New research delivers fresh hope for everyone who struggles with a fading memory: Neurons continue to form well into old age, even in people with mental impairments or Alzheimer's disease.

"We found that there was active neurogenesis [new neurons forming] in the hippocampus of older adults well into their 90s," said study author Orly Lazarov, a professor of anatomy and cell biology at the University of Illinois at Chicago.

"The interesting thing is that we also saw some new neurons in the brains of people with Alzheimer's disease and cognitive [thinking] impairment," she added in a university news release.

The findings could lead to new treatments for mental decline in older adults, the researchers said.

In the study, Lazarov and her colleagues examined hippocampus tissue from the brains of 18 people, average age 90.6 years, after they died.

The hippocampus is involved in the formation of memories and in learning.

On average, there were about 2,000 neural stem cells and 150,000 developing neurons in each brain.

While people with mental impairments and Alzheimer's disease did have new neurons, their levels were significantly lower than in people with normal brain function, the researchers noted.

This is the first evidence of significant numbers of neural stem cells and newly developing neurons in the hippocampus of elderly adults, even in those with disorders that affect that part of the brain.

The researchers also found that people who scored better on tests of mental skills had more newly developing neurons in the hippocampus than those who scored lower on the tests, regardless of the level of disease in the brain.

"The mix of the effects of pathology and neurogenesis is complex and we don't understand exactly how the two interconnect, but there is clearly a lot of variation from individual to individual," Lazarov said.

"The fact that we found that neural stem cells and new neurons are present in the hippocampus of older adults means that if we can find a way to enhance neurogenesis, through a small molecule, for example, we may be able to slow or prevent cognitive decline in older adults, especially when it starts, which is when interventions can be most effective," she said.

The findings were published May 23 in the journal Cell Stem Cell.