For the first time, a single gene has been linked to the learning process.
Researchers from the Massachusetts Institute of Technology and the Salk Institute in San Diego are to report in today's issue of the journal Science that their findings with mice provide sharp insight into the biochemical process by which the brain learns, particularly into how connections between individual brain cells are strengthened to form memories.
In the study, mice missing the gene for a key brain enzyme were unable to remember how to work their way through a maze. Though this is the first such gene found, the researchers believe there may be others involved in the process.
While the research is directed simply toward a better understanding of the brain, it may also have implications for human health. Epilepsy, chronic anxiety and damage to brain cells during a stroke are all thought to be caused by aberrations in the same basic process involved in learning, and the discovery may lead to novel ways to treat or prevent them.
"The paper is particularly significant in two ways," said Dr. Paul Greengard, a neuroscientist at Rockefeller University in New York City. It is important because it implicates one particular gene in learning and memory, he said. Also, "the ability to remove a single gene from the mice also opens up a whole new way of studying learning and memory."
"It's an incredibly fascinating approach," said neuroscientist Ron Davis of the Cold Spring Harbor laboratory in New York. "Genetics is going to be the best way" to study the biology of learning, he added.
The researchers are studying a learning process called long-term potentiation or LTP. In this process, thoughts or actions electrically "excite" specific brain cells, causing strengthening of the connections between the cells. These strengthened connections become stored memories. Indirect studies have suggested that a group of enzymes called kinases play a key role in strengthening those connections and thereby forming memories.
MIT molecular biologists Susumu Tonegawa and Alcino J. Silva used genetic engineering techniques to remove or "knock out" the gene for one of these enzymes, called CAM kinase, from mouse embryos. The mice then matured normally, but they exhibited learning problems.
The findings could promote research on a phenomenon called called excitotoxicity, which is the cause of brain-cell death in epilepsy, stroke and head trauma. The biochemical mechanisms LTP and excitotoxicity are apparently identical, said Dr. Charles Stevens, a Salk neurobiologist.