Control of hoarding activity in rats by the median cerebral cortex.

Abstract

An operative technique for applying lesions to the median surface of the cerebral cortex was developed which avoided excessive bleeding from the sagittal sinus. 15 rats in the "median group" received bilateral lesions along the median cortical surfaces and 8 rats in the "lateral group" received bilateral lesions along the dorsolateral cortical surfaces. The number of pellets collected by rats during 20 minute hoarding trials were detd. before and after the operations. The mean size of the lesions was 13.7% and 13.3% of the neocortex for the lateral and median groups, respectively. The mean hoarding scores for the former group were 35.8 pellets pre-operatively and 33.6 pellets post-operatively. Corresponding scores for the median group were 34.3 pellets and 8.65 pellets. A "deficit index" was computed for each rat in the median group. This index ranged between 0.38 and 1.00 with a mean of 0.73, and was related to the length of the median cortical lesions along the midline of the brain by a product-moment correlation coefficient of 0.874. Comparisons of the 2 groups of rats during post-operative trials showed no important differences on measures of day of onset of hoarding, daily latency, and speed of hoarding. It was concluded that the effect of small lesions of the median cortical surface was to greatly reduce the amount of hoarding, without influencing other measures of hoarding activity. This restricted cortical area therefore seems to control hoarding activity in the rat.