The link between surgery and cognitive decline in older patients may not be as strong as originally thought, new research suggests.

Researchers examined 575 patients who volunteered for the Washington University Alzheimer’s Disease Research Center, which collects cognitive data annually from adults aged 50 and older. Using the patients as their own control group, researchers analyzed how each person functioned for years both before and after a surgery. In comparing the groups of seniors to each other and to themselves, researchers “did not detect any evidence of a long-term cognitive decline” in older surgical patients, report authors say.

Previous studies of the link between surgery and cognitive decline typically test patients just before surgery, and then again months later. Under that approach, if a patient is beginning to develop dementia before the surgery, the follow-up exam could potentially attribute the decline to the surgery itself, not the existing dementia, researchers suggest. The study appears in the November edition of the journal Anesthesiology.