As adults, some parts of our brains form new cells in a process known as neurogenesis, while others do not. There are also many parts of the brain that remain unexplored in this regard. Now the amygdala, the part of the brain that controls fear and emotional memories, has been added to the list of places where adult neurogenesis occurs. Hopefully, the discovery will lead to better treatments for post-traumatic stress disorder (PTSD) and crippling phobias.
Adult neurogenesis has been a contentious topic for a long time. Scientists who claimed to have found evidence of it were once ridiculed, but stem cells that form new cells even as we age have now been confirmed in the hippocampus – the part of the brain responsible for much of our memory processing. Professor Perry Bartlett of the Queensland Brain Institute, who led the hippocampus discovery, has co-authored a paper in Molecular Psychiatry showing that something similar takes place in the amygdala.
First author Dr Dhanisha Jhaveri told IFLScience that several techniques were used to confirm adult neurogenesis in the amygdala of mice. “We looked for the presence of stem cells, which we did indeed find, although in small numbers. We also have techniques to find analogues that only get incorporated into dividing cells."
These not only revealed the presence of new cells, but demonstrated their conversion to functional neurons. Jhaveri also injected mice with a retrovirus that only infects cells in the process of dividing to form new cells. She found that six to eight weeks later parts of the mouse amygdala were infected.
Although this research hasn't been done in humans, Jhaveri pointed out that when other areas of the mouse brain were shown to support adult neurogenesis, the result was then seen in humans too.
Presumably, there are evolutionary reasons why some parts of the brain can support adult neurogenesis and others can’t, but Jhaveri said these remain a mystery. She did note, however, that there are strong connections between the hippocampus and amygdala, with both playing a role in emotional learning and processing on a daily basis. Consequently, it's not surprising that the two regions share this feature. Yet even within the amygdala, only some sections were found to support stem cells.
The team showed that the amygdala stem cells could be stimulated to proliferate. Jhaveri speculates that the production of new cells in those regions that inhibit, rather than promote, fear responses could damp down the amygdala overactivity that is a known feature of PTSD. However, she acknowledges the process required could also turn out to be much more complex.
“We’ve opened the door to completely unchartered territory,” Jhaveri told IFLScience. “It’s only going to get more exciting from now on.”