"This could have exciting implications for the rehabilitation of memory," said one of the researchers, Dr Randy McIntosh at the University of Toronto's Department of Psychology.

"The older brain is more resilient than we think," he added.

"Thinking tasks"

The study compared which areas of the brain were used to perform the same "thinking task" by 10 young adults (aged 20 to 30) and nine older adults (aged 60 to 79).

It was carried out by Rotman Research Institute, Toronto, the University of Toronto and Brandeis University, Massachusetts, US, and is published in the journal "Current Biology".

The participants were shown two grid patterns and a few seconds afterwards were asked which had been the more dense. Whilst they did this, their brain activity was measured using positron emission tomography.

This measures the blood flow in the brain and marks out the brain areas which are "lighting up" during the memory task.

Equal results

The older participants did just as well as the younger ones in the tests. However the neural systems underpinning their performance were quite different.

There was some overlap in the brain regions used - the occipital, temporal and inferior prefrontal cortices - but the neural communication among these common regions was much weaker in the older individuals.

The older people compensated for this weakness by using other areas of the brain, including the hippocampus and dorsal prefrontal cortices.

Scientists are particularly fascinated by the older brain's activation of the hippocampus because this area is generally used for much more complicated memory tasks, such as learning lines from a Shakespeare play.