Neurogenesis occurs during embryonic development, and also in parts of the adult brain following birth.
This process, known as adult neurogenesis, was first recognised in the 1960s, although it took until the 1990s for the field as a whole to accept that neurogenesis in adult animals could play a substantial role in brain function. Integral to this realisation was the discovery in 1992 by Professors Perry Bartlett and Linda Richards that the adult mouse brain contains neural stem cells. Because stem cells can divide, and differentiate into many types of cells, their discovery in adult brains suggested that neurogenesis could hold the key to treating neurodegenerative conditions such as Alzheimer’s disease. Since then, neurogenesis has also been found to occur in the hippocampi of adult humans.
Adult neurogenesis is known to occur in two regions in the mammalian brain:
- the subgranular zone (SGZ) of the dentate gyrus in the hippocampus, which is a region that is involved in regulating learning and memory
- and the subventricular zone (SVZ), which is situated throughout the lateral walls of the brain’s lateral ventricles (see figure below).
What is the function of adult neurogenesis?
Neurons formed in the SVZ migrate to the olfactory bulb, which is the area of the brain responsible for olfaction, our sense of smell. Preventing adult neurogenesis in the SVZ has been shown to impair cognitive functions including olfactory memory.
Newborn neurons resulting from adult neurogenesis in the hippocampus play crucial roles in regulating mood, memory and spatial learning. In 2015, neuroscientists discovered two distinct types of stem cells in the hippocampus, suggesting that different areas in the hippocampus are responsible for controlling spatial learning and mood.
Can adult neurogenesis be increased?
Research on the dentate gyrus of the hippocampus suggests that different factors can modulate adult neurogenesis. QBI researchers, for example, have found that exercise increases neurogenesis in the dentate gyrus, resulting in the increased production of newborn neurons.
Conversely, depression has been found to decrease neurogenesis, and adult neurogenesis has also been shown to decline with age.
Neuroscientists are now interested in developing ways to harness the brain’s reservoir of neural stem cells and progenitor cells to enhance hippocampal neurogenesis. By increasing production of newborn neurons, neuroscientists may be able to treat age-associated cognitive decline, neurodegenerative diseases including dementias, and mental illnesses.