ABSTRACT
Habituation is a measure of the ability to inhibit responding and is a more mature
form of behavior than is persistent responding. We examined the developmental trend
in habituation of the fetal startle response to repeated vibroacoustic stimulation
in 90 normal human fetuses between 28 and 40 weeks of gestation. Fetal movement was
graded according to the nature of the behavioral response: general startle (3), fast
limb movement (2), slow rolling movement (1), and no movement (0). A significant developmental
difference (p <0.0004) in the rate of habituation was found, with response decrement occurring
faster in fetuses of more than 32 weeks of gestation. Furthermore, by dividing the
patients into three gestational age groups, it was determined that the greatest change
in the rate of habituation occurred between 28 and 32 weeks and 32 and 36 weeks. We
conclude that the rate of fetal habituation may be determined by the degree of maturation
of the neural circuitry governing this form of nonassociative learning.
