Paris - Lab tests in which elderly mice were injected with a protein found in human umbilical cord blood have thrown up an intriguing target for keeping the brain healthy into older age, scientists said on Wednesday.The protein of interest, TIMP2, has previously been found to play a role in developing the hippocampus - the part of the brain that enables spatial navigation and processes memories.TIMP2 is plentiful in the plasma of umbilical cords, but levels of it decline with age.A team led by Tony Wyss-Coray at Stanford University in California injected ageing mice with TIMP2.The injections boosted activity in the rodents' hippocampus, and their learning, memory and ability to adapt to new information all improved, notably in their ability to extract themselves from a lab maze.TIMP2 - or the brain cells that the protein acts upon - could be useful targets for drugs to fight cognitive decline among the elderly, according to the study, published in the journal Nature.Outside commentators said the findings were exciting, but a hefty dose of caution was needed."The study shows that a human protein can reverse cognitive ageing in mice," said Jennifer Wild, a researcher in clinical psychology at Britain's Oxford University."This does not mean that the protein can cure dementia or cognitive ageing in humans," she told the London-based Science Media Centre (SMC).Alzheimer's experts said that the success with the lab mice touched on cognitive decline that comes naturally in ageing. "Although the treatments tested here boosted some aspects of learning and memory in mice, we don't know how relevant the findings might be to people," said David Reynolds, chief scientific officer at Alzheimer's Research UK."This research, while interesting, only looked at memory and thinking changes caused by ageing, and not those involved in dementia."Alzheimer's disease is the most common form of dementia, affecting about 47 million people worldwide, and has no cure and no effective treatments.