The external signs of aging are hard to ignore – wrinkles, grey hair, and sagging skin. Although we can’t see it, the inside of our body is aging as well, and the brain – wrinkles, is not immune to this process. The brain is the boss of the body; it is the control centre that regulates our functions at both a conscious and unconscious level. As life expectancy is on the rise, understanding how the brain ages and what this means for quality of life becomes especially important.
Chronological aging causes widespread changes to the brain. The brain grows in size until the teen years, and during this time our intelligence, personality, and motor and social skills develop and become reinforced. Neural connections that are used often, such as those for language, are strengthened, whereas those that are not will die in the process of pruning. Neurons get bigger and work more efficiently, utilizing environmental input and stimuli to aid in the fine-tuning of our senses. The brain is adapting, learning, and forming new memories. It is an exciting time for the aging brain.
By our late twenties, the brain has reached its peak in terms of performance. It’s downhill for some skills, including our ability to think quickly and recall information. In our late 20s to early 30s, the brain starts to go through changes that can impair cognition. Regions thin and lose volume, myelin sheath surrounding axons deteriorates, neurotransmitter levels decline, and brain receptors fire slower. The number of neurons in the brain begins to decrease by our mid 30s, and memory starts to slip – another reason to finish up that graduate degree early! As we reach midlife, our reasoning skills decline; although, on the upside, other measures of intelligence such as moral decision-making, emotion control, and understanding of social situations, show improvement. However, by our 60s and beyond, the brain begins to shrink dramatically in size, and it becomes less efficient in accessing as well as adding knowledge.
It is estimated that 40% of people aged 65 and older will experience some form of memory loss. In the absence of disease this is referred to as age-associated memory impairment, a normal part of brain aging. Neurodegenerative diseases, on the other hand, are not a part of healthy brain aging, and sadly, aging is the greatest risk factor for developing one. These diseases are debilitating conditions that can affect different parts of the brain and are characterized by the progressive loss of function or structure of the nervous system, especially neurons. This causes problems with movement or cognition, termed ataxias or dementias, respectively. Dementias account for the largest proportion of neurodegenerative conditions, with Alzheimer’s disease (AD) being the most prevalent form of dementia.
As of 2017 there is an estimated 564,000 Canadians living with dementia, and an additional 25,000 new cases diagnosed yearly.
By 2031, this number is expected to rise to a staggering 937,000.
Alzheimer’s and other dementias are the 7th leading cause of death worldwide according to the World Health organization.
AD is associated with “plaques”, abnormal deposits of the β-amyloid protein between neurons, and “tangles”, twisted strands of the tau protein within neurons. Both become toxic at excessive levels and are the prime suspects of neuronal death in Alzheimer’s. Although the cause of AD is poorly understood, emerging evidence indicates that inflammation plays a critical role. It has previously been reported that the immune sensor, NLRP3, is activated in the brains of Alzheimer’s patients and contributes to the development of AD in a murine model. More interestingly, a recent study published in Nature demonstrated that inflammatory aggregates are released from activated immune cells in the brain, which then bind to β-amyloid and promote its aggregation, therefore contributing to the spreading of β-amyloid plaques. This directly links pro-inflammatory immune activation with the neurodegeneration observed in AD
As we age, the brain is changing, and even the healthiest among us cannot stop the aging process. Further research on the contributing factors underlying neurodegenerative diseases, such as inflammation, will help us in the battle against this inevitable process.
- Alzheimer Society Canada. “About dementia”. <http://alzheimer.ca/en/Home/About-dementia>.
- DZNE – German Center for Neurodegenerative Diseases. “Inflammation drives progression of Alzheimer’s: A molecular complex of the immune system promotes aberrant aggregation of proteins.” ScienceDaily. ScienceDaily, 20 December 2017. <www.sciencedaily.com/releases/2017/12/171220131656.htm>.
- Ruth Peters. “Ageing and the brain”. Postgraduate Medical Journal, 2006; 82: 84-88
- National Institute on Aging. “Basics of Alzheimer’s disease and dementia”. <https://www.nia.nih.gov/health/alzheimers/basics>
- Harvard Medical School. “How memory and thinking ability change with age”. <https://www.health.harvard.edu/mind-and-mood/how-memory-and-thinking-ability-change-with-age>.
- World Health Organization. “The top 10 causes of death”. <http://www.who.int/mediacentre/factsheets/fs310/en/>