The MYSTERY of MEMORY : Why do we remember useless things forever while important ones vanish? New research offers some clues.

You can recall everything that happened during prom night, but you can’t remember where you left your keys last night.

You check your watch. Fifteen seconds later, you can’t remember the time.

The image of Grandma’s cute little white house is vivid in your memory--until you find a snapshot that shows it was yellow.

And just when you figure your memory is shot, you recall with ease where you put the lawn rake three years ago.

Human memory is a bewildering marvel, capable of miraculous feats and frustrating failures. But now, after what UC Irvine professor Gary Lynch calls “a bona fide scientific revolution over the last 10 years,” brain researchers are beginning to understand some of memory’s most basic workings.

Lynch, a psychobiologist at UCI’s Center for the Neurobiology of Learning and Memory, is among the world’s leading brain scientists. He and colleagues have discovered what they believe is the process by which memory is stored in the brain, and they have devised an experimental drug, Ampakine, which they say increases learning speed and retention in rats.

The university has licensed an Irvine pharmaceuticals firm to develop Ampakine as a possible prescription drug, hoping it will increase memory in mild cases of dementia, stroke and Alzheimer’s disease. So far, its effect in people is untested.

But this is only the latest development in brain research, Lynch says. A decade of discoveries now allows science to describe “with some degree of confidence things that would have sounded like science fiction 10 years ago. What we know now compared to just five years ago is incredible.”

Why is it you can remember the prom but not where you put your keys?

You are using two physically separate kinds of memory, Lynch says. The prom is engraved in your “episodic memory,” a very powerful system for preserving the rich details of events. The hormones released when you feel strong emotions intensifies these memories, and your hormones really pumped on prom night.

But the location of your keys was recorded in your “scratch-pad memory,” which is separate and notable for two qualities: You can’t store much information there, and the information evaporates quickly, usually within a few hours.

This also explains why you don’t remember the time only seconds after looking at your watch. As soon as the need for the information is gone, scratch-pad memory tosses it overboard.

But how could the memory of Grandma’s white house be so vivid yet so wrong?

Lynch says it is not known exactly how this happens. There is evidence that new memories can partially override old ones, so seeing a white house similar to Grandma’s yellow one might unconsciously tint the original memory.

It is also known that newly formed memories are, like unset concrete, vulnerable for a few hours. During that time, the brain can send a code that erases the new memory.

All this is more important than most people realize, Lynch says. Most people think of memory only as remembering to pick up milk on the way home. In reality, you use memory constantly.

You leave work and recognize your car among the hundreds in the parking lot. You remember how to open the door, how to start the engine, how to drive home. You hear a song on the radio and remember the emotions you felt when you first heard it. You see a red light and unconsciously remember that you’re supposed to stop.

“Memory is the device that organizes the world for you,” Lynch says. “Whatever you encounter, you will relate it to something in your experience--that is, to something you remember. You have to, because your brain’s just built that way.”

The brain is an unimaginable jumble of electrical circuits. Each of 10 billion brain cells connects with 50,000 others. One square millimeter of cortex, the crinkly surfaced dome of the brain, contains 80,000 brain cells, making the cortex the most complex electronic circuit board on Earth.

This means the brain’s memory storage capacity is effectively unlimited. You’d need many more than one lifetime to fill it up.

The brain can manage such an immense cargo of memories because it breaks the process into smaller jobs. What seems to you to be a single continuous action of remembering is actually many actions occurring in quick, seamless succession.

At the most basic level, the brain stores each memory in its own network of brain cells by changing how those cells behave. An electrical “learning code” is sent telling each cell to remember whatever immediately follows, such as the impulses from hearing a sound.

The cells record by turning themselves into more sensitive receivers. Now the cells have hair triggers, and when the brain goes looking for this memory, the network where it’s stored is much more likely to respond strongly.

The process is pure cause and effect--first comes the code, then the information to be remembered--and the process depends on a sense of time. Code pulses spaced too closely or too far apart will fail to turn on the memory apparatus.

Lynch suggests that this is the basic reason we have a sense of cause and effect, that we recognize (or imagine) that two things happening at different times can be related. “This is why when a door slams and the light goes out, you instantly assume the slam shut off the light. It’s inescapable, because it’s built right into our brain organization.”

Time has other effects on memory. Say ought , toe and mobile , and they’re recognized as three words. But the same sounds without pauses are recognized as one word.

Show your baby a teddy bear and he or she will remember the visual image. Say teddy at the same time and the word association is recorded as well. Then the sound teddy will summon up a visual memory of the teddy bear, a phenomenon Lynch believes is unique to human beings.

