As the brain begins to shrink with age, it increases communication between the two brain hemispheres to help older people compensate for the negative aspects of ageing, new research has found.

"This study provides an explicit test of some controversial ideas about how the brain reorganises as we age," said lead author Simon Davis, assistant professor at Duke University, Durham, North Carolina."These results suggest that the ageing brain maintains healthy cognitive function by increasing bilateral communication," Davis added. For the study published in the journal Human Brain Mapping, the researchers used a brain stimulation technique known as transcranial magnetic stimulation (TMS) to modulate brain activity of healthy older adults while they performed a memory task. When researchers applied TMS at a frequency that depressed activity in one memory region in the left hemisphere, communication increased with the same region in the right hemisphere, suggesting the right hemisphere was compensating to help with the task.

In contrast, when the same prefrontal site was excited, communication was increased only in the local network of regions in the left hemisphere. This suggested that communication between the hemispheres is a deliberate process that occurs on an "as needed" basis.Furthermore, when the authors examined the white matter pathways between these bilateral regions, participants with stronger white matter fibres connecting left and right hemispheres demonstrated greater bilateral communication, strong evidence that structural neuroplasticity keeps the brain working efficiently in later life.

"Good roads make for efficient travel, and the brain is no different. By taking advantage of available pathways, ageing brains may find an alternate route to complete the neural computations necessary for functioning," Davis said.These results suggest that greater bilaterality in the prefrontal cortex might be the result of the ageing brain adapting to the damage endured over the lifespan, in an effort to maintain normal function.