San Diego

The effect of ultrasound scans on brain development is to be investigated in a study on monkeys starting next month in the United States. The work has been prompted by unpublished research showing that ultrasound can disrupt the normal movement of cells through the brains of unborn mice.

The $3-million study, which is funded by the US National Institute of Neurological Disorders and Stroke in Bethesda, Maryland, will examine the effect of scans on the unborn offspring of around 50 rhesus macaque monkeys. Pasko Rakic and his colleagues at Yale University in Connecticut, will expose the monkeys to ultrasound at different times during pregnancy. Brain cells of interest will be tagged with a marker molecule before the scans, and the final position of the neurons will be assessed when the animals are killed after birth.

Rakic announced the study on 24 October at the annual meeting of the Washington-based Society for Neuroscience, held in San Diego. He will not reveal details of his preliminary mice study until the latest work has been published, but he says that the scans seem to interfere with the migration of neurons from the centre of the developing brain to the cortex — the outer layer of the brain that handles everything from movement to speech.

“The cells are slowed down and more spread out,” he says. “Some of them are not getting to their final destination.”

The movement of neurons in the developing fetus, on which Rakic did pioneering studies during the 1970s and 1980s, is known to be disrupted by certain viruses, genetic mutations and drugs taken during pregnancy. Studies have linked such disruption to a range of human conditions, including some forms of autism and learning difficulties.

Radiologists caution that more information is needed about the ultrasound dose used on the mice before any relevance to humans can be discussed. At high doses, for example, ultrasound causes a heating effect that damages tissue. “People have been studying the effect of ultrasound on development since the 1970s,” says William O'Brien, a specialist in bioacoustics at the University of Illinois at Urbana–Champaign. “We've not seen anything when levels equivalent to those allowed for humans are used.”