Age, emotion, attention factor into memory
(CNN) -- The capitals of all 50 states. The name of your second-grade teacher. The location of your keys.
Know them all? Thank -- or blame, as the case may be -- your memory.
Details, impressions and opinions constantly bombard our brains, a torrent of information and stimulation that gives people fodder for memories that help define them and help them define the world. (For more, watch CNN at 10 p.m. ET Sunday for "Memory," a Dr. Sanjay Gupta primetime special)
"Everything that we do as human beings is based on our memories -- our experiences, our ability to communicate, ... our aspirations," said James McGaugh, a neurobiologist at the University of California, Irvine. "Memories are essential to life ... They are who each of us happens to be."
But even as scientists make strides in understanding the complex process, Americans' struggles with memory loss may be getting worse, particularly as life expectancies rise.
Some 4.5 million have dementia tied to Alzheimer's disease, a figure that could surge to between 11.3 and 16 million by 2050, according to the Alzheimer's Association. Millions more have mild cognitive impairment, increased memory loss that is often a precursor to Alzheimer's. (Health Library: Alzheimer's)
Memory loss fears -- and a desire to get ahead by being able to recall more information, more quickly -- have spawned scores of products and services. Mental exercises (as detailed in books and other media) purport to help, as do certain foods. Experts say that "memory-boosting" drugs could soon flood the market.
"This is a source of great worry for some people," said Harvard psychology professor Daniel Schacter. "Without memory, we wouldn't be able to perform basic skills. We wouldn't have a sense of self. We wouldn't be able to remember our personal experiences."
A complex process
Films such as "Eternal Sunshine of the Spotless Mind," "50 First Dates" and "The Bourne Identity" speak to how memory loss can capture the public's imagination.
For some, however, the problem is all too real.
Chuck Ozug lives entirely in the moment. Since a cardiac arrest damaged his brain, the 53-year-old has been unable to form memories -- the date, the news, even the start of a phone conversation.
With support from his wife, Marianne, the former high school English teacher fills the void by doing puzzles, reading the Boston Globe and writing poetry.
"My memory like snowflakes. Soft, faint snowflakes. Soothing only for a while," he writes.
One of the most famous characters in the study of memory is known in scientific circles as "H.M." In 1953, the then-27-year-old Connecticut native (who is still alive) had part of his brain removed to control seizures -- and lost his ability to form long-term memories.
Such cases and other research shed light on the roles played by specific brain structures and connections (electric impulses that pass along information between brain cells). (Interactive: How memory works)
Final recollection might incorporate sights, sounds, smells, emotions and other views from that specific moment, as well as afterward. Memories become strengthened (or weakened) over time, a process during which they can be distorted, forgotten or falsely reinforced.
"Memory is not a simple replay," Schacter said. "The bits of information that we recover from the past are often influenced by our knowledge, beliefs and feelings."
Strong emotions, strong memories
Ozug, who has lost his ability to create long-term memories, does puzzles to sharpen his mind.
National Guard Spc. Esteban Lora spent much of 2003 in Iraq's Sunni Triangle, battling insurgents and seeing friends wounded in attacks.
Now, back home and attending college in Miami, Florida, he is fighting his memories.
"I was angry. I was very emotional," Lora said of his feelings after returning stateside.
A study released in July in the New England Journal of Medicine, suggests Lora is not alone: 20 percent of U.S. combat troops in Iraq have post-traumatic stress disorder (PTSD), anxiety or depression. With PTSD, small stimuli can unleash a flood of painful memories -- which, with nightmares, can lead to jumpiness, anger, depression and intense stress.
"In combat situations, it's appropriate to have an increased fear response," said Emory University professor J. Douglas Bremmer. "PTSD is a failure to learn how to turn that off."
This disorder speaks to the major role emotion and stress play in reinforcing memories as they are repeatedly recalled -- and, sometimes, reinvented.
A study tracking tough mock interrogations at Fort Bragg, North Carolina, home to the U.S. military's elite survival school, found less than half of trainees correctly identified their interrogators after the fact. This analysis, led by Yale psychiatrist Andy Morgan, suggests that stress often diverted people's focus -- thus, their ability to comprehensively remember details.
As PTSD research suggests, psychological issues arise not only from recalling details, but also emotions that (unlike other aspects of memories) do not fade. That would also mean people will often have better recollections of positive emotional experiences, like a wedding.
A study said 20 percent of U.S. combat troops in Iraq have anxiety, depression or PTSD, like Lora.
"If something's highly significant to you personally, you are going to be emotionally excited about it," McGaugh said. "This is not making perfect memories, this is making stronger and longer-lasting memories."
Selective and effective
Forgetting is an important -- some experts say, essential -- part of memory, and not just to avoid being haunted by negative past experiences.
"We don't want a memory that is going to store every bit of every experience," Schacter said. "We would be overwhelmed with clutter of useless trivia ... We're probably better off having ... a more selective coding of info."
Human memory may not store every fact, but it does well to give people a general sense of their experience, adds Schacter.
To do this, memory pulls from past incidents -- consciously and subconsciously -- to tell you, for example, that a given situation feels dangerous or a certain food might make you sick.
That said, many work hard -- spending time and money -- to memorize as much as possible, employing techniques such as visualization and intense memory "drills."
Take 6-year-old Abby Julo, for example. With her father's coaching, the kindergartener knows the names of world leaders, the U.S. Cabinet, all U.S. presidents and first ladies, constitutional amendments and Martin Luther King's "I have a dream" speech.
Abby Julo, 6, knows the names of all U.S. presidents, first ladies and more -- evidence of memory's potential.
"You first learn, and then remember, and then get it forever," Abby said.
Dr. Gary Small has made a career "boosting" memories, with his books and 14-day "boot camps for the brain" (run by the Memory Fitness Institute) in Fountain Valley, California.
"If you reduce stress, eat a healthier brain diet [singling out foods like spinach, blueberries and salmon], get aerobic activity each day, that is going to protect your brain and possibly lower your risk for Alzheimer's disease or at least delay the outset," Small said.
Although a few studies suggest such approaches bolster long-term memory, skeptics abound.
"Those are helpful things, but whether it would give you complete protection is unlikely," said Dr. Eric Kandel, who won a Nobel Prize for his research on memory.
For all that we still forget, experts said, the brain's ability to encode and rehash experiences, lessons and details not only sets humans apart from other creatures, but also from one another.
"It's extraordinary," Kandel said. "It's the glue that ties the fabric of life together. I can sit here and do mental time travel ... move back and forth in my mind, between different events that have occurred because of the powers of memory."