Could brain-derived neurotrophic factor hold the key to maintaining an agile brain?
As we age, there is a depressingly inevitable decline in function. This deterioration is often most obvious in the body, but the brain also has a tendency to slow down.
But, cognitive decline is by no means guaranteed, and its speed differs drastically from person to person. Some individuals show virtually no change at all, while others show significant impairment.
The reasons for these neurological differences are unknown and considered well worth investigating. Ways to maintain a nimble mind in old age would be beneficial to all.
Of course, dementias, such as Alzheimer's, hasten the cognitive downturn attributed to advanced years, and researchers are determined to shine a light on any factors that might influence this process, too.
However, clues to the causal factors of mental decline with age are difficult to pin down; the brain is a complex organ, and aging is a multifaceted process.
Dr. Aron S. Buchman and his team at the Rush University Medical Center in Chicago, IL, set out to investigate the involvement of brain-derived neurotrophic factor (BDNF) in age-based cognitive deterioration.
Brain-derived neurotrophic factor
BDNF is a growth factor and can be found widely in both the brain and the peripheral nervous system. As the name implies, BDNF encourages the growth of new neurons and synapses, and supports existing neurons.
Much of the mammalian nervous system is laid down before birth, but parts of the brain retain the ability to grow new neurons in a process called neurogenesis. BDNF is one of the major players in this creation of new brain matter.
Research has shown that BDNF is essential in a number of important processes, including the maintenance of long-term memories.
Rats born without the ability to make BDNF have neural abnormalities and die soon after birth; conversely, if BDNF is injected into the lateral ventricle of an adult rat, new neurons sprout up in the striatum, septum, thalamus and hypothalamus.
BDNF's role in memory and the protection and development of neurons make it a prime candidate for investigations into the cognitive slump seen in many aging brains.
An answer to cognitive decline?
The present study used participants from the Rush Memory and Aging Project and the Religious Orders Study. In total 535 people, with an average age of 81, were followed until their deaths (average 6 years). Each year, various cognitive and memory skills were tested to chart the effects of age on mental agility.
After death, autopsies were carried out, and levels of the gene that codes for BDNF in the brain were measured. A neurologist checked the participants' medical records and rated whether they had dementia, mild cognitive impairment or no cognitive impairment.
The results showed that those with higher BDNF levels in the brain maintained cognitive function for longer. Individuals in the top 10% for BDNF showed a rate of decline 50% slower than those in the lowest 10%.
Alzheimer's disease produces so-called plaques and tangles in the brain. It is thought that the plaques and tangles negatively impact cognitive function. The study revealed that the effect of these markers on cognitive decline was reduced by 40% for individuals with the highest levels of BDNF.
Dr. Buchman says:
"This relationship was strongest among the people with the most signs of Alzheimer's disease pathology in their brains.
This suggests that a higher level of protein from BDNF gene expression may provide a buffer, or reserve for the brain and protect it against the effects of the plaques and tangles that form in the brain as a part of Alzheimer's disease."
The study is by no means definitive evidence of BDNF's role in mental decline. More work will need to be done. If it does turn out to be an important factor, strategies to increase brain levels of BDNF will be the next hurdle to jump.
Interestingly, there is some evidence that blood levels of BDNF are elevated during exercise. Although, at this stage, it is unclear how blood levels of BDNF impact levels in the brain. If there is a strong correlation, science might eventually show that something as simple as keeping active might stave off Alzheimer's.
Alzheimer's still holds many secrets; Medical News Today recently covered research into the role of brain inflammation in Alzheimer's.