The Aging Brain
Today, we will be discussing healthy and abnormal aging of the brain, as well as adaptive mechanisms we can use to our advantage to help improve longevity of our brains.
Normal Brain Aging
In a healthy human, the volume of the brain shrinks by 5% per decade after the age of 40, accelerating after 70 years of age. In general, the volume loss of the brain is caused due to neurons dying with age.
This decline is greater in the prefrontal cortex (executive functioning, working memory), than the basal ganglia (connections with body and other regions in the brain), than the temporal lobe (memory, fear and emotional regulation, auditory processing), than other regions. The levels of dopamine and serotonin also decline with aging, and there is a decreased blood flow in the brain. The only aspect of brain function that increases with age is verbal knowledge, which is why people become wiser with age, retaining more knowledge.
Mild Cognitive Impairment (MCI)
MCI is a clinical diagnosis that can be temporary or permanent, falling between dementia and healthy aging. This means that a person can still function and continue daily activities, but there is some cognitive difficulty like memory problems. 12-18% over the age of 60 get MCI, and 5-6% of these patients develop dementia per year.
Metabolism and the Aging Brain
Metabolism refers to a series of chemical reactions that allow the body to turn food into energy, occurring inside of cells in the body. There are many metabolic adaptations that happen in the brain with aging.
Back in the day, people had to find food to survive so their brains evolved to become used to this food scarcity. Nowadays, we have food so easily available, and we spend most of our days sedentarily. This means the parts of our brain that are used to food scarcity are not used as much anymore because we eat more and exercise less. This causes a decline of the brain's structure and function as we age. We can exercise more, change our diets and use certain medicines to prevent or delay this.
When we eat less and exercise more, we increase fat metabolism (body changes fats we consume into energy) and ketone generation. Ketone bodies are found in the liver and they come from the fats we eat. When we fast, instead of relying on glucose (sugars), our body starts relying on ketone bodies. This stabilises neural networks, whereas glucose destabilises neural networks. A stabilised neural network means that aging becomes delayed and age-related brain diseases could be prevented. A similar process happens when we sleep, so increased sleep also shows metabolic adaptations in the aging brain.
These processes can have many positive effects. This includes creating mitochondria (the powerhouse of the cell that creates energy), repairing DNA, activating pathways in the brain that resist stress, and promote the recycling of old cells (autophagy).
Neural Networks and the Aging Brain
The brain can build neural resources over time that can help with preventing or delaying the onset of brain dysfunction during aging. These are not clear, but education can help promote this reserve by increasing the density of neural connections in the hippocampus (for memory), and promoting connectivity between different regions of the brain.
The brain also has many compensatory behaviours for loss of function due to aging. Activations in different parts of the brain can compensate for brain regions dying by activating similar networks for multiple processes. An example is neural networks for focused attention being activated so that the aging brain can retain reading abilities. Being bilingual or multilingual also creates greater connectivity between various brain areas and preserving many brain structures with age. Furthermore, neural networks can be reorganised to maintain performance so even when one network starts to fail, another network can adapt to take over that role.
Cognitive training and social enhancement interventions do play a role in improving cognition and well-being with age. Having a large care network of different relationships such as friends and family always helps with fostering stronger positive neural networks.
Recent studies suggest that a reduced neural activity is an adaptive mechanism during aging to modulate stress resistance and resilience pathways. Many studies show that gene expression of excitatory synapses decreases in individuals with a longer healthspan and lifespan i.e. cognitively intact individuals. On the other hand, an increase in excitatory neurons predicts thinning of the cortex which could lead to MCI or Alzheimer's Disease.
This could be a reason why mindfulness activities help with longevity, by decreasing excitation in the brain. Partaking in activities that reduce stress and modulating resilience to stress with therapeutic techniques can thus help with longevity of the brain.
