Changes in the Aging Brain

"By the time you're eighty years old you've learned everything. You only have to remember it."
– George Burns (1896-1996)
We are all aging. It is estimated that by the year 2050, 30% of the world’s population will be over 65 years of age, and we might be a part of that demographic at that point. It is clear that the incidence of many of the major disorders, such as Alzheimer's disease, increase with age and that their etiology may involve lifestyle determinants, environmental and genetic factors, and aging. Have you ever wondered what changes occur inside your brain as you age?

Lord of the Rings: The Fellowship of the Ring. New Line Cinemas.
We are born with most of the 100 billion neurons that we’ll have for the duration of our lives. During childhood, about 85% of the brain development occurs, including intellect, personality, and motor and social skills1. However, a child’s brain has twice as many synapses as an adult’s brain. In a process called pruning, the neural connections that are used and reinforced most often, like those used for language, are strengthened, while the ones that are not heavily utilized die out (that’s a primary reason why parents are encouraged to repeat certain activities, like reading books, with their kids every day). During our teen years, the brain reaches its adult weight of about three pounds, but the wiring is certainly still a work in progress. This is why scientists believe that teenagers generally tend to be more reckless, irrational and irritable given the cacophony of construction going on inside the adolescent brain. The brain’s power peaks at age 22. After that, the brain’s performance slowly begins to decline.
That the brain changes with increasing chronological age is clear, however, less clear is the rate of change, the biological age of the brain, and the processes involved. Although structural changes do not occur to the same extent in all parts of the brain2, it has been widely found that the total volume of the brain and/or its weight declines with age at a rate of around 5% per decade after age 403. Most of these changes occur in the grey matter and stem from neuronal cell death4. It has also been suggested that a decline in neuronal volume rather than quantity contributes to the changes in an aging brain. Additionally, there may be changes in dendritic synapses or loss of synaptic plasticity (the ability of synapses to strengthen or weaken their activity). Deterioration of white matter in the aging brain also plays a role. The myelin sheath surrounding the fibers of the neurons begins to degrade after the age of 40, and it is theorized that the length of myelinated axons is greatly reduced, up to almost 50% by the time we are 65. Further changes in the brain may be related to sex with different areas being more affected in men than women5.

Futurama. Fox Television.
The most noticeable changes associated with aging is that of memory. Memory function is of different types, and some types of memory stay the same over age (such as semantic memory) whereas other types of memory decline over age (such as episodic memory). An example of semantic memory would be understanding the concept that clocks are used to tell the time, and an example of episodic memory would be remembering where you left your car in the parking lot. There have been studies investigating different types of memory in aging using neuropsychological testing and neuroimaging and the most consistent finding of these studies was that the brain activity tends to be less in older adults than in younger adults6. Besides reduced cerebral activity, other changes in the brain include reduction in cerebral blood flow, reduced vascular density, intra/extracellular changes, and changes in tissue organization.
The neurotransmitters most often associated with aging are dopamine and serotonin. It is known that levels of these neurotransmitters, as well as brain-derived neurotrophic factor (BDNF), decline by around 10% per decade from early adulthood and these have been implicated with declines in cognitive and motor performance. Other factors that have been implicated in the aging brain include reduction in synapses and receptors, reduced binding of neurotransmitters to receptors, calcium dysregulation, mitochondrial dysfunction, production of reactive oxygen species, and neuroinflammation that can lead to a build-up of deposits in areas like the hippocampus causing Alzheimer’s disease.

Spongebob Squarepants. Nickelodeon Studios.
Even the healthiest amongst us cannot stop our brains from changing with time. That being said, it’s not all bad news. Scientists now believe that maintaining a healthy life, both physically and mentally, may be the best defense against the changes of an aging brain. Activities such as participating in social and community activities, physical activities and exercise, reading, listening to music, working on a hobby, eating a healthy diet, and reducing stress can all improve mood and memory function. So the process of aging depends heavily on the individual, and I can’t think of a better example than that of Stanley Kunitz who, at the age of 95, was named Poet Laureate of the United States. Until he died at the age of 100, Kunitz was still writing new poems, still reading to live audiences, and he stood as an inspiring example of the brain's ability to stay vital in the final years of our lives. Perhaps the aging brain is far more resilient than what we give it credit for! Let us know your thoughts by contacting us at tech@biolegend.com.

The Lion King. Disney Studios.
Contributed by Mohar Chattopadhyay, PhD.
References:
  1. Brain development and early learning
  2. Brain aging in the new millenium
  3. Structural brain changes in aging: courses, causes and cognitive consequences
  4. Aging of the brain
  5. Sex differences in human brain morphometry and metabolism: an in vivo quantitative magnetic resonance imaging and positron emission tomography study on the effect of aging
  6. Cognitive neuroscience of aging: contributions of functional neuroimaging
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