Images suggest childhood lead exposure linked to faulty brain wiring.

Brubaker, CJ, VJ Schmithorst, EN Haynes, KN Dietrich, JC Egelhoff, DM Lindquist, BP Lanphear and KM Cecil. 2009. Altered myelination and axonal integrity in adults with childhood lead exposure: a diffusion tensor imaging study. NeuroToxicology. doi:10.1016/j.neuro.2009.07.007.

Exposure to low to moderate levels of lead before birth and as a child can permanently change the brain's structure in a way that may alter if and how it transmits messages, a new study finds. The conclusions are based upon comparisons of  images of the brain's nerves and their protective coverings – collectively called white matter.

More differences in the nerve cells and the thickness of their coverings were found in adults who had higher lead exposure during development and as children. Some areas of the brain developed less robust nerve pathways and other parts had thicker or thinner coverings.

These changes in how the brain formed were not great enough to result in overt diseases and disorders that are typically associated with white matter damage – such as multiple sclerosis. However, the varied construction may play a role in the "recognized adverse neuropsychological outcomes associated with childhood lead exposure," say the paper's authors.

The new study is one of just a handful that have looked at the way lead alters brain development. The results fall in line with past studies and show that changes in the nervous systems of people who were exposed to lead as children are similar to changes initially described in laboratory experiments using nerve cells.

The effects of lead on the developing nervous system are well documented. Its long-lasting effects include abnormalities in cognitive or thinking processes, behavior and movement.

However, the ways that lead alters and damages the nervous system are not well understood.

To learn more about these processes, the researchers used magnetic resonance imaging (MRI) to look for changes in the white matter of the brain. The 91 participants – who ranged in age from 20 to 25 years old – were part of the Cincinnati Lead Study and had been followed since before birth for lead exposure.

White matter is akin to the highways of the brain where axons (the long part of nerve cells surrounded by myelin sheaths) carry electrical signals between different regions of the brain and the spinal cord. When white matter is damaged, diseases can occur.

In the study, many of the white matter regions of the brain had changes consistent with damage to the axons as well as to the myelin sheaths. Myelin consists of brain cells that wrap around axons to improve the transfer of information along the axons. These changes can result in the faulty transfer of information though the nervous system.

Greater white matter changes were seen in those who had larger exposure to lead as children. Those exposures – measured as blood lead levels – ranged from about 5 to 37 micrgrams per deciliter (ug/dl) of blood, with the majority falling between 5 and 10. The US Centers for Disease Control considers blood lead levels above 10 ug/dl elevated. However, many experts believe there is no "safe" level of lead exposure, especially during development and childhood.

The white matter in the brain forms while the child is still in the womb and finishes forming during the early years of life, which is when the brain is most sensitive to the effects of lead. The changes seen were present in young adults studied, showing the effects of childhood lead exposure are not something that will just get better with time.