The prevailing belief that new adult brain cells do not form has now been shown to be false. New neurons do indeed form, albeit at a much slower rate than in the developing child.
How New Neurons Form in the Adult Brain
Thousands of new neurons are formed daily in the hippocampus of the brain in a region known as the dentate gyrus. (Shors) The process begins with the division of neural stem cells in the hippocampus into two cells, one which remains a stem cell, while the other is destined to become a new neuron. The immature neuron then migrates to the dentate gyrus region, where the mature forming axons and dendrites. The maturing neuron also makes essential connections with the existing neural circuitry in the neighboring C3 region of the hippocampus in order to function. The maturation process for new neurons is about 14 days for laboratory rats, but can take up to 8 weeks for the human brain.
New Neuronal Growth in the Brain and Learning
The fact that new neurons form in the hippocampus is particularly significant, since this region of the brain is associated with learning and memory. Most of the newly formed neurons will die if learning does not take place. Research with rats has shown that there is a critical period for survival of neurons. This period is about one to two weeks after the stem cell begins to differentiate into neurons. Learning that takes prior to or after this time period will not save the neurons. Follow-up research with humans suggests the time period is considerably later, up to eight weeks after cell birth. The more difficult mental tasks seem to preserve the most neurons. Of course, learning takes place in a matter of seconds, so the newly formed neurons will not help in the current learning task. It appears the new neurons aid in the problem-solving skills of a previous learning task, so the neurons serve in a memory recall capacity.
Can the Concept of New Neuronal Growth in Adults Aid in Medical Conditions Involving Memory Loss?
Chemotherapy for cancer targets the cell division process required for new cell formation. Patients receiving chemotherapy often complain of difficulty learning and remembering things. It is now clear that the cognitive problems the patients are experiencing are due to lack of new neuronal growth.
There is considerable current interest in engaging elderly persons in activities that involve learning in order to stave off Alzheimer's disease. Although mental exercises are unlikely to prevent Alzheimer's, the patients may have a richer network of neural pathways, leading to a slower onset and progression of the disease. (Burling)
Boosting Brain Power of Adults
Many factors can influence the growth of new neurons. A positive outlook on life is important, as antidepressants have been shown to increase neuronal growth. Acute stress can block neurogenesis, while chronic stress can result is sustained suppression of neural growth. (Bioworld) Physical exercise is also important. Minimize the use of alcohol and nicotine as these substances can inhibit generation of neurons. Above all, adults should continue to engage in activities that stimulate learning, the more difficult the mental task the better.
References
BioWorld Today. "APA Annual Meeting 2007 New Neurons in Adult Brain Can Aid Memory, if Correctly Wired." 2007 May 29.
Burling, Stacey. "Brain Exercises May Help Keep Alzheimer's Away." Charleston Gazette. 2004 Feb 17.
Duan, Xin et al. "Development of Neural Stem Cell in the Adult Brain." Current Opinion in Neurobiology. 2008 Feb; 18(1): 108-115.
Shors, Tracey. "Saving New Brain Cells." Scientific American. 2009 March; 47-54.
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