I Cannot Remember a Thing. Am I Losing Brain Cells?

The real reason for knowledge decline in the aging brain is now thought to be small changes in the structure, function and communication between brain cells rather than their complete loss. Neurons typically have many branches allowing for multiple points of connection with other neurons to form complex circuits. But as we age, scientists have found that neurons lose a lot of their branches and together with specific chemical changes in the neurons, these subtle structural changes alter their functioning. Certain regions of the brain are more susceptible to these age related changes than others leading to a decline in some mental faculties but not others. But the good news is that many studies have shown that the brain remains capable of regrowth and learning.

It wasn’t until 1998, that researchers led by Peter Eriksson of the Sahlgrenska University Hospital in G`teborg, Sweden and Fred H. Gage of the Salk Institute in San Diego [1], California first found evidence of new neurons being produced in the brains of adult humans as old as 72 years of age! Research over the last decade has produced growing evidence that the adult human brain in fact creates new neurons throughout our lifespan, overturning decades of dogma that the cells you have at birth are about all you’ll ever have, and a neuron lost is lost forever.

This “neurogenesis”, or creation of new neurons, arises from neural stem cells that exist in the adult human brain. The most active area of neurogenesis is the hippocampus, a region deep within the brain involved in learning and memory. Research shows that the hippocampus produces thousands of new cells each day. Although many die within weeks of their birth, recent findings show that many of these new neurons survive and integrate themselves into the working brain, suggesting the potential for a self-healing brain. To live and become part of the working brain, a new neuron needs connections with other neurons. Without these connections, neurons wither and die.

Several factors can determine whether a new neuron integrates into the existing brain circuitry. One of these is learning and another one we know of is exercise.

Recent animal studies have shown a correlation between learning and new neurons surviving in the hippocampus. After teaching rodents a variety of tasks that engaged a range of brain areas, scientists found that, generally, the more the animal learned, the more neurons survived in the hippocampus. Cells that were born before the learning experience were more likely to survive to become neurons, but only if the animals actually learned. The increase in survival occurred with tasks that depended on the hippocampus as well as those that required significant effort to learn [2].

Everybody knows that exercise is good for your heart, but in recent years, compelling evidence has shown that exercise is also good for your brain. Experiments have found that mice that used a running wheel had about twice as many new hippocampal neurons as mice that didn’t exercise. Learning may still be necessary to preserve them, however [3].


  1. Peter S. Eriksson et al. (1998). Neurogenesis in the Adult Human Hippocampus. Nature Medicine (4): 1313-1317.
  2. Waddell J, Shors TJ. (2008) Neurogenesis, learning and associative strength. Eur J Neurosci. 27(11):3020-8.
  3. van Praag H, Shubert T, Zhao C, Gage FH. (2005) Exercise enhances learning and hippocampal neurogenesis in aged mice. J Neurosci.25:8680–8685.