A study looking at brain function in young, middle-aged and older adults has identified changes in brain activity that begin gradually in middle age - and which may explain why older adults find it difficult to concentrate in busy environments and filter out irrelevant information.
The findings, by scientists at The Rotman Research Institute at Baycrest and the University of Toronto, are reported in the February 2006 issue of the Journal of Cognitive Neuroscience (Vol. 18, No. 2).
"It's known that older adults are more easily distracted. We think we've found a mechanism in the brain to explain this and generated new insight into when in the lifespan these brain changes begin to occur," says senior Rotman scientist and lead author Dr. Cheryl Grady.
While previous studies have used functional magnetic resonance imaging (fMRI) to look at how brains function differently in young and old adults, and patients with Alzheimer's Disease, this is the first time investigators have used fMRI on normal, healthy middle-aged adults, as well as young and old adults, to understand how brains are changing in the in-between years. Investigators administered a series of memory tasks to the three age groups to assess if age-related changes in brain function are task-specific, or generalized across a number of regions during memory tasks.
The findings add to the growing body of science that implicates two regions in the frontal lobes that gradually shift into a seesaw imbalance - causing older adults to become less efficient in inhibiting distracting information. In younger adults, activity in the dorsolateral prefrontal cortex (associated with tasks that require concentration, such as reading) normally increases during the task, while activity in the medial frontal and parietal regions (associated with non-task related activity in a resting state, such as thinking about yourself, what you did last night, monitoring what's going on around you) normally decreases.
However, starting in middle age (40-60 years), Dr. Grady's team noted that this seesaw pattern begins to break down during performance of memory tasks. Activity in the medial frontal and parietal regions stays turned on while activity in the dorsolateral prefrontal cortex decreases. The imbalance becomes more pronounced in older adults (65+), which could explain their reduced ability to ignore distracting or irrelevant information, she says.
"Our fMRI scanning reveals that middle age represents the transition between the patterns observed in youth to that found in old age. The seesaw imbalance in the two frontal lobe areas is not as significant as in older adults, but the functional changes are detectable by middle age."