the eight successive reversals, the frontal animals required fewer trials to reach criterion than a mock operated control group. Detailed analyses of the results enabled a comparison to be made between several possible competing explanations of the observed differences. It is concluded that the explanation which best fits the present results and those of other relevant studies is that the effect of frontal lesions is to reduce the anxiety and frustration which are otherwise generated by a task in which every time the animal reaches criterion with one set of stimuli, the signs of the stimuli are immediately reversed.