Final answer:
The brain experiences shrinkage with age, with an approximate loss of 10-15 percent of brain volume from age 20 to 90. This process is variable and can lead to cognitive impairments like memory loss or dementia.
Step-by-step explanation:
The question asked is about how much the brain shrinks from age 20 to 90. This topic falls within the realm of Biology, specifically related to the study of the human body and the process of aging. It's commonly known that as we age, our brains can undergo physical changes, including shrinkage.
Throughout our lifespan, the brain undergoes periods of growth and decline in size. The process begins with rapid brain development early in life during a period of blooming, followed by a process of pruning during which the brain refines its neural connections for efficiency and complexity. Research has shown that by six years of age, the brain reaches nearly 90 percent of its adult size, experiencing significant complex development during adolescence.
In late adulthood, we observe further changes. The brain begins to lose volume and neurons, which might result in cognitive impairments such as memory loss or diseases like dementia and Alzheimer's. Specifically, it has been reported that the brain can lose up to 5 percent of its weight every decade after age 40, with a more rapid decline after 70. Therefore, from age 20 to 90, one might expect an approximate shrinkage of up to 10-15 percent of the brain's volume, though this can vary widely between individuals.