Whether slapped on a car bumper or scrawled in a high school yearbook, the pledge to “never forget” may be true metaphorically, but it’s a lie.

Images and details of significant or traumatic events a graduation, a parent’s death, a president’s assassination, the Sept. 11 terrorist attacks will stay with people for many years, memory researchers say.

Yet specific recollections of what we were doing, who we were with and what we talked about and felt will fade and become distorted by time.

“We are constantly rewriting and redrawing our memories,” says Henry Roediger III, chairman of the psychology department at the Washington University in St. Louis. “It is not like calling up fixed events. It is more like an artist painting on a canvas taking some liberties, embellishing things here, leaving things out there.”

Most people think of memory as something that helps us recall that Columbus set sail in 1492, but scientists say this form of memory is just one of many types, orchestrated through neural networks that operate in different areas of the brain.

In many cases, Roediger says, we are not conscious of the mechanisms at work, any more than we are aware that the three-dimensional image we get from our vision is actually the merger of separate two-dimensional images for our eyes.

Harvard memory researcher and author Daniel Schacter notes that psychologist Ulric Neisser once said we reconstruct memories the way a paleontologist re-creates the images of a dinosaur from a few shards of bone.

Blank spots in a memory’s skeleton are filled in with educated guesses and assumptions, sometimes based on experiences that may have occurred after the event being remembered, Schacter says.

And sometimes the brain gets it wrong.

Roediger helped devise a simple test to illustrate just how easy it is to create false memories. He asked subjects to carefully memorize a long list of words, such as awake, nap, rest, slumber, dream, bed.

When questioned later, the majority of people swore, incorrectly, that “sleep” was among the words on the list.

“Human beings are built to make inferences, and we are great at it,” Roediger says.

Yet the memories of both young and older people are easily corrupted by suggestion.

As Roediger puts it in an article he wrote about his work, “The idea that our memories hold a literal record of our past, like a video recorder, is wrong.

“Remembering is a constructive process,” he adds, “and illusions of memory are the result of our struggle to weave the remembered pieces of our past into a coherent narrative story.”