Soon enough, a clear picture emerged: the human hippocampus, a brain area critical to learning and memory and often the first region damaged in Alzheimer’s patients, showed evidence of adult neurogenesis. Gage’s collaborators in Sweden were getting the same results. Wanting to be absolutely positive, Gage even sent slides to other labs to analyze. In November 1998, the group published its findings, which were featured on the cover of Nature Medicine.1
“When it came out, it caught the fancy of the public as well as the scientific community,” Gage says. “It had a big impact, because it really confirmed [neurogenesis occurs] in humans.”
Fifteen years later, in 2013, the field got its second (and only other) documentation of new neurons being born in the adult human hippocampus—and this time learned that neurogenesis may continue for most of one’s life.2 Neuroscientist Jonas Frisén of the Karolinksa Institute in Stockholm and his colleagues took advantage of the aboveground nuclear bomb tests carried out by US, UK, and Soviet forces during the Cold War. Atmospheric levels of 14C have been declining at a known rate since such testing was banned in 1963, and Frisén’s group was able to date the birth of neurons in the brains of deceased patients by measuring the amount of 14C in the cells’ DNA.
“What we found was that there was surprisingly much neurogenesis in adult humans,” Frisén says—a level comparable to that of a middle-aged mouse, the species in which the vast majority of adult neurogenesis research is done. “There is hippocampal neurogenesis throughout life in humans.”
But many details remain unclear. How do newly generated neurons in adults influence brain function? Do disruptions to hippocampal neurogenesis play roles in cognitive dysfunction, mood disorders, or even psychosis? Are there ways to increase levels of neurogenesis in humans, and might doing so be therapeutic? Researchers are now seeking to answer these and other questions, while documenting the extent and function of adult neurogenesis in mammals.
https://archive.is/sVwtG
Researchers have also demonstrated that neurogenesis occurs in the adult human brain, though the locations and degree of cell proliferation appear to differ somewhat from rodents. Strong evidence now exists that new neurons are born in the dentate gyrus of the hippocampus, where they integrate into existing circuits. But so far, there is no definitive support for the migration of new neurons migrating from the subventricular zone (SVZ) of the lateral ventricle to the olfactory bulb, which is atrophied relative to the olfactory bulb of rodents and other mammals that rely more heavily on smell. However, one study did report signs of neurogenesis in an area next to the SVZ, the striatum, which is important for cognitive function and motor control.
https://archive.is/Ti2LU