On the next level of memory, the brain is organizing memories according to physical similarities. Lynch says the design of brain circuits causes this to happen automatically, unconsciously and irresistibly. The process produces “phenomenally good categories,” much better than categories we could consciously devise, he says.

Until recently, brain scientists did not know this categorizing process was occurring, yet people use memory categories constantly, Lynch says.

Example: A friend asks, “What’s that on the limb?” You look, see an adolescent male English sparrow with a band around one leg and an insect in its beak, and you say, “It’s a bird.” Why are you withholding all that extra information?

Because at first glance, the brain goes only to the category it has made for such objects, Lynch says. The brain goes deeper for detail as a second step when detail is needed.

This makes more sense than you might think, Lynch says. “It’s an excellent survival technique. You walk out in the street and you see an object coming at you on four wheels with someone sitting in it. You’ve never seen this specific object before, but you instantly know it’s a car. You don’t stand there and say, ‘I believe that’s a ’37 Ford. Or perhaps a Chevy.’ You know it’s a car and you get out of the way.”

Yet consciously trying to define a car category, for example, is difficult, Lynch says. Try it, then see whether it would exclude a bus, a truck, a golf cart and a wheelchair. Yet such a sophisticated category was created in your brain, by your brain, without you realizing it.

Not only is the human brain capable of forming these categories, it cannot avoid doing so, Lynch says. Every encounter with something new requires the brain to fit it into an existing memory category.

You can experience this process any time you want. Stare at fleecy clouds or into a cottage-cheese ceiling, and soon your mind perceives images forming among the random patterns. Your brain is trying to organize the information from your eyes into something that will fit into one of your memory categories.

At the next higher level of memory, the cortex reaches outside itself to add emotional and muscular power to memory.

All parts of the cortex have electrical connections to other parts of the brain, but there are immense trunk lines running to specific regions.

One destination is the amygdala, which controls emotion. It doesn’t matter what you’re doing, smelling, seeing or thinking, if we stimulate one part of your amygdala, you’ll feel angry. Stimulate another and you’ll feel happy or sad or hungry or lustful.

The emotional effects of memory are stored here. Whenever you recognize or recall something, your cortex checks with the amygdala, which sets off whatever emotion has been earmarked for that memory or category, Lynch says. This is the reason string quartets might make you cry and movie theaters might make you hungry.

Other connections reach a region known as the striatum, where we organize our movements. Here recognition can bring fast action. When someone yells “Duck!” the striatum remembers what you’re supposed to do and it makes you duck before you can think.

So far, “We’re talking about circuitry that’s universal to mammals. It’s just as well developed in a rat’s brain as in yours,” Lynch says.

But a third region, the hippocampus, is much more developed in human beings.

“You don’t want to lose your hippocampus, and tragically enough, it’s probably the most vulnerable part of your brain,” Lynch says. “You have a heart attack, a stroke, and you can wipe it out. Then you can’t form any new memories--or very few.

“Actually, you could learn to ride a bicycle, but you’d never remember where you put it. We still don’t know why the hippocampus does that.”

But Lynch has published a hypothesis that the hippocampus adds additional kinds of memory seemingly needed to form ordinary memories in the cortex.

The first, which he calls “recency memory,” records the passage of time. “You run into someone, it’s Charlie, and you say, ‘Hey, Charlie, haven’t seen you in years.’ What happened was you recognized this person to be Charlie and then you checked the hippocampus to see how long it’s been since you saw him. That’s a powerful effect, and you know it immediately.”

The second powerful effect is knowledge of whether you’ve already been here and already done this. This is the scratch-pad memory at work, recording, for a short while only, routine matters that you’re not going to want to remember tomorrow: “Where did I park my car?” “Have I already checked the mail?” “What’s the phone number I just looked up?”

“This is a very imperfect device, and it may be because its memory is actually meant to be thrown away. The trick is to stay away from it when you need long-term memory,” Lynch says.

People who never forget where they put their keys are using tricks, consciously or unconsciously, such as always putting them in the same place, Lynch says. They depend on remembering a procedure, a ritual, which is a different, very stable form of memory outside the hippocampus.

The hippocampus’ third powerful effect is expectation or anticipation--memory of what the proper sequence of events should be. You meet Charlie and you say you haven’t seen him in years. If instead of returning your greeting Charlie starts tap-dancing and yodeling, you will immediately know something’s screwy.

“You instantly detect this prior to making any intellectual judgments or analysis,” Lynch says. “You instantly have a sense that something’s wrong, and it’s full stop, freeze, back up and what’s going on?”

The reaction is unavoidable, Lynch says. If you open your refrigerator and see piles of cash instead of food, your first reaction will be wariness, not joy.

