NEURAL MATURATION AS EXEMPLIFIED IN THE CHANGING REACTIONS OF THE INFANT TO PIN PRICK

Abstract

In a series of studies (6, 7, 8, 9) of the early motor development of the infant it has been shown that alterations in overt behavior can be interpreted rationally as evidence of organization of the central nervous system. An analysis of sensory development in the infant, segregated from motor functioning, is precluded since a baby cannot report his sensory perceptions. However, changes in response to peripheral stimulation can be used to appraise maturational processes, or reorganization of sensori-motor mechanisms. In order to determine salient features of change in overt behavior a group of 75 infants were stimulated by pin prick (blunt sterile safetypin) at repeated intervals from birth to four years and their responses recorded either on motion picture film or by written protocols. A total of 2,008 observations were made, many of which consisted of stimulations in four different areas, these areas representing ma3or anatomical divisions, viz., the head, trunk, upper and lower extremities. Ten pin pricks were applied to each area. Without this summation-effect the reactions might have been less intense. Efforts to control (mechanically) the intensity of the stimulus were abandoned because the diffuse movements of the child often introduced tactile or other sensations. Since this study was concerned not with sensory thresholds, but with the development of overt response to cutaneous irritation, the less cumbersome technique was adopted. Of the total number of observations 648 were recorded on motion picture film, and 1,362 consisted of descriptive reports of observable behavior. In addition to the serial records over a period of years, daily observations were made upon four individual infants during the first 18 to 24 months of life. Two of these infants were identical twin boys; the other two were unrelated girls. Examination of these cinema and descriptive records revealed certain significant features of the sensori-motor aspect of the behavior which reflected reorganization of the neural mechanisms involved. Similarly, salient qualities in the cognitive and conative aspects of the behavior seemed to express advancing neural maturation. The analysis of sensorimotor aspects of the behavior was based primarily upon responses to the application of the stimulus to the skin, and the cognitive and conative aspects were based upon the responses of the infant to the stimulus, (i.e., the pin), in the visual field, or to the experimental conditions in general. The sensori-motor aspects of the activity were conveniently classified into four ma3or categories. There were also four significant phases in the cognitive and conative aspects of the behavior. However, changes in cognitive and conative aspects of the response did not necessarily parallel changes in sensori-motor functioning. These developmental phases can be better clarified by a detailed description of the criteria used in selecting the sequential stages of development.