A de cline in incom e in young adulthood may lead to poorer cognitive ability in middle age. Income reductions are also linked to changes in brain structure that suggest premature aging, researchers report.

The study, in Neurology, included 3,287 men and women, ages 23 to 35, whose income was tracked from 1990 to 2010. At the end of the study, the participants took tests of mental ability and underwent M.R.I. examinations.

About a third of the group had one drop of 25 percent or more from their average income, and 399 had two or more. The more income declines a person had, the worse his or her performance on tests of processing speed, planning and organization.

After adjusting for sex, race, body mass index, blood pressure, smoking and other health and behavioral characteristics, they found that compared with no income drops, having two or more was associated with smaller total brain volume and lower white matter volume.