[Formation and development of motor-defense conditioned reflexes in rats of different ages]

The analysis of the reflex conditioned activity of rats at various age groups showed that there were differences in it. There was a considerable strength of the excitatory process in young rats, aged one and a half months. The positive reflexes to sound and light stimuli were formed compatively quickly (on the average after 8,6 and 4,8 combinations of the conditioned stimulus with the unconditioned stimulus) in comparison with the animals of mature age (respectively 16,5 and 8 combinations). In the old rats the author observed a lowering of the strength of the excitatory process and slower formation and stabilization of the positive conditioned reflexes. A gradual formation of the inhibitory function occurs during the process of ontogenetic development and this finds an expression in the unpossibility for the fromation of differentiation in young animals and the presence of such in 10-month old rats. The level of the differentiations in these animals reached 60,1% and 76,9%. The latent period changed with the advancement of age. In adult animals there was some shortenint ofthelatent period in comparison with the young animals although the difference was statistically insignificant. There was an increase of the absolute values of the latent period again after the occurrence of the old age (5,2'' and 4,52''). The indicated peculiarities in the formation and course of the conditioned reflexes probably were connected with various degree in the fluctuations of the strength of the exitiatory and inhibitory processes in the central nervous system during ontogenesis.