The finding will enable the researchers to explore strategies for enhancing brain function in the healthy aging population, through mental training exercises and pharmaceutical treatments.
Conducted by University of California, San Francisco and University of California, Berkeley scientists, the research is based on the team's seminal 2005 discovery that the brain's capacity to ignore irrelevant information diminishes with age.
The capacity to ignore irrelevant information -- such as most of the faces in a crowded room when one is looking for a long-lost friend - and to enhance pertinent information -- such as the face of a new acquaintance met during the search for the old friend - is key to memory formation. This process is known as top-down modulation.
In this study, the team used electroencephalography (EEG), which measures the speed of neural processing, to examine the relationship between this inhibitory deficit hypothesis of normal aging and another leading hypothesis - that the brain's ability to process information quickly, diminishes.
The theory states that if information is not moving quickly onto the brain's conveyor belt, of sorts, there will be a backup of data, and this, in turn, will delay later information processing that will disrupt memory formation.
The new study revealed that both brain processes - the capacity to ignore irrelevant information and the ability to process information quickly -- diminished with age and, in fact, worked in tandem.
"The study showed that the brains of older adults have a deficit in suppressing irrelevant information during visual working memory encoding, but only in the first tenth to two tenths of a second of visual processing," said the lead author of the study, Adam Gazzaley, MD, PhD, assistant professor of neurology.
Also, despite the aging brain's ability to suppress extraneous information in the ensuing milliseconds, the memory deficit persists.
This means that interference by irrelevant information apparently overwhelms a limited working memory capacity, which is the ability to hold information in mind for brief periods of time to guide your actions.
However, what causes the break down in inhibition and processing speed, is something scientists are unaware of. But they know that in the course of aging, there are changes in the structure of neurons, the density of neural tissue and the actions of neurochemicals acting on the cells.
They also know that there are changes in the neural connections between neurons in far flung parts of the brain.
In the healthy aging brain, these changes are subtle. In the brains of those with mild cognitive impairment and the more severe form of impairment, such as Alzheimer's disease, they are substantial.
The team is now trying to relate how these changes might affect changes in inhibition and processing speed.
The study is reported in the current online early edition of Proceedings of the National Academy of Sciences.