“We are now going much deeper into the land of hypothesis,” Lynch says. “Now we’re into an area that is a little embarrassing for us brain scientists, because what I’m telling you is this: We don’t have much of an idea at all about what’s going on in 85% of your brain.”

The vast majority of the cells in the cortex do not connect to anything outside, Lynch says.

“This seems insane. Where’s all the real-world stuff--information from the eyes and the ears? That’s still going to small parts of the cortex, but the rest of the cortex is just hooked up to itself. It’s like a huge city where none of the streets leads to the outside.”

At the front of the cortex is an area involved in coordinating physical movement, from climbing a tree to speaking a language. This area must remember incredibly complicated instructions to accomplish these tasks.

At the back of the cortex are individual areas involved with vision, smell, sound and other perception.

Connections allow these two areas to talk to one another and to form associations. Consequently, hearing the word dog can summon up a mental picture of a dog, and you can scan it as you would a picture. These connections allowed Beethoven, even though he was deaf, to compose music by remembering the sounds of notes and instruments.

Lynch says no other mammal has anywhere near as many front-to-back connections. In a person, they are gathered in immense bundles, trunk lines “as big around as your finger,” Lynch says. He guesses that communication along these trunk lines was the ultimate evolution of the human brain.

Once this link existed, the complicated programs at the front that had been controlling movement could now communicate with the huge store of memories at the rear. The brain no longer needed the eyes to create vision. The memory of images could be coordinated in the same way. You could experience a walk to the store entirely within your imagination, arranging memories of what you saw, smelled, felt and heard on previous trips.

There could be language, because the memory of word sounds stored at the back could be arranged into phrases and sentences by programs at the front.

There could be foresight and planning, because remembered images, stored at the back, could be arranged into sequences, allowing the brain to preview actions. This is what high divers are doing when they seemingly go into a trance just before their dives. This is what novelists are doing as they devise a plot.

“I suspect it was the growth of this front-to-back thing that led to what we experience as thinking,” Lynch says. “You took those motor programs meant to help you climb trees, but you used it to organize the memory of climbing trees. You turned it inward. Of course, once this thing is clocking along, it never needs to do anything. It can go on forever.

“And here’s the irony to this argument. You tell me something, and I say to you, ‘What are the rules of grammar you just used? I mean, you just used them. You changed the pronunciation of this word because it followed that word, you had this sequence, you used this exception--what did you experience as you were doing it?’

“You’d have to sit down and think, but all you can do is analyze it. Because you didn’t actually experience anything. You just did it.

“So why are we so screwed up? Because in order to think, we run these programs, but our consciousness has no access to those programs. They’re organizing your memory and coordinating your thinking, but you have no conscious access to them.”

Memory at Its Most Basic Level

A. Eye: Sees object and sends electrical impulses to brain.

B. Visual cortex: On surface of the brain. Receives impulses, sends them to be recognized or recorded.

C. Neocortex: Surface of the brain. Stores most memories. At 10 billion brain cells, the capacity is so large you can’t fill it in a lifetime.

D. Amygdala: Inside the brain. Adds emotional meaning to memories, how you react to spiders or kittens.

E. Hippocampus: Inside the brain. Remembers time (“I haven’t seen you in years”), recognizes incongruities (“There’s something different about you”) and temporarily remembers routine details (“We parked in the third row”).

F. Striatum: Inside the brain. Remembers whether action is required, such as the necessity to duck away from a bee.

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To store one memory, the brain sets aside a network of thousands of brain cells, called neurons. Above, how simple memory works. Below, how neurons communicate electrically:

1) Above, a sending neuron transmits a voltage along its axon to the dendrites of the receiving neuron.

2) The gap, or synapse, between sending and receiving neurons, is so small it can be seen only with an electron microscope. Electrical impulses are sent by squirting a chemical called a neurotransmitter across the synapse.

3) If enough neurotransmitter sticks to the receptor, the receptor opens. Brain fluid and its sodium ions flow through the channel. When enough ions enter through enough receptors, the receiving neuron fires its electrical impulse to another neuron down the network. This occurs throughout the memory network, recalling the memory as quickly as one-fifth of a second.

Getting a Quick Reaction

The memory system is so finely tuned that sensing an object, sound or circumstance can make you move faster than you can think.

1) You see a multicolored, long coiled object.

2) Visual cortex queries the neocortex (“Have you seen anything like this?”) and the neocortex replies (“It looks like a snake”).

3) Hippocampus remembers a snake isn’t normally there.

4) Amygdala remembers you hate snakes and switches on fear.

5) Striatum remembers that when startled by a snake, you are supposed to jump back. This message is relayed to your muscles, and you jump. Sources: Center for the Neurobiology of Learning and Memory, UC Irvine; Researched by STEVE EMMONS / Los Angeles Times