Neurogenesis is the process by which new neurons are formed in the brain. Neurogenesis is crucial when an embryo is developing, but also continues in certain brain regions after birth and throughout our lifespan. Neurogenesis, or the birth of new neuronal cells, was thought to occur only in developing organisms. ... Examples of neurogenesis are found in the hippocampus of mammals, song control nuclei of birds and the olfactory pathway of rodents, insects and crustaceans.

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. In contrast, neurogenesis in humans generally begins around gestational week (GW) 10 and ends around GW 25 with birth about GW 38-40.

Neurogenesis in mammals:
During embryonic development, the mammalian central nervous system (CNS; brain and spinal cord) is derived from the neural tube, which contains NSCs that will later generate neurons. However, neurogenesis doesn't begin until a sufficient population of NSCs has been achieved. These early stem cells are called neuroepithelial cells (NEC)s, but soon take on a highly elongated radial morphology and are then known as radial glial cells (RGC)s. RGCs are the primary stem cells of the mammalian CNS, and reside in the embryonic ventricular zone, which lies adjacent to the central fluid-filled cavity of the neural tube.

Adult neurogenesis:
Neurogenesis can be a complex process in some mammals. In rodents for example, neurons in the central nervous system arise from three types of neural stem and progenitor cells: neuroepithelial cells, radial glial cells and basal progenitors, which go through three main divisions: symmetric proliferative division; asymmetric neurogenic division; and symmetric neurogenic division. Out of all the three cell types, neuroepithelial cells that pass through neurogenic divisions have a much more extended cell cycle than those that go through proliferative divisions, such as the radial glial cells and basal progenitors.

Another factor is central nervous system injury since neurogenesis occurs after cerebral ischemia, epileptic seizures, and bacterial meningitis. On the other hand, conditions such as chronic stress, viral infection. and aging can result in a decreased neuronal proliferation.

Aerobic activities such as running, cycling, swimming, and even sex, are effective ways of boosting neurogenesis. The aim is getting the heart pumping for more than 20 minutes at a time, and on a regular basis. In this state levels of several growth hormones are elevated in the brain. Intake of flavonoids, which are contained in dark chocolate or blueberries, will increase neurogenesis. Omega-3 fatty acids, present in fatty fish, like salmon, will increase the production of these new neurons. Conversely, a diet rich in high saturated fat will have a negative impact on neurogenesis. Caffeine affects behaviors and biochemical pathways that have been shown to influence the rate of neurogenesis in the adult hippocampus. At moderate doses, caffeine increases locomotor activity (Fredholm et al., 1999), which has been shown to increase neurogenesis in the dentate gyrus (van Praag et al., 1999).

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