Memory: Blood simple?
While Suzuki measured electrical activity in hippocampus nerve cells, you can also measure brain activity with an MRI -- a magnetic resonance imager. Here's the drill -- active areas of the brain, like those absorbed in learning American history or French -- need lots of oxygen, and plenty of the red stuff.

Inactive areas, say those "absorbed" in watching a sitcom rerun, need less blood. Because the MRI is harmless, it can be used with the mammal that most fascinates neuroscientists -- the human being.

Using a highly accurate MRI, Susan Bookheimer, of the department of psychiatry and biobehavioral sciences at the University of California-Los Angeles, and colleagues watched while 10 people learned to associate names with faces. That's a classic "declarative memory" task that's should call for heavy lifting in the hippocampus.

Instead of looking at just the hippocampus, Bookheimer also measured some nearby brain structures (they're called the medial temporal lobe, or MTL, if you insist), that also "do memory."

Together, she found that specific parts of the MTL were devoted to either input (learning) or output (memory retrieval).

The hippocampus and nearby memory structures. In this averaged view, red indicates learning, blue indicates recall, and purple indicates regions with both functions. Courtesy Susan Bookheimer, UCLA

Cerebral cinnamon roll
Unfortunately for neuroscientists, the hippocampus is coiled in on itself like a cinnamon bun. If you were to "study" a slice of cinnamon bun, you would get a confusing blend of butter, cinnamon and dough, says Bookheimer, "but if you unroll the bun, you'll see, oh yes, the cinnamon is here, the butter is there."

Ditto for the hippocampus.

Instead of doing the obvious -- getting her hands full of cinnamon and butter -- Bookheimer digitally flattened the medial temporal lobe in a computer, and then found that three areas, the cornus ammonis 2 and 3 (CA2 and CA3), and the dentate gyrus, play a role in encoding, or establishing, memories.

Tellingly, these three bits of brain reside on the input circuits of the MTL -- where nerve impulses enter the hippocampus.

The binding of memory
As Bookheimer describes it, the job of these input regions is to link separate neural impulses. "The essential thing about the hippocampus is that it allows you to bind an association together in novel ways," she says. "Faces and names are an arbitrary association... . What the hippocampus is likely doing is binding that information together, holding the face with the name," then storing the visual memory in one place, and the verbal memory in another.

To strengthen the link, some circuits in the medial temporal lobe simply echo the linked information back at themselves: "His name is Fred," "His name is Fred."...

The upshot of all this linkage, Bookheimer says, is "like a reference in a card catalog. You look up information for that face, and it sends you to the name."

After the association is nailed down, especially after it has been successfully retrieved even once, the input regions slack off, Bookheimer says, since their activity level is determined by "how much information is being bound together at that moment."

Like a student who's just passed finals, this bit of brain seems to figure, "We've learned this stuff already. Time to party." (We hate to be killjoys, but Bookheimer mentions that, "Hippocampal neurons are especially sensitive to drugs and alcohol, which can kill off all that hard work of binding connections in a single shot.")

Practically speaking
Alongside the basic research on memory, neuroscientists have learned lessons that might help anyone trying to learn French or the anatomy of the mouse brain. For starters, one successful retrieval increases your future chances of success, Bookheimer says. "If you just encode it but don't practice retrieval, that's less associated with success. So don't just study, but ask questions. Use flash cards that require you to generate the answer based on the cue."

A second lesson is that more associations make stronger memories. If you try to link the French noun "cycliste" with "bike rider," you have only one association to remember, and "when the hippocampus goes to rebuild it, it will have only what you initially encoded," Bookheimer says.

Instead, try adding some associations: "I watched cyclist Lance Armstrong win the big race," "I cycled on a black Schwinn one-speed as a kid," and "I love to cycle down a long hill on two wheels."

This technique provides plenty of memorable associations, and it's especially good since it includes verbal, visual, muscular, and spatial memories, giving multiple ways to retrieve the pesky definition.

Those tactics, Bookheimer says, will help the little cinnamon roll in your noggin decipher the world around you. "One role of the hippocampus is to reform memories given partial clues," she says. "The more associations, the more clues you have, the better you will be at finding a clue that is effective."

What happens to individual neurons when we learn?

There are 1 2 3 4 5 pages in this feature.
Bibliography | Credits | Feedback | Search

©2003, University of Wisconsin, Board of Regents.