What Is the Main Idea?

Some changes in cognitive function are considered to be a normal part of aging, but others can indicate the presence of disease, such as dementia. In the research article “Cognitive Activity Is Associated with Cognitive Function over Time in a Diverse Group of Older Adults, Independent of Baseline Biomarkers”, published in the journal Neuroepidemiology, the authors investigate whether there is a relationship between a person’s level of cognitive activity, biomarkers in their blood that can indicate Alzheimer’s disease or dementia, and changes in their cognitive function in older age.

What Else Can You Learn?

In this blog post, changes in cognitive function as we age are described. Cognitive reserve and different forms of dementia and also discussed.

How Does Cognitive Function Change as We Age?

The term “cognitive function” describes a combination of processes that take place in the brain that enable us to learn, manipulate information, remember, and make judgements based on experience, thinking, and information from the senses. These processes affect every aspect of life and our overall health, including how we form impressions about things, fill in gaps in knowledge, and interact with the world.

Some changes in cognitive function that are considered to be a normal part of the aging process include difficulties with multitasking and sustaining attention, and an overall slowing of the speed at which we think. The ability to “hold information in mind”, which means the ability to think about something without steady input about it from the outside world, also tends to decrease.

In contrast, skills like verbal reasoning and vocabulary tend to increase or stay the same as we get older. Changes in cognitive function that are considered a normal part of aging are usually subtle over time; however, some people experience major changes in cognitive function that may indicate the development of a neurodegenerative disease caused by abnormal changes in the brain, such as dementia. The term “neurodegenerative” means the degeneration or death of neurons, a type of cell that transmits messages from one part of the brain and nervous system to another.

What Is Dementia?

Dementia mainly occurs in people aged over 65 years and covers a range of conditions with different causes. For example, vascular dementia develops when blood flow to one or more areas in the brain is blocked or reduced, preventing cells from getting the oxygen and nutrients that they need to function properly.

In contrast, Alzheimer’s disease is believed to be caused by the abnormal functioning of two proteins called beta-amyloid and tau. In people with Alzheimer’s disease, beta-amyloid forms clumps called “plaques” on neurons that make it hard for them to stay healthy and communicate with each other, while abnormal forms of tau cling to other tau proteins inside neurons and form “tau tangles”. People with dementia often experience declines in cognitive function that affect their memory and other thinking skills like language, problem-solving, attention, and reasoning. Their behaviour, feelings, and relationships can also be affected, with significant effects on their daily lives.

What Did the Study Investigate?

It is well known that the extent to which a person engages in cognitive activity (mental tasks that require focus, reading, learning, creativity, memory, and/or reasoning) can affect their cognitive function as they age. There is strong evidence that people who are more cognitively active maintain higher levels of cognitive function over time than people who are less cognitively active, regardless of whether they develop a form of dementia. In other words, some brains keep working more efficiently than others despite them experiencing similar amounts of cognitive decline and/or damage. However, it remains unclear whether this is because cognitive activity directly benefits cognitive health or because people with declining cognitive function become less cognitively active.

What Is “Cognitive Reserve”?

The possibility that cognitive activity can positively affect our brain health relates to an idea called “cognitive reserve”. It suggests that people build up a reserve of cognitive abilities during their lives that can protect them against some of the cognitive decline that can happen as the result of ageing or the development of disease such as dementia. A person can increase their cognitive reserve through activities that engage their brain, such as learning a language or new skill, solving puzzles, and high levels of social interaction, particularly if the activities are novel and varied. Regular physical activity, not smoking, and a healthy diet are also important.

The idea of cognitive reserve is supported by research that has shown that the relationship between cognitive activity and function in older age is not affected by the degree of abnormal brain changes. In other words, two people with Alzheimer’s disease may have similar levels of beta-amyloid plaques and tau tangles in their brains, but may differ regarding the extent to which their cognitive function has declined. Equally, two people who seem to have the same level of cognitive function may differ regarding the extent of abnormal change that has happened in their brains.

What Role Do Biomarkers Play?

The authors investigated whether there is a relationship between the levels of three biomarkers in the blood that can be used to predict and stage some types of dementia, including Alzheimer’s disease, and the extent to which a person’s level of cognitive activity affects their cognitive function as they age. Biomarkers are measurable characteristics, such as molecules in the blood or changes in genes (mutations), that can indicate whether the body is working normally or a disease is present.

In this study, the authors measured the levels of three biomarkers in blood samples: total tau, neurofilament light chain (NfL),and glial fibrillary acidic protein (GFAP).

  • As already mentioned, tau tangles are a characteristic of Alzheimer’s disease, and high levels of total tau (both normal and abnormal forms of tau) in the blood have been reported to be associated with increased risk of cognitive impairment.
  • High levels of NfL in the blood have been linked to neurodegeneration and there is evidence that it may be possible to use levels of NfL in the blood to detect whether a person has dementia.
  • Levels of GFAP in the blood have been shown to be increased early on in the development of Alzheimer’s disease. This can be used to determine whether a person has Alzheimer’s disease or frontotemporal dementia which is a rarer type of dementia that affects the frontal and temporal lobes of the brain responsible for language, behavior, and emotions.

Who Participated in the Study?

The people who participated in the study were all aged 65 years or older, and one-third of the participants were randomly selected to give blood samples for biomarker testing at the start of the study. All of the participants reported how often they participated in cognitive activities that were judged to be common to older adults because they are not overly dependent on a person’s financial or social situation:

  • Watching television
  • Listening to the radio
  • Visiting a museum
  • Playing games or doing puzzles
  • Reading books
  • Reading magazines
  • Reading newspapers

Their cognitive function was also assessed at the start of the study and in 3-year cycles after that, using tests of short-term and immediate memory, perceptual speed, and language functioning.

What Did the Authors Find?

The authors of the study found that higher levels of cognitive activity were associated with better cognitive function not only at the start of the study, but also after an average of 6.4 years of follow-up when the authors made contact with participants at later, prearranged dates to check on progress. However, the levels of the blood biomarkers did not affect this relationship. In other words, the benefits of high levels of cognitive activity on cognitive function were not affected by the levels of tau, NfL, and GFAP in the blood, even when they were present at high levels.

These results lend weight to the idea of cognitive reserve and suggest that people who engage in enriching activities throughout their lives may enter old age with a higher level of cognitive function, which can delay or reduce any symptoms resulting from dementia or other neurodegenerative diseases from affecting their quality of life.

Take-Home Message

Ensuring that we are cognitively active before we reach our 60s (i.e., before the age at which the study’s participants were initially assessed) may benefit our brain health and cognitive function as we age. The fact that the authors of the study did not find a link between the blood biomarkers and cognitive activity over time also suggests that people benefit from enrichment activities throughout their lives, including in their later years.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available.

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