At around 3 pounds in weight, the human brain is a staggering feat of engineering with around 100 billion neurons interconnected via trillions of synapses.
Throughout our lifetime our brain changes more than any other part of our body. From the moment the brain begins to develop in the third week of gestation to old age, its complex structures and functions are changing, networks and pathways connecting and severing.
During the first few years of life, a child's brain forms more than 1 million new neural connections every second. The size of the brain increases fourfold in the preschool period and by age 6 reaches around 90 percent of adult volume.
The frontal lobes - the area of the brain responsible for executive functions, such as planning, working memory, and impulse control - are among the last areas of the brain to mature, and they may not be fully developed until 35 years of age.
Normal brain aging
As we age, all our body systems gradually decline - including the brain. "Slips of the mind" are associated with getting older. People often experienced those same slight memory lapses in their 20s and yet did not give it a second thought.
Older individuals often become anxious about memory slips due to the link between impaired memory and Alzheimer's disease. However, Alzheimer's and other dementias are not a part of the normal aging process.
Common memory changes that are associated with normal aging include:
- Difficulty learning something new: Committing new information to memory can take longer.
- Multitasking: Slowed processing can make processing and planning parallel tasks more difficult.
- Recalling names and numbers: Strategic memory that helps memory of names and numbers begins to decline at age 20.
- Remembering appointments: Without cues to recall the information, appointments can be put safely in storage and then not accessed unless the memory is jogged.
While some studies show that one third of older people struggle with declarative memory (memories of facts or events that have been stored and can be retrieved), other studies indicate that one fifth of 70-year-olds perform cognitive tests just as well as their 20-year-old counterparts.
Scientists are currently piecing together sections of the giant puzzle of brain research to determine how the brain subtly alters over time to cause these changes.
General changes that are thought to occur during brain aging include:
- Brain mass: Shrinkage in the frontal lobe and hippocampus - areas involved in higher cognitive function and encoding new memories - starting around the age of 60 or 70 years.
- Cortical density: Thinning of the outer-ridged surface of the brain due to declining synaptic connections. Fewer connections may contribute to slower cognitive processing.
- White matter: White matter consists of myelinated nerve fibers that are bundled into tracts and carry nerve signals between brains cells. Myelin is thought to shrink with age, and as a result, slow processing and reduce cognitive function.
- Neurotransmitter systems: Researchers suggest that the brain generates less chemical messengers with aging, and it is this decrease in dopamine, acetylcholine, serotonin, and norepinephrine activity that may play a role in declining cognition and memory and increased depression.
In understanding the neural basis of cognitive decline, researchers can uncover which therapies or strategies may help slow or prevent brain deterioration.
Recent discoveries in brain aging
Several brain studies are ongoing to solve the brain-aging conundrum, and discoveries are being frequently made.
"Our research shows that the number of hypothalamic neural stem cells naturally declines over the life of the animal, and this decline accelerates aging," says Dr. Dongsheng Cai, Ph.D., professor of molecular pharmacology at Einstein. "But we also found that the effects of this loss are not irreversible. By replenishing these stem cells or the molecules they produce, it's possible to slow and even reverse various aspects of aging throughout the body."
Injecting hypothalamic stem cells into the brains of normal old mice and middle-aged mice, whose stem cells had been destroyed, slowed or reversed measures of aging. The researchers say this is a first step toward slowing the aging process and potentially treated age-related diseases.
"SuperAgers" are a rare group of individuals over the age of 80 years who have memories as sharp as healthy people decades younger.
Research by Northwestern University Feinberg School of Medicine in Chicago, IL, compared SuperAgers with a control group of same-age individuals. They found that the brains of SuperAgers shrink at a slower rate than their age-matched peers, which results in a greater resistance to the typical memory loss observed with age, thus revealing that age-related cognitive decline is not inevitable.
"We found that SuperAgers are resistant to the normal rate of decline that we see in average elderly, and they're managing to strike a balance between life span and health span, really living well and enjoying their later years of life," says Emily Rogalski, associate professor at the Cognitive Neurology and Alzheimer's Disease Center (CNADC) at Northwestern University Feinberg School of Medicine.
By studying how SuperAgers are unique, the researchers hope to unearth biological factors that might contribute to maintaining memory ability in advanced age.
Therapies to help slow brain aging
Factors have been discovered that speed up brain aging. For example, obesity in midlife may accelerate brain aging by around 10 years, and both sugar and diet varieties of soda are correlated with fast-tracking brain age, having smaller overall brain volume, poorer episodic memory, and a shrunken hippocampus.
A growing body of evidence suggests that people who experience the least declines in cognition and memory all share certain characteristics:
- partaking in regular physical activity
- pursuing intellectually stimulating activities
- staying socially active
- managing stress
- eating healthily
- sleeping well
Recent research highlights a plethora of ways that we can actively take charge of our health and perhaps decrease the rate at which our brains age.
One intervention that crops up time and time again to stave off age-related mental decline is exercise.
A combination of aerobic and resistance exercise of moderate intensity for at least 45 minutes each session and on as many days of the week as possible has been reported to boost brain power in people aged 50 and over significantly.
Likewise, other research by the University of Miami found that individuals over the age of 50 who engaged in little to no exercise experienced a decline in memory and thinking skills comparable to 10 years of aging in 5 years, compared with those who took part in moderate- or high-intensity exercise. Essentially, physical activity slowed brain aging by 10 years.
Dancing has also shown to have an anti-aging effect on the brain of seniors. A study conducted by the German Center for Neurodegenerative Diseases, Magdeburg, Germany found that while regular exercise can reverse the signs of brain aging, the most profound effect was seen in people who danced.
Playing an instrument
Baycrest Health Sciences in Toronto, Canada, revealed why playing a musical instrument may help older adults ward off age-related cognitive declines and retain their listening skills.
Researchers found that learning to play a sound on a musical instrument changes brain waves in such a way that improves an individual's listening and hearing skills. The alteration in brain activity indicates that the brain rewires itself to compensate for disease or injuries that might prevent a person's ability to perform tasks.
"It has been hypothesized that the act of playing music requires many brain systems to work together, such as the hearing, motor and perception systems," said Dr. Bernhard Ross, senior scientist at Baycrest's Rotman Research Institute. "This study was the first time we saw direct changes in the brain after one session, demonstrating that the action of creating music leads to a strong change in brain activity."
A key component of brain health is diet. Recent research has linked omega-3 and omega-6 fatty acids in the blood with healthy brain aging. Another study has also determined that consuming foods included in the Mediterranean or the MIND diet is associated with a lower risk of memory difficulties in older adults.
Research by the University of Illinois, Champaign, IL, discovered that middle-aged people who have higher levels of lutein - a nutrient that is found in green leafy vegetables, such as kale and spinach, and eggs and avocados - had similar neural responses to younger individuals than of people the same age.
"As people get older, they experience typical decline. However, research has shown that this process can start earlier than expected. You can even start to see some differences in the 30s," informs Anne Walk, a postdoctoral scholar and the first author of the study. "We want to understand how diet impacts cognition throughout the lifespan. If lutein can protect against decline, we should encourage people to consume lutein-rich foods at a point in their lives when it has maximum benefit."
The number of American adults over the age of 65 is set to more than double in 40 years, rising from 40.2 million in 2010 to 88.7 million by the year 2050. Due to this aging population, it will become increasingly important to understand the cognitive changes that go hand in hand with aging.
While many questions remain regarding the aging brain, research is making progress in illuminating what happens to our cognitive functions and memory throughout our lifetime, and it is emphasizing ways we can preserve our mental abilities to improve our quality of life as we advance into older adulthood.