The other position—taken by Anderson and others—is that developmental attainments are of no real value in predicting the level of intelligence but are measures of completely different functions. Illingworth and most clinicians, including the authors, have taken an intermediate position, that the developmental scale in early life is a useful source of information, but it must be combined with a full clinical assessment. When this is done, the clinician has a reasonably certain means of detecting delays in cognitive development and other forms of neurologic impairment.
The trajectory of rapid growth and maturation continues in late childhood and adolescence, although at a slower pace than before. Motor skills attain their maximal precision in the performances of athletes, artists, and musicians, whose peak development is at maturity (age 18 to 21 years). Intelligence and the capacity for reflective thought and the manipulation of mathematical symbols become possible for most individuals only in adolescence and later. Emotional control, precarious in the school age and all through adolescence, stabilizes in adulthood. We tend to think of all these phenomena as being achieved through the stresses of human relations, which are conditioned and habituated by the powerful influences of social approval. In this extensive and pervasive interaction between the individual and the environment, which is the preoccupation of the child psychiatrist, it is well to remember that the processes of extrinsic and intrinsic organization can be separated only for the purpose of analytic discussion. There is always interdependence between them.
As indicated earlier and in Table 27-4, the wide variety and seemingly random movements displayed by the healthy neonate are from birth, and certainly within days, firmly organized into reflexive-instinctual patterns called automatisms. The most testable of the automatisms are blinking in response to light, tonic deviation of the eyes in response to labyrinthine stimulation (turning of the head), prehensile and sucking movements of the lips in response to labial contact, swallowing, avoidance movements of the head and neck, startle reaction (Moro response, see further on) in response to loud noise or dropping of the head into an extended position, grasp reflexes, and support, stepping, and placing movements. This repertoire of movements, as mentioned earlier, depends on reflexes organized mainly at the spinal and brainstem levels. Only the placing reactions, ocular fixation, and following movements (the latter are established by the third month) are thought to depend on emerging cortical connections, but even this is debatable. In the neonatal period, when little of the cerebrum has begun to function, extensive cerebral lesions may cause little derangement of motor function and may pass unnoticed unless special methods of examination—sensory evoked potentials, electroencephalography (EEG), CT, and MRI—are used. Of clinically testable neurologic phenomena in the neonatal period, disturbances of ocular movement, seizures, tremulousness of the arms, impaired arousal reactions and muscular tone, all of which relate essentially to upper brainstem and diencephalic mechanisms, provide the most reliable clues to the presence of neurologic disease. Prechtl and Beintema have affirmed the importance of disturbances of these neurologic functions at this early age as predictors of delayed development.