The Miracle of Neurogenesis

in Article, News
November 19th, 2014

Neurogenesis occurs in two areas in the human adult: in the dentate gyrus of the hippocampus and in the olfactory system. The hippocampus is vital to learning new information and memory consolidation, thus it makes sense that new neurons need to be born in that region. The olfactory system is needs neurogenesis to process to new information. Majority of neurogenesis actually occurs during prenatal development. In fact humans initially have more neurons that necessary for survival. Apoptosis (programmed cell death) occurs to prune the synapses established during early development.

Many studies have been conducted that investigate ways to increase neurogenesis. Such activities include voluntary physical exercise or being in enriched environments. Experiments with rats have shown that being in an enriched environment where rats are exposed to complex objects, toys, running wheels, etc. spark improvements in performance of tasks measuring levels of learning and memory. For humans, I suppose an enriched environment could be a place involving novel stimuli or

If you think about it, how could neurogenesis be bad? I mean people with neurodegenerative diseases suffer from the consequences of neuronal loss, right? However, according to a study published in May 2014 in Science, exercise could induce amnesia. An article regarding this study states, “Adult mice that exercised on a running wheel after experiencing an event were more likely than their inactive mates to forget the experience.” Thus it appears that the neurogenesis that occurs during exercise may be “wiping out” neurons that encoded previous memories. Furthermore, when neurogenesis was pharmacologically inhibited scientists observed a recall failure in the rats. This article relates this phenomenon to the fact that children cannot form long term memories until they are 3-4 years of age.

Despite controversy about neurogenesis, olfactory ensheathing cells (OECs) have been used to help a paralyzed man walk once again.  An article published in October in BBC News describes how doctors in Poland accomplished this feat. The first step to this process was to extract cells from the patient’s olfactory bulbs (they removed one olfactory bulb and grew the cells in culture). Two weeks later the cells were implanted in the areas surrounding the spinal cord damage the patient had experienced. This action allowed the spinal cord cells to regenerate because the nerve grafts acted “as a bridge to cross the severed cord.” The implications of this type of surgery are pretty amazing – it could work wonders for paralyzed veterans/other individuals and people dealing with dysfunctions relevant to spinal cord damage.

Sources:

Effects of environmental enrichment and voluntary exercise on neurogenesis, learning and memory, and pattern separation: BDNF as a critical variable – ScienceDirect

Exercise Can Erase Memories – The Scientist

Paralyzed Man Walks Again After Cell Transplant – BBC

– Srijesa K.