Don’t You Forget About Me

You meet someone and later you’re trying to remember his or her name. Sound familiar? Neuroscientists call it associative memory.

“It’s a critical form of memory because it really defines us as individuals,” says Wendy Suzuki, assistant professor of neuroscience and psychology at the Center for Neural Science at New York University. “Our memories for the facts that we’ve learned and the events that we’ve experienced in our lives is really what makes us who we are. So that’s why it’s the focus of so much cognitive neuroscience research today.” Associative memory is, for example, the ability to learn the relationship between unrelated items, such as the name of someone you just met and that person’s face.

“We specifically studied the situation where you meet somebody for the first time and you learn that person’s name,” says Suzuki. “And you may repeat it several times and by the end of the conversation, you are able to recall that person’s name and evoke that person’s name if somebody reminds you about the situation.”

Suzuki and her team studied two adult rhesus monkeys playing a memory-based video game in which an image pops up on the computer screen with four targets—white dots—superimposed on it. The monkeys’ task was to learn which target on which image was associated with a reward (a drop of their favorite fruit juice).

While the monkeys played the game, called a location-scene association, the researchers used extremely thin electrodes to monitor the electrical activity of cells in the monkeys’ brains, specifically in the hippocampus, the banana-shaped area of the brain that’s a hub for learning and memory.

One line shows the monkey's learning curve, the other shows the activity level of nerve cells in the hippocampus.

“We found hippocampal cells change their activity dramatically, directly in parallel with the animal’s behavioral learning curve,” says Suzuki, who published her research in the June 6, 2003 issue of Science. “So, as the animal got better and better at performing this location-scene association, some cells increase their activity dramatically, or decrease their activity dramatically, but both in parallel with the animal’s learning. That allows us to conclude that these hippocampal cells are very involved in the initial formation of these new memories that the animals are forming each day. It was kind of like being able to watch the formation, or the birth of a new memory.”

Suzuki and her team were also interested in those cells that not only changed their activity when learning occurred, but also sustained that change during the entire recording session. “That suggests that these cells may be part of a longer term circuit that underlies the long term memories themselves,” says Suzuki.

Knowing how the normal brain works is an important key towards understanding and treating memory-related diseases like Alzheimer’s. “To be able to go in and intervene in devastating situations like Alzheimer’s, where the hippocampus is full of plaques and tangles and the person has very, very poor memory, you need to understand how the hippocampus works normally,” says Suzuki. “What is the normal function? What is the normal neural code that allows the hippocampus to form new memories or to help you retain new memories? That’s what our studies help us understand, that basic understanding of what the hippocampus does normally. Unless you understand that, there’s no way, there’s no hope of intervening in a sophisticated way into the functions of the hippocampus.”

Suzuki says that although they studied the activity of the hippocampal cells, there are other strongly inter-connected brain areas that are also involved in learning and memory. The team plans to further study how those areas may also be “contributing to the formation of new associations.”

Funding for this research came from the National Institutes of Health, the National Institute on Drug Abuse, the McKnight Foundation and the John Merck Fund.