There is increasing evidence that adult humans continue to grow new neurons in their brains [1], even up to the age of 100 years [2] and presumably beyond. Neurogenesis, or growth of new neurons, has been studied in adult rats and other mammals [e.g., 3]. Evidence of adult neurogenesis overturned the prevailing belief that the adult brain was fixed and incapable of regeneration. As these findings become more popularized, what will this mean for our concepts of aging?
It was long believed that brain development was completed around the age of 6 years old. This had disastrous consequences for people born with phenylketonuria (PKU) an inborn error of metabolism in which people cannot break down the amino acid phenylalanine. Phenylalanine is a neurotoxin that readily crosses the blood-brain barrier. What is remarkable is that PKU can be completely controlled by a very restrictive diet limited in phenylalinine. Children with PKU who are untreated will have significant cognitive deficits and have to be institutionalized as adults. Since the 1960s every baby in North America has been tested at birth for PKU.
Until the 1980s the standard recommendation was to discontinue treatment of children with PKU after the age of 6 years old. Subsequently researchers found a severe decline in intellectual function in children who had gone off diet [4]. The current recommendation for people with PKU is that they stay on diet their entire lives.
Assumptions regarding the age at which the brain is “complete” has had consequences for people living with PKU. As the evidence of neurogenesis in adult humans emerges, how will that affect the way we think about age? Continue reading
Neuroethics at the Core 