The idea that early experiences can have a profound influence on functioning dur­ ing a later developmental period has been a fundamental theme in developmental theories. More recent theories have expanded on this idea, suggesting that early experiences may actually be incorporated into the individual’s biology by altering neural processes. These altered neural substrates then influence the way the indi­ vidual meets new experiences (Boyce et al., 1998; Cicchetti & Tucker, 1994). No one doubts that exposure to substances in utero via maternal intake can alter be­ havioral development (for example, cigarette smoking, alcohol, and many other drugs are acknowledged to have deleterious effects on offspring). Researchers have long been interested in the idea that even experiences during the fetal peri­ od can influence later development (Carmichael, 1970; Kuo, 1976). In spite of this long-standing interest, the issue of whether environmental events experienced by the mother during gestation can alter behavior and the neural substrates of be­ havior in the offspring has received only limited research attention.