Adult Neurogenesis and the Science of New Brain Cell Regeneration

Illustration of a human brain
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Conventional wisdom has long suggested that we cannot grow new brain cells; that we are born with all of the brain cells we will ever have and that once those gray cells expire, they're gone for good.

This belief was fueled, in part, by the fact that certain motor (movement) and cognitive (thought) functions tend to decline the older we get. But should this suggest that it's all downhill once we approach a certain age and that we have no choice but to wait for the inevitable decline?

Brain Cells and the Hippocampus

While the vast majority of our brain's cells are formed while we are in the womb, there are certain parts of the brain that continue to create new neural cells during infancy. Until recent decades, however, the brain’s limited capacity to regenerate triggered the belief that neurogenesis—the birth of new brain cells—ceased soon after this stage.

Recent research has shown otherwise and suggests, in fact, that at least one part of the brain continues to create new cells throughout a person's lifespan.

During the late 1990s, researchers at Rockefellers University in New York City conducted studies in which marmoset monkeys were injected with a tracer chemical that could differentiate between slow-dividing mature brain cells and fast-dividing new ones. What they found was that the hippocampus (a region of the brain associated with memories, learning, and emotions) continued to create new cells without the constraint of age or time.

Later studies using carbon-14 dating (which evaluate the age and process of cellular development) confirmed that cells in the hippocampus, while continually dying, were quickly replaced by new ones. It is only by the formation of these cells that the hippocampus is able to maintain its central functions.

What it also showed us is that the number of new cells, and the frequency by which they are created, begin to decline with age. With that being said, the rate of decline wasn't seen to be consistent and could vary significantly from subject to subject.

What Research Tells Us About the Birth of New Brain Cells

The research is considered important as is suggests that there are factors that can stimulate and inhibit the process of adult neurogenesis. It even hints at possible models for treating degenerative diseases, such as Alzheimer's and Parkinson's diseases, and even reversing damage caused by traumatic brain injury.

In some ways, the findings were neither surprising nor unexpected. Despite debate to the contrary, our very ability to form lasting memories and store information over long periods of time serves as evidence of this renewal process. Today, we recognize that adult neurogenesis is not only possible, but it is also a routine biological occurrence.

Factors That Influence Adult Neurogenesis

While we're still years away from pinpointing the mechanisms of adult neurogenesis, we are starting to identify certain factors that may "amp up" the process.

One of them is exercise. Early animal research conducted by scientists at the University of Chicago found that aerobic exercise led to both an increase in cell production in the hippocampus and increases in the amount of genetic information being encoded. What this tells us is that not only does the function of the brain improve, the cells themselves are better able to store information for learning and memory.

The findings were supported by research from the University of Pennsylvania which in 2010 reported that aerobic exercise among 120 older adults increased the actual size of the hippocampus by two percent and effectively reversed the aging-related cell loss by one to two years.

In addition to exercise, scientists have found that enriched learning environments can also contribute to the survival of old cells and production of new ones. In short, the more you exercise your brain, the more you will be able to maintain optimal brain function.

On the flip side, there are factors that directly undermine neurogenesis. Chief among these is age. We know, for example, that by the time many adults reach their 80s, as much as 20 percent of the neural connections in the hippocampus will be lost. Despite exercise and other stimuli, the development of new cells is rarely able to keep up with the loss of old ones.

Much of the focus of future research will likely aim to shift the balance between these gains and losses as we better identify both the external and internal factors that influence adult neurogenesis.

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