New Brain Cells Formed In Response To Learning
DATELINE: October 1999
Background: For many years scientists thought the number of brain cells at birth are all we ever have. As we age, it was believed, brain cells progressively die - and are never replaced. This idea was frequently offered as the reason behind such age-related problems as memory loss and senility. However, since there was no reliable method to actually observe brain cells over time, there was no way to confirm or deny this idea. About 30 years ago, a new tool was developed for brain research where brain cells - known as neurons - could be "tagged" with a chemical that allowed them to be tracked, and it was apparent that new neurons are born throughout the lifetimes of many creatures, including birds, monkeys, and, we now believe, human beings. But if this is true, why do many people still develop age-related problems of memory, thinking, and concentration?
Advance: Working with rats, scientists focused on a part of the brain known as the hippocampus, an area associated with learning and memory. The cells of the hippocampus were tagged, and the rats were then given a rigorous training period. The rats learned to navigate in spaces that were new to them, and to associate disconnected events. After the training period, the researchers observed a dramatic increase in the number of neurons in the hippocampus. And more than a week after the training sessions were over, the number of these cells still remained high. Beyond that, the researchers noticed there were more neurons in other areas of the brain as well - not just the hippocampus.
Implications: Neurons are not only born in response to the challenge of new learning, but live longer when learning is taking place. Learning, practicing, and remembering are all activities that seem to be linked not only to the development of new neurons, but with keeping those new cells healthy, functional, and living longer.
The clear demonstration that learning supports and promotes the health of brain cells is a remarkable addition to our scientific knowledge. After believing that the total number of neurons declined during life (and that how brains are used had no effect on the number of brain cells), we are now understanding that mental challenges impact the number of cells. This work confirms that the brain not only creates new cells throughout a lifetime, but those cells do better - live longer and stronger - if the brain they are a part of is actively learning.
Aside from giving medical research a strong foundation for understanding problems like learning disabilities and brain damage, this insight tells us that the brain actively responds to needs and demands - and, in fact, performs better in the face of challenges. In the largest sense, this research suggests that some aspects of age- or trauma-related memory loss are made worse by a lack of challenges for the brain. It may be that brains need new skills to master in order to maintain clearer thinking and sharper memory - for a longer period of time.
Gould E, Beylin A, Tanapat P, Reeves A, Shors TJ: Learning enhances adult neurogenesis in the hippocampal formation. Nature Neuroscience 2(3):260-265, 1999.
Gould E, Reeves A, Fallah M, Tanapat P, Gross CG, Fuchs E: Hippocampal neurogenesis in adult Old World primates. Proc Natl Acad Sci USA 96:5263-5267, 1999.
Source: National Institute of Mental Health
