In his old age, American humorist Mark Twain once mused that his mental faculties had decayed such that he could remember only things that never happened.
“When I was younger, I could remember anything, whether it happened or not,” Twain wrote. “But my faculties are decaying now and soon I shall be so I cannot remember any but the things that never happened. It is sad to go to pieces like this, but we all have to do it.”
The human brain
Modern science has confirmed Twain’s conjecture — research shows that memory skills tend to decline dramatically in old age, with decreasing levels of accuracy and increasing errors. However, new research from Washington University in St. Louis suggests age-related cognitive decay may not be as inevitable as Twain contended.
“Our study suggests that the failing memories of older adults, including their tendency to remember things that never happened, are not an inevitable consequence of aging,” said Henry L. “Roddy” Roediger III, study co-author and the James S. McDonnell Distinguished University Professor at Washington University.
In research presented Aug. 8 at the American Psychological Association meeting in Toronto, Roediger provides evidence that false memories and other cognitive declines often associated with normal aging can be more directly linked to measurable declines in executive control functions in the frontal lobes of the brain.
“We tested a group of adults with an average age of 75 years and found that about one out of four had managed to avoid the memory declines so common in older adults,” said Roediger. “Older adults who maintain high frontal lobe function were shown to have memory skills every bit as sharp as a group of college students in their early 20s.”
Roediger, a leading expert on human memory, has focused recent research on understanding cognitive processes behind the creation of false memories, also known as memory illusions. Human memory, he explains, is not a storehouse of crystal clear, video images available for immediate and 100 percent accurate recall. Instead, memories are recalled through a constructive process that retrieves sights, sounds, words and other seemingly pertinent information, weighs their relevance to the memory task at hand, and then weaves them into a “best available” representation of a past experience.
Veridical memories are those that generally conform to reality — memories that provide a relatively true and accurate representation of a past experience. False memories occur when we remember events differently from the way they occurred, or in the most dramatic cases, when we remember events that never happened. False memories often result when we mistakenly merge elements of various past experiences or when imagination is used to fill holes in a sketchy recollection.
“There has been a lot of research in recent years that suggests deterioration in the prefrontal cortex is linked to age-related declines in veridical memory, but this is the first study to firmly establish a similar link to increases in false memories,” Roediger said. “The idea that frontal lobe decline is associated with susceptibility to false memories is relatively new.”
Although we’re all susceptible to false memories, the increased vulnerability associated with aging has serious implications for day-to-day challenges faced by older adults. Those on daily medications often admit difficulty recalling whether or not they took a scheduled dose. Telemarketing scams aimed at the elderly often are fashioned to take advantage of failing memory skills. And, while the elderly are more likely to be targets of crime, their susceptibility to false memories might raise doubts about their ability to provide eyewitness testimony in court cases.
When it comes to memory, it’s clear that all people are not created equal. Test the memory skills of a random sampling of young healthy adults and you’ll find wide individual differences in memory abilities. Test older adults and you’ll find that this variance in individual skills levels has grown much greater. Interestingly, while some older adults hold onto their memories, exhibiting skills on a par with the average young adult, other older adults show dramatic declines.
Several theories exist for why false memories increase with age. One suggests that older adults fail to properly encode information as an event is experienced or have problems retrieving and sorting through such details during recall – a problem known as source monitoring.
A related theory suggest frontal lobe problems make it difficult for older adults to focus attention on the memory task at hand and to effectively place retrieved information in the proper context. That is, frontal lobe functioning underlies the ability to monitor accurately the source of information, and when frontal lobe functioning declines, so does memory for the source of the events.
“If the frontal lobes are responsible for controlling attention or source monitoring, such that false memories can be distinguished from true memories, then we thought it possible that older adults with high frontal lobe function scores would not show greater false recall,” Roediger said. “The idea here is that the increased susceptibility for memory illusions with older adults is carried by older adults with relatively low frontal lobe function. Our findings support this theory.”
Previous research has attempted to establish a clear link between diminished frontal lobe function and increased false memories, but these experiments may have failed, suggests Roediger, because methods used did not effectively assess whether an older adult had relatively high or low frontal lobe function.
Roediger’s team addressed this issue by assessing each participant using a composite score from performance on a battery of five neuropsychological tests, each previously shown to measure some facet of frontal lobe function. Once categorized as high- or low-function, older adults in the study were tested again to see how each fared in experiments designed to lure them into the creation of false memories.
In one test, researchers used a standard list of 22 bird names that people mention most often when asked to list as many types of birds as they can recall. Researchers provided subjects with the names of 17 birds drawn from the norm, but left out the five most-often mentioned bird names. Later, when asked if the name of a particular bird had been presented, some participants developed a false memory –recalling one or more of the top five bird names as included in the original list.
In another experiment, researchers created an eyewitness scenario by showing a video of a workman stealing a wallet from an office desk. Researchers then interviewed subjects and casually introduced some misinformation about what was seen on the video. Some subjects took the lure and included the misinformation in their “eyewitness” accounts of how the robbery took place.
As a benchmark, researchers conducted the same tests on a group of college students in their early 20s. Surprisingly, older adults with high frontal lobe function performed virtually as well as their young counterparts, both in terms of recalling real events and in avoiding traps designed to induce false memories.
Although the study identified significant differences in memory performance among older adults with relatively high or low frontal lobe function, it’s important to note that each of the 36 older adults in this study might be considered as high functioning when compared to the general population of older adults, Roediger said.
“Our older adult study group includes many retired academics and most have high levels of education. All of them drove themselves to the experiments and were excited to be taking part,” Roediger said. “On measures of knowledge, such as vocabulary, many of the older adults in our study outscored the college students. ”
Thus, while this study found that one-in-four adults had memory skills as sharp as college students, that ratio most likely would not hold true in the general population. Skill levels are likely to be much different in a sample of older adults at the local nursing home.
“In terms of appearance, conversation skills and other surface measures, it’s very difficult on first impression to tell which of the older adults in this study have high frontal lobe function and which have relatively lower function,” Roediger said.
“Although the differences are subtle, it is interesting to speculate as to why some of these older adults have been able to retain their executive processing skills. It’s possible that those with diminished cognitive functioning are on their way to developing Alzheimer’s, but it’s impossible to say based on this experiment.”
In future research, Roediger and colleagues will be looking for clues about what is causing age-related declines in frontal lobe function. They also hope to identify and test techniques that could help older adults compensate for age-related exaggerations in memory illusions.