When US scientists introduced stem cells to the damaged brains of live mice, they were surprised by the results: the treated mice scored significantly better on learning and memory tests than their untreated peers.
The study is among a few that offer some hope of methods to heal brain impairment and prevent memory degradation.
The mice experiment, conducted at the University of Wisconsin-Madison and published in this month's issue of Nature Biotechnology, is the first to show that human stem cells can successfully heal "neurological deficits", according to the lead author, Professor Zhang Su-chun.
The researchers from the university's Stem Cell and Regenerative Medicine Centre damaged a part of the mice brains involved in learning and memory. Then they transplanted lab-cultured human embryonic cells ("mother cells" that have the potential to become any type of cell in the body) in the brain, where the stem cells formed two vital types of brain cells.
"These two neuron types are involved in many kinds of human behaviour: emotions, learning, memory, addiction and other psychiatric issues," says Zhang, a pioneer in this field.
Though stem-cell therapy is unlikely to completely repair the brain, it does hold promise for disorders such as Alzheimer's disease, Down's syndrome, schizophrenia, epilepsy, depression and addiction.
For people who don't suffer from these conditions, there's the tantalising chance of retaining sharper memory into old age.
In another study published recently in The Journal of Neuroscience, scientists at the University of Texas Health Science Centre at Houston reversed memory loss in sea snails' brain cells.
This was done by determining when the cells were prime for learning, then retraining the cells through an optimised schedule.
"This method may apply to humans if we can identify the same biochemical processes," says the study's senior author, John Byrne.
"Mathematical models might help design therapies that optimise the combination of training protocols with drug treatments," he says.
The gradual decline of memory is part of the ageing process - it tends to peak in one's 20s, then levels off, declining steeply in one's 80s.
Some types of memory, however, such as semantic memory (the ability to recall concepts and facts) or procedural memory (how to do tasks), stay constant or may even improve in old age, according to the American Psychological Association.
Episodic (which captures the what, where and when of our daily lives) and longer-term memory decline with age.
The ability to process information, learn something new or multitask also typically slows down as we grow older.
These memory skills are found in different parts of the brain. The hippocampus is particularly important for remembering events, the basal ganglia for skills and the amygdala for emotional memory. This is why different types of brain injuries can result in different kinds of memory problems, according to Jordan Poppenk, a post-doctoral research fellow at the Princeton Neuroscience Institute.
For example, excessive drinking, road accidents and carbon monoxide poisoning can cause trauma to the hippocampus.
These lesions to the hippocampus "can result in the loss of ability to remember new things", says Eric Chen, a clinical professor from the department of psychiatry at Hong Kong University. "Recent memories that have not been well-consolidated may be lost, too. However, distance memory usually remains intact."
Poppenk says the best way to measure your memory ability is to "take a standard neuropsychological test, which allows you to compare your memory against that of other healthy people your age".
But he says the tests are "blunt instruments" as they measure only one type of memory and the person's results will be affected by "whether you woke up on the wrong side of the bed, missed your morning coffee, the time of day and many other factors".
People who experience serious memory problems should consult a neurologist.
Another question scientists are probing is why some people have better memory than others. It could be for many reasons, Poppenk says, from having a larger posterior hippocampus to simply having more knowledge about the issue or task at hand.