During the study, reported in the journal Neurology, 112 smelter workers in New Brunswick, Canada, underwent several cognitive and motor speed tests and a measure of reading ability. The researchers calculated working lifetime lead exposure from historic blood lead levels obtained by the smelter.
The workers were then divided into groups with high cognitive reserve, defined as a reading level of 12th grade or higher, and low cognitive reserve, a reading level of 11th grade or lower.
"Even though the two groups had similar lead exposure, the cognitive effects of lead were 2.5 times greater in workers with low reading ability. In contrast, the effect of lead on motor speed was comparable in both groups as cognitive reserve does not apply to motor speed," said study author Dr. Margit L. Bleecker of the Center for Occupational and Environmental Neurology in Baltimore, and member of the American Academy of Neurology.
"This suggests that high cognitive reserve has a protective effect that allowed these workers to maintain their functioning, even though lead affected their nervous system as shown by its effect on their motor skills," the author added.
Dr. Bleecker further said that there are multiple theories on how cognitive reserve, or the brain's ability to maintain function in spite of damage, protects against insults to the organ.
"These include an increased concentration of cortical synapses in larger brains that provide more brain capacity, a greater ease of using alternative brain circuits, and the ability to process tasks more efficiently in current brain circuits," said Bleecker.