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By all accounts, my grandfather Nathan had the comic ambitions of a Jack Benny but the comic gifts of a John Kerry. Undeterred, he always kept a few blank index cards in his pocket, so that if he happened to hear a good joke, he'd have someplace to write it down.

How I wish I knew where Nathan stashed that deck.

Like many people, I can never remember a joke. I hear or read something hilarious, I laugh loudly enough to embarrass everybody else in the library, and then I instantly forget everything about it — everything except the fact, always popular around the dinner table, that "I heard a great joke today, but now I can't remember what it was."

For researchers who study memory, the ease with which people forget jokes is one of those quirks, those little skids on the neuronal banana peel, that end up revealing a surprising amount about the underlying architecture of memory.

And there are plenty of other similarly illuminating examples of memory's whimsy and bad taste — like why you may forget your spouse's birthday but will go to your deathbed remembering every word of the "Gilligan's Island" theme song. And why you must chop a string of data like a phone number into manageable and predictable chunks to remember it and will fall to pieces if you are in Britain and hear a number read out as "double-four, double-three." And why your efforts to fill in a sudden memory lapse by asking your companions, "Hey, what was the name of that actor who starred in the movie we saw on Friday?" may well fail, because (what useless friends!) now they've all forgotten, too.

Welcome to the human brain, your three-pound throne of wisdom with the whoopee cushion on the seat.

In understanding human memory and its tics, Scott Small, a neurologist and memory researcher at Columbia, suggests the familiar analogy with computer memory.

We have our version of a buffer, he said, a short-term working memory of limited scope and fast turnover rate. We have our equivalent of a save button: the hippocampus, deep in the forebrain is essential for translating short-term memories into a more permanent form.

Our frontal lobes perform the find function, retrieving saved files to embellish as needed. And though scientists used to believe that short- and long-term memories were stored in different parts of the brain, they have discovered that what really distinguishes the lasting from the transient is how strongly the memory is engraved in the brain, and the thickness and complexity of the connections linking large populations of brain cells. The deeper the memory, the more readily and robustly an ensemble of like-minded neurons will fire.

This process, of memory formation by neuronal entrainment, helps explain why some of life's offerings weasel in easily and then refuse to be spiked. Music, for example. "The brain has a strong propensity to organize information and perception in patterns, and music plays into that inclination," said Michael Thaut, a professor of music and neuroscience at Colorado State University. "From an acoustical perspective, music is an overstructured language, which the brain invented and which the brain loves to hear."

A simple melody with a simple rhythm and repetition can be a tremendous mnemonic device. "It would be a virtually impossible task for young children to memorize a sequence of 26 separate letters if you just gave it to them as a string of information," Thaut said. But when the alphabet is set to the tune of the ABC song with its four melodic phrases, preschoolers can learn it with ease.

And what are the most insidious jingles or sitcom themes but cunning variations on twinkle twinkle ABC?

Really great jokes, on the other hand, punch the lights out of do re mi. They work not by conforming to pattern recognition routines but by subverting them. "Jokes work because they deal with the unexpected, starting in one direction and then veering off into another," said Robert Provine, a professor of psychology at the University of Maryland, Baltimore County, and the author of "Laughter: A Scientific Investigation." "What makes a joke successful are the same properties that can make it difficult to remember."

This may also explain why the jokes we tend to remember are often the most cliched ones. A mother-in-law joke? Yes, I have the slot ready and labeled.

Memory researchers suggest additional reasons that great jokes may elude common capture. Daniel Schacter, a professor of psychology at Harvard and the author of "The Seven Sins of Memory," says there is a big difference between verbatim recall of all the details of an event and gist recall of its general meaning.