This news comes from The Rotman Research Institute at Baycrest and the University of Toronto, where scientists compared brain function in young, middle-aged and older adults.
"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.
The study says these findings add to the growing belief by scientists that two regions in the brain's frontal lobes gradually shift into a "seesaw imbalance," which causes older adults to become less efficient at blocking distracting information than young people are.
Concentration Ability Declines with Age
The study found significant differences between concentration abilities in old and young people.
- 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. (See the illustrated brain.)
- Dr. Grady's team reported that starting in middle age (40-60 years), 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.
- This imbalance becomes more pronounced in older adults (age 65+), which could explain their reduced ability to ignore distracting or irrelevant information.
"Our fMRI scanning reveals that middle age represents the transition between the patterns observed in youth to that found in old age," says Dr. Grady. "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."p]
How the Concentration Study was Conducted
While previous studies 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 used fMRI on normal, healthy middle-aged adults, as well as young and old adults, to understand how brains change in middle age.
- Twelve young adults (20-30 years), 12 middle-aged adults (40-60 years) and 16 older adults (65-87 years) participated in a series of memory tasks. The groups all had an average of post-secondary education.
- The first set of memory exercises involved looking at common nouns and pictures of objects of different sizes. By pushing one of two buttons, participants could decide whether words were printed in capital letters or lower case, whether pictures presented were large or small, and whether the pictures or words corresponded to living or nonliving entities. This tested participants semantic and perceptual judgment.
- Participants were then administered scanned recognition tests made up of words written in lowercase letters, including words to describe the pictures they had seen. This assessed semantic and perceptual recall.
- During all the memory tasks, their brains were scanned using fMRI which constructs computerized images of brain structures and pinpoints the areas being activated during a memory task.
Want a suggestion from Dr. Grady about how older adults can protect themselves? See page 2.
