Neuro Science    

 

 

 

Ageing Brain

As we age, our brain undergoes a number of changes. One of the most notable changes is a decline in overall brain volume and a decrease in the number of neurons. Additionally, there may be a decline in the ability of the brain to repair itself, leading to an increased risk of damage and disease. There may also be a decline in cognitive function, such as memory, attention, and processing speed.

Putting this in a list, it would be listed as follows (NOTE : this is the list consolidated from many different sources and you may see some of the items are almost same but just a little bit different of wording. I didn't try to consolidate the list further to make it short because I think some repetition would not do any harm. On the contrary, a certain degree of repepition would help us to get familiar).

  • Decline in overall brain volume
  • Decrease in the number of neurons
  • Decline in the ability of the brain to repair itself
  • Increased risk of damage and disease
  • A decline in cognitive function - such as memory, attention, and processing speed
  • Be slower to find words and recall names
  • Find they have more problems with multitasking
  • Experience mild decreases in the ability to pay attention
  • Certain parts of the brain shrink, especially those important to learning and other complex mental activities.
  • In certain brain regions, communication between neurons (nerve cells) may not be as effective.
  • Blood flow in the brain may decrease.
  • Inflammation, which occurs when the body responds to an injury or disease, may increase.

There would be many additional examples of changes with age. I will talk about each of these items in more detail in this note.

NOTE : In the following details, there are description indicating the rate of changes in specific number. But those specific number would come from a limited amount of research result and may not be generalized or the number would show variations among different persons, sex and other factors. So just take it just as a ballpark figures (approximate number).

What are all the Changes that we will go through ?

As the human brain ages, it undergoes a series of intricate changes that affect its structure, function, and biochemical makeup. Understanding these changes can provide valuable insights into the aging process and its impact on cognitive health. The table below summarizes the key changes observed in the aging brain across various categories:

Category

Change

Description

Structural Changes

Brain Volume and Weight

The brain tends to shrink in volume and weight with age, with the most pronounced changes occurring in the frontal cortex and hippocampus, areas involved in higher cognitive functions and memory.

Neuron Loss

There is a gradual loss of neurons in certain brain regions, although this varies by region and individual.

White Matter Changes

White matter, which consists of nerve fibers, often shows signs of degeneration, including reduced density and the presence of white matter lesions.

Cerebral Atrophy

Overall, there is a decrease in the size of various brain structures, leading to cerebral atrophy, which is more pronounced in certain areas like the prefrontal cortex.

Functional Changes

Cognitive Decline

Aging is associated with declines in cognitive functions such as memory, attention, processing speed, and executive functions. These changes are not uniform and vary among individuals.

Neurotransmitter Changes

Levels of neurotransmitters like dopamine, serotonin, and acetylcholine decrease with age, affecting mood, memory, and cognition.

Plasticity Reduction

The brainís ability to reorganize and form new connections, known as neuroplasticity, diminishes with age, impacting learning and memory.

Biochemical Changes

Oxidative Stress

Increased oxidative stress, due to the accumulation of free radicals, leads to cellular damage and contributes to aging and neurodegenerative diseases.

Inflammation

Chronic low-grade inflammation, often referred to as "inflammaging," becomes more prevalent, affecting brain function and increasing the risk of neurodegenerative diseases.

Protein Accumulation

The buildup of misfolded proteins, such as amyloid-beta and tau, is common in aging brains and is strongly associated with Alzheimer's disease.

Cellular and Molecular Changes

Mitochondrial Dysfunction

Mitochondria, the energy-producing organelles in cells, become less efficient with age, leading to decreased energy production and increased susceptibility to damage.

DNA Damage

Accumulation of DNA damage and reduced efficiency of repair mechanisms contribute to cellular aging and the decline of brain function.

Telomere Shortening

Telomeres, the protective caps on the ends of chromosomes, shorten with age, which can trigger cellular senescence and reduce the regenerative capacity of brain cells.

Structural Change Snapshot

The human brain, a marvel of complexity, embarks on a lifelong journey of subtle transformation. Through the lens of MRI technology, we can witness the fascinating changes that occur as we age. While often associated with growth and development in our early years, the brain's evolution continues well into adulthood and beyond. These MRI images offer a visual narrative of this ongoing journey, highlighting the nuanced shifts in brain structure that accompany the aging process. Join us as we explore the intricate details revealed by these scans, shedding light on the remarkable adaptability and resilience of the human brain throughout life's later chapters.

