Frontier: Ultrasound May Throw Neurons Off Course

by Elizabeth Norton Lasley

September, 2006

Few parents forget the first glimpse of their unborn baby’s face emerging from the grayish-black swirls of a sonogram. But new research cautions that ultrasound should be used for medical purposes only, not as a source of early baby pictures.

Reporting Aug. 22 in Proceedings of the National Academy of Sciences, Pasko Rakic of Yale University Medical school and colleagues found that in unborn mice exposed to ultrasound for long periods, a few developing neurons were derailed.

About half of the 335 fetuses studied underwent ultrasound scans for periods ranging from 5 to 420 minutes. After durations of longer than 30 minutes, a small number of neurons failed to reach their proper positions in the cortex, the outer covering of the brain and the seat of “higher” thought processes such as reason and analysis in humans.

The effect of this slight disruption remains unknown; the investigators are now conducting a follow-up study to examine effects on the animals’ behavior. “Even in the normal brain, not every cell is perfect,” Rakic notes.

The authors emphasize that in the much larger human brain, neurons migrate to their destinations over a much longer period—about 20 weeks, compared with less than one week in the mouse. To investigate possible parallels to humans, the team is conducting a similar study in primates.

“Until we have more information, our results support the FDA’s guidelines that ultrasound should be used only when medically necessary,” Rakic says.