Effect of specific and non-specific stimuli on the visual and motor cortex of the rat

Abstract

Summary In order to study the possible simultaneous influences of light and darkness, and mobility and restraint on the visual and motor areas of the cortex, we have studied the visual and motor cortex of 4 groups of rats raised under the following conditions: (1) in normal light conditions and large cages; (2) in normal light conditions and cages small enough to restrain the movement of the animals; (3) in total darkness and large cages and (4) in total darkness and small cages. They were kept in these conditions from weaning until they were 90 days old. At this time they were killed and their brains stained following the rapid Golgi procedure. The spines along the apical shaft of the pyramidal neurons of layer V of the visual and motor cortex (a total of 20–25 cells/group) were counted. The results were processed in a PDP 11/40 computer. While darkness produced a decrease in the mean number of dendritic spines of only the visual cortex, restraining the animal produced a significant decrease in the mean number of spines in both cortices, motor and visual. Furthermore, the influence of restraining was found so strong on the visual cortex that it masked the effect of darkness. There was no significant difference between the mean number of spines per shaft of animals held restrained and in light, versus animals held restrained and in darkness. These results indicate that movement itself is very important for the correct development of dendritic spines in the visual cortex.