WASHINGTON — Memory and thinking skills naturally slow with age, but now scientists are peeking inside living brains to tell if depression might worsen that decline – and finding some worrisome clues.

Depression has long been linked to certain cognitive problems, and depression late in life may even be a risk factor for the development of Alzheimer’s. Yet how depression might harm cognition isn’t clear.

One possibility: Brain cells communicate by firing messages across connections called synapses. Generally, good cognition is linked to more and stronger synapses. With cognitive impairment, those junctions gradually shrink and die off.

But until recently, scientists could count synapses only in brain tissue collected after death.

Yale University scientists used a new technique to scan the brains of living people – and discovered that patients with depression had a lower density of synapses than healthy people the same age.

The lower the density, the more severe the depression symptoms, particularly problems with attention and loss of interest in previously pleasurable activities, Yale neuroscientist Irina Esterlis said Thursday at a meeting of the American Association for the Advancement of Science.

Esterlis wasn’t studying just seniors but a range of ages, including people too young for any cognitive changes to be obvious outside of a brain scan – on the theory that early damage can build up.

“We think depression might be accelerating the normal aging,” she said.