In the 1920's, researchers began investigating whether a fetus in the womb could develop short-term memory. Experimenting with pregnant women, they used the sound of a car horn to determine that over time, a fetus will remember the sound and stop reacting to it. The technical term is habituation, which is not considered memory in the traditional sense. However, new research suggests that a fetus might actually be capable of developing more long-term memories.

In a study of 100 pregnant women, researchers used ultrasound to watch fetal movements while "vibroacoustic" sounds were played. ("Vibroacoustics" is the process of hearing sound vibrations through the body.) Like the car horn experiment, they discovered that when the sound was repeated, the fetus eventually stopped responding to it. But by waiting longer intervals between sounds, they found that fetuses as young as 30 weeks could remember the sound for 10 minutes. At 34 weeks, a fetus may remember the sound for as long as 4 weeks.

"What is critically important to recognize, however, is that these memories are not conscious or introspective voluntary memories they way an older child or adult thinks about past experiences," says Mark Strauss, autism researcher and associate professor at the University of Pittsburgh. "They are very different and, indeed, involve lower areas of the brain that are very different from high-level brain area."Despite the differences, the research has the potential to change the way we think about the impact of stimulus on very young children, including those still in the womb.

"It's interesting to say that babies have some memory, some intake of things, even if they're born premature. There's a lot of movement towards making intensive care units friendlier, controlling noise for example, for premature babies," said Dr. Paul Graham Fisher, a professor of neurology at Stanford University.

For parents-to-be, this research also suggests that laying a speaker on your belly and playing Mozart for your unborn child isn't as silly as they may have believed. In addition to soothing both the mom and the baby with classical music, they might also be making beautiful memories.