They believe their results are down to the rich antioxidant levels in concentrated apple juice.
While studies in humans are needed to confirm the benefit to ageing people, the new research adds to previous evidence that fruit and vegetable intake might be good for an ageing brain.
"This new study suggests that eating and drinking apples and apple juice, in conjunction with a balanced diet, can protect the brain from the effects of oxidative stress - and that we should eat such antioxidant-rich foods," said lead researcher Dr Thomas Shea.
The team from the University of Massachusetts Lowell previously showed the benefits of feeding apple juice in mice bred to be prone to Alzheimer's disease.
But the new tests were carried out on mice designed to represent the normal ageing process.
The study, funded by the apple industry in the US, initially measured the different reactions by normal adult mice and ageing mice to a deficient diet.
Mice aged 9-12 months old were unaffected by the diet, which was lacking in folate and vitamin E and had iron to act as a pro-oxidant.
However the older mice, aged 2-2.5 years old, demonstrated statistically-increased oxidative damage and poorer performance in a Y maze test. This is consistent with normal ageing due to oxidative neurodegeneration, according to the researchers.
But when the elderly mice were fed apple juice concentrate, the human equivalent of two to three cups of apple juice per day, they performed significantly better on the maze tests and all had less oxidative brain damage than those on a standard diet, report the authors in the December 2005 issue of the Journal of Alzheimer's Disease (vol 8, no 3, pp283-287).
Supplementation by apple juice also protected the aged mice from the oxidative stress caused by the nutrient-deficient diet.
"We believe that this effect is due to the apple's naturally high level of antioxidants," said Shea.
Earlier investigations had determined that it is not the sugar and energy content of the apple juice, but the antioxidant attributes of apple juice that are responsible for the positive effects.
A number of epidemiological trials have found that people with a higher intake of fruits and vegetables are less prone to age-related cognitive decline, including conditions like Alzheimer's.
However there is little evidence to date that supplements containing purified antioxidants like the vitamins E and C can offer the same benefit. Some researchers believe that fruits and vegetables may contain specific compounds that act synergistically to fight oxidative damage.