One of the surest ways to frustrate my mother was for her to accompany Grandma Ethel, then in her mid-90s, to her favorite delicatessen near the assisted-living facility she called home in Chicago. It had a menu as big as a billboard, and Ethel relished the chance to consider almost every dish before she settled on an old favorite, no matter how long the process took.

This familiar dynamic — an elderly parent who acts as though she has all the time in the world, and an adult caregiver with an eye on the clock — has a basis, as it turns out, in science. According to Gregory Samanez-Larkin, a postdoctoral fellow at Vanderbilt University and co-director of the Scientific Research Network on Decision Neuroscience and Aging, the way we make decisions changes on a fundamental, physiological level as we age. The brain begins to approach its tasks differently, and once we understand the changes, we can learn to work with them.

To research his doctoral dissertation at Stanford University, Dr. Samanez-Larkin focused on brain systems involved in computing value when making financial decisions. “These systems are at the core of making decisions,” he said. In one study, he studied brain activity among research subjects aged 20 to 85 as they considered a set of investment options.

In a second study, to be published this month, he looked at “decision aids” to determine what kind of information two groups — young people in their 20s and 30s, and people in their 60s and older — found to be most useful in making choices. The research subjects considered a set of risky or safe investment options as researchers measured their brain activity.

Compared with those of younger adults, the brains of older adults were more likely to deviate from standard decision-making patterns when confronted with difficult choices, Dr. Samanez-Larkin found. This may be a graphic representation of a phenomenon caregivers know too well, he said: an elderly person experiencing the act of decision-making as chaotic and overwhelming.

“This often leads to people opting out altogether, which can be extremely detrimental in a lot of cases,” he said. “There is some evidence that older adults are more likely to stick to defaults, or baselines, and this may be related to a desire to just avoid having to deal with the whole decision-making process.”

Processing information also gets more difficult for the elderly, said Dr. Samanez-Larkin. “We get more easily distracted and sometimes have a harder time ignoring irrelevant information. We have a harder time sourcing information — ‘Who was it that told me this was a good idea?’”

Older adults are also more focused on the present moment and maximizing well-being. That can make simply reading a menu a pleasurable experience, said Dr. Samanez-Larkin, but it may also lead a parent to resist change simply because it’s unfamiliar.

But the solution is not to tell a parent what she wants for lunch — or what she ought to do about anything else, for that matter. Dr. Samanez-Larkin advises caregivers to hew to a strategy that boils down to gentle nudging, an acknowledgment that people of any age usually prefer information to directives.

In the second study, Dr. Samanez-Larkin offered subjects two sets of information on which to base their financial decisions. The first was a set of graphical earnings thermometers that simply required the subject to pick the best win-to-loss ratio; the second was a line graph that revealed more information on earnings over time.

“They preferred the aid with more information,” he said. “It just felt better to them. They liked having helpful and relevant information.”

So: nudge gently, and do it with information, not directives. The one exception to this rule, importantly, occurs when a parent suddenly embraces a new or novel behavior that seems at odds with the rest of his or her personality. The outlier element, the surprising development, can be a sign of trouble and an indication that an adult child needs to get more actively involved, said Dr. Samanez-Larkin.

Every age brings its own peculiar shortcomings where finances are concerned, according to a study by a group of economists who looked at the financial errors people make — late credit card payments, for example — at different ages. Young people have loads of cognitive ability but little experience; elderly people have plenty of experience but diminished cognitive skills.

Middle age brings a valuable balance of ability and experience, researchers say. “Adult children are actually ideally suited to help an aging parent,” said Dr. Samanez-Larkin. We are, he said, at “a psychological prime, of sorts,” capable of being useful — so long as we remain supportive, and resist the urge to take over.

This post has been revised to reflect the following correction:

Correction: March 8, 2011