Neuroscientists at Princeton University have found evidence that mind's growth begins to decrease early in adulthood, long before the onset of old age.
The researchers studied the brains of marmoset monkeys, which are found in Central and South America. They found that soon after the monkeys reached adulthood, the rate at which new neural cells form in the hippocampus region of the animals' brains began to decline. This brain region is associated with both learning and memory.
This is the first time that such a decrease in new cell growth, known as neurogenesis, has been observed in a primate, the biological order that also includes apes and humans.
Elizabeth Gould, Professor of Psychology and co-director of the Program in Neuroscience, said that the findings were encouraging for several reasons, including the implication that researchers might one day find ways of stimulating the human brain to generate neural cells more rapidly at any point in life.
"Past theories have suggested that complex brains, like those in monkeys and humans, undergo no changes in brain structure once adulthood is reached," she said.
"These new findings, however, offer further evidence that the primate brain actually shows a remarkable amount of structural reorganization over time. It declines with age, but it does persist at a lower level. Whatever stimulates these changes can most likely be tapped into and enhanced," she added.
Marmosets monkeys reach sexual maturity around the age of 18 months, and commonly begin showing the telltale signs of old a ge like dementia and arthritis at around the age of 8 years.
The researchers examined the neural cell growth in 17 marmosets of both genders, all of which were between 18 months and 7 years of age. They found that the younger adults still showed vigorous new cell growth in the hippocampus.
However, the older the monkey was, the fewer new brain cells had appeared.
"This news isn't entirely negative, though it seems to be at first glance. The silver lining here is that neurogenesis continues long past puberty and does not stop entirely, even in older primates. What's more, it can be stimulated with experience," Gould said.
She believes that some of the ways by which adult neurogenesis can be stimulated in rodents—such as allowing them to socialize and encouraging neural growth through exercise—can work in primates also.
"This means we can be confident that what we discover about the rodent brain can be applied to primates. We'd like to do more studies to see if we can find out first what maintains the higher level of neurogenesis in young animals, and then how we can keep it going at that level as the brain ages," she said.
Gould has cautioned that it is too early to conclude that the new findings will be purely applicable to the human brain. She, however, insists that the study suggests that methods of maintaining the mind's flexibility do exist.