THE EFFECTS OF TRAINING IN CRAWLING ON THE MOTOR AND MENTAL DEVELOPMENT OF INFANTS

LAGERSPETZ, K., NYGÅHD, M. & STRANDVIK, C. The effects of training in crawling on the motor and mental development of infants. Scand. J. Psychol. , 1971 12, 192–197.–Eleven infants under the age of 1 year were trained in creeping for 15 minutes daily for 3 weeks, while 11 children, who served as controls, spent the corresponding times with the experimenters without training. The experimental group learned to creep significantly earlier, and transfer effects on other locomotor development were observed. Even effects on factors other than motor developmental were obtained. A training experiment with a pair of monozygotic twins is also reported.     

EXPERIMENTS CONCERNING THE TRANSFER OFA LEARNED RESPONSE AND ACTIVITY LEVEL BY BRAIN HOMOGENATES

L agerspetz , K. M. J., R aitis , P., T irri , R. & L agerspetz , K. Y. H. Experiments concerning the transfer of a learned response and activity level by brain homogenates. Scand.J. Psychol ., 1968, 9, 225–229,— The learning of a conditioned avoidance response caused an increase in the open-field activity of male albino mice. Pseudo-conditioning had an opposite effect. The transfer of brain homogenate from the trained animals did not facilitate the acquisition of the avoidance response by the recipient animals. Differences in the open-field activity were not transmitted with the brain homogenates. However, the constancy of the open-field activity scores was decreased by the homogenate injection, and also by severe electric shocks.     

GENETIC AND SOCIAL CAUSES OF AGGRESSIVE BEHAVIOUR IN MICE

L agerspetz , K irsti . Genetic and social causes of aggressive behaviour in mice. Scand. J. Psychol ., 1961, 2 , 167—-173.—Significant differences in the aggressiveness of mice selected for aggressiveness and non-aggressiveness have been found to occur in the 2nd and 3rd generation of selective breeding. In S _a, motor activity scores were significantly higher in mice of the aggressive than of the non-aggressive strain. Defecation and ambulation scores obtained both in a standardized open-field test and in connection with the aggression measurements showed that the S₃ descendants of the aggressive mice were emotionally less reactive than the members of the 3rd non-aggressive generation. Defeats tend to decrease, victories to increase the level of aggressiveness in mice, but the aggression scores tend to return to the original level after the termination of the experiments.     

The decline of aggressiveness in male mice during group caging as determined by punishment delivered by the cage mates

Group-housed rodents are generally less aggressive than isolated counterparts. The present study examined the role of defeat by cage mates as a reason for this decline in aggressiveness. In Experiment I, highly aggressive isolated male mice were introduced into aggressive or nonaggressive resident groups. The intruder's level of aggressiveness directed toward a group-housed standard opponent declined more rapidly after daily exposure to the aggressive than to the nonaggressive groups. Intruders in the aggressive groups received more attacks from their cage mates, and delivered fewer attacks to them than did the intruders in the nonaggressive groups. In Experiment II, the intruders lived for seven days in small wire net cages in the middle of the group cages. Their level of aggressiveness toward standard opponents decreased little during the preexposure but after being put freely into the groups, their aggressiveness declined to a minimal level within a day. Experiment III showed that when the wire net protection in the middle of the cage was installed after the group caging experience, the aggressiveness of the intruders did not return to the isolation level as effectively as it did in isolation. This is explained by the aggression-inhibiting content that the cues from the cage mates have acquired during group caging. The decline of aggressiveness in male mice during group caging is determined by punishment delivered by the cage mates.     

NEUROCHEMICAL AND ENDOCRINOLOGICAL STUDIES OF MICE SELECTIVELY BRED FOR AGGRESSIVENESS

L agerspetz , K. Y. H., T irri , R. & L agerspetz , K. M. J. Neurochemical and endocrinological studies of mice selectively bred for aggressiveness. Scand.J. Psychol ., 1968, g, 157–160.—Several neurochemical and endocrinological variables were studied in male albino mice from two strains, selectively bred for aggressiveness and non-aggressiveness. Differences were found in the weight and the serotonin content of the forebrain, in the catecholamine contents of the brain stem and of the adrenal gland as well as in the weight of the testis. The results indicate that mice selectively bred for aggressiveness show physiological signs of higher orthosympathetic activity than the mice selectively bred for non-aggressiveness.     

THE EFFECTS OF SOCIALLY-INDUCED AGGRESSIVENESS OR NONAGGRESSIVENESS ON THE SEXUAL BEHAVIOUR OF INEXPERIENCED MALE MICE

H autojävi , S. & L agerspetz , K. The effects of socially-induced aggressiveness or nonaggressiveness on the sexual behaviour of inexperienced male mice. Scand. J. Psychol ., 1968, 9, 45–49.—High aggressiveness induced by repeated victories over another mouse was found to decrease sexual behaviour of male albino mice. Nonaggressiveness induced by defeats in fights did not affect the level of sexual activity as compared with that of the control animals.