Following brain image shows an example of structural change in our brain as we ages.

Image Source : Brain Morphometry and Cognitive Performance in Normal Brain Aging: Age- and Sex-Related Structural and Functional Changes

Key observations on this image can be summarized as :

  • Decreased brain volume: The overall size of the brain decreases with age. This is most noticeable in the older adult brain (D) compared to the adolescent brain (A).
  • Enlarged ventricles: The ventricles (fluid-filled spaces) within the brain enlarge with age. This is particularly evident in the axial (bottom row) views.

These changes are normal parts of aging and can be attributed to various factors, including:

  • Atrophy: The gradual loss of neurons and their connections.
  • Vascular changes: Reduced blood flow and changes in blood vessels within the brain.
  • Myelin loss: Degradation of the protective myelin sheath around nerve fibers.

While these changes are a natural part of aging, it's important to note that they can also be associated with cognitive decline and an increased risk of neurological conditions. Understanding the typical progression of brain changes throughout life is crucial for identifying deviations from the norm, which may warrant further investigation or intervention.

Changes in Overall Brain Volume

The volume of the brain and/or its weight declines with age at a rate of around 5% per decade after age 40 with the actual rate of decline possibly increasing with age particularly over age 70.

The exaxt mechanism behind this volume reduction is not clearly known. Some of hypothesis are as follows :

  • due to neural cell death
  • due to the decline in neuronal volume (e.g, decrease of the volume of support cells (glia cells)
  • due to changes in dendritic arbour, spines and synapses
  • due to increase in the amount of water in the brain, leading to an expansion of the brain's ventricles and a decrease in overall brain volume

NOTE : It is unlikely to have a single reason for the volume reduction. It is more likely that multiple factors works simulteneously or those factors may varies with person and sex.

Changes in Cortical Density

As we age, there are changes in the density of the brain's cortex, which is the outer layer of the brain that is responsible for many of our cognitive functions such as perception, attention, and memory.

One of the most well-known changes in cortical density with aging is a decrease in gray matter volume. Gray matter is composed mainly of nerve cells and their connections, and its volume decreases with age in many brain regions, particularly in the prefrontal cortex, temporal lobes, and parietal lobes. This decrease in gray matter volume is thought to be due to a loss of nerve cells and synapses (connections between nerve cells) as well as changes in the support cells called glia.

A study that used magnetic resonance imaging (MRI) found that the cortical thickness of the brain decreases by about 0.5% to 1% per year after the age of 40. Another study using MRI found that the cortical thickness decreases by about 0.02 mm per year between the ages of 20 to 80.

Changes in White matter

White matter typically deteriorates with age. This can lead to a decline in cognitive function, including problems with memory, attention, and decision making. The most common age-related changes in white matter include the loss of myelin.

White matter is composed mainly of the long fibers (myelinated nerve fibers) that connect different brain regions, and its volume increases with age. The increase in white matter volume is thought to be due to the accumulation of myelin, a fatty substance that surrounds the fibers and helps to speed up the transmission of signals. It is believed that slowing down processing and reducing cognitive function is related to the myelin shrinks.

It is believed that the myelin sheath start deteriorating after around the age of 40 even in normal ageing and deteriorate more significantly in the 60s and beyond.

Some study using MRI scans, found that the white matter volume in the brain decreases by about 0.2% per year for adults between the ages of 30 to 90. Another study, using Diffusion Tensor Imaging (DTI) found that the fractional anisotropy (FA) of white matter decreases by about 0.1% per year for adults between the ages of 20 to 80.

Changes in Neurotransmitters

With ageing, the brain begins to produce different levels of chemicals that affect neurotransmitters and protein production, ultimately leading to a decline in cognitive function.

One of the most well-known changes in neurotransmitters with aging is a decline in the level of acetylcholine. Acetylcholine is a neurotransmitter that is involved in memory, attention, and learning. A decline in acetylcholine levels is thought to contribute to age-related memory decline and the development of Alzheimer's disease.

