The 1987 James A. F. Stevenson memorial lecture. The development of fetal behavioural patterns

The development of fetal behaviour is reviewed. Fetal cutaneous and muscle sensory receptors are developed by the time movements are first seen. Human infants certainly respond to painful stimuli at 28 weeks. There is no clear evidence that prenatal "stress," e.g., maternal exposure to random noise and bright lights, impairs fetal development in the rat, on the contrary. Fetal diurnal rhythms appear in man and sheep before the development of sleep states; they are dependent on maternal corticosteroids, but the fetal mechanism is uncertain. With the development of sleep states (in late gestation in man and sheep, postnatally in the rat), the complex central control of behaviour is gradually established, but wakefulness is still of low incidence. The location of the sleep cycle generator is uncertain; the results of experimental lesions of the brainstem in fetal lambs appear incompatible with studies in adult rats and cats.