Another change in neurotransmitters with aging is a decline in the level of dopamine. Dopamine is a neurotransmitter that is involved in motivation, reward, and movement control. A decline in dopamine levels is thought to contribute to age-related changes in motor function, such as Parkinson's disease, and mood disorders, such as depression.

There are also changes in the balance of other neurotransmitters such as norepinephrine, serotonin and GABA, which can also have impact on cognitive function and mood regulation.

Which part of the brain shrinks the most ?

Brain changes do not occur to the same extent in all brain regions.

The frontal lobe and hippocampus shrink more than other areas while brain volume decreases overall with age and we would see some degree of shrink in temporal lobes.

The area of major brain changes seems to vary in men and women. frontal and temporal lobes most affected in men compared with the hippocampus and parietal lobes in women

The rate of reduction in brain volume may increase with age particularly over 70

You may correlate these shrink of the parts of the brain with common behavioral changes that are commonly observed among elderly persons.

Behavioral changes associated with the shrinkgage in Hippocampus

  • Difficulty with memory recall: older adults may have trouble remembering recently learned information, such as names, dates, or appointments. They may also have difficulty with spatial memory, such as getting lost in familiar places or having trouble remembering the layout of their own home.
  • Difficulty with spatial navigation: older adults may have trouble navigating new environments, such as finding their way around a mall or a new neighborhood. They may also have trouble remembering the route they took to get somewhere and retracing their steps.
  • Difficulty with pattern recognition: older adults may have trouble recognizing patterns in visual or auditory information, such as recognizing familiar faces or voices, or being able to distinguish between similar-sounding words.
  • Difficulty with mental flexibility: older adults may have trouble shifting their attention between tasks or adapting to changes in their environment. They may also have trouble with mental flexibility, such as being able to change their plans or adjust to unexpected events.

Behavioral changes associated with the shrinkgage in Prefrontal Cortex

  • Difficulty with decision making: elderly adults may have trouble making decisions, particularly those that require weighing the pros and cons of different options. They may also have trouble with impulse control, acting on impulse rather than considering the consequences of their actions.
  • Difficulty with planning: elderly adults may have trouble organizing their thoughts and activities, and may have trouble setting and achieving goals. They may also have trouble with time management, struggling to prioritize tasks and manage their time effectively.
  • Difficulty with problem solving: elderly adults may have trouble solving problems, particularly those that require creative thinking or abstract reasoning. They may also have trouble with mental flexibility, struggling to adapt to new information or changing situations.
  • Difficulty with attention and focus: elderly adults may have trouble focusing and maintaining attention, particularly when faced with distractions or when asked to multitask. They may also have trouble with working memory, struggling to hold onto and manipulate information in their minds.

Behavioral changes associated with the shrinkgage in Temporal Lobe

  • Difficulty with language processing: older adults may have trouble with language comprehension, particularly with understanding complex sentences or figurative language. They may also have trouble with word retrieval, struggling to find the right word to use in a sentence, or with naming objects or people.
  • Difficulty with memory: older adults may have difficulty with memory, particularly with recall of past events. They may also have difficulty with semantic memory, which is the memory of facts and general knowledge.
  • Difficulty with auditory processing: older adults may have difficulty with processing auditory information, such as speech and music, particularly in noisy environments. They may also have difficulty with distinguishing between similar-sounding words or recognizing familiar voices.
  • Difficulty with face recognition: older adults may have difficulty recognizing familiar faces, particularly if they are seen out of context or if there are changes in the person's appearance.
NOTE : you may notice that the some of the difficulties listed here are similar (or same) as the one listed as in the case of hippocampus shrinkage. It is because Hippocampus itself is embedded deep inside of temporal lobe. That is, temporal lobe shrinkage may lead to Hippocampus functionality changes as well

Personal Experiences

Here I want to list some of the personal experiences about myself which seems to be related to againg brain.

  • Sometimes I have difficulties in remembering correct words (sometimes technical terminology in my area of work, sometimes the words in daily life.. like sphagettie etc). Interesting thing is that usually the correct words pops up in a few minunites or a few tens of minutes). I think I start having this problem in the late 50s (at around 58).
  • Sometimes I have difficulties in getting back to what I was about to do. For example, I was about to do 'A'.. but I had to do 'B' first due to urgent call for a few minute and then I have difficulties with recalling what I was about to do before.

Reference

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