By Jose Rangel '21

A conflicting new study has emerged from the research labs of University of California, San Francisco, further adding to the debate whether neurons are replenished in adult brains or if humans remain with a defined set after reaching adulthood.

The process of neurogenesis, where progenitor cells (stem cells) create neurons, remains to be a clouded research subject that scientists are unable to firmly agree upon. Previously, few studies have indicated that hundreds of neurons in the adult brain are created every day, but others have documented merely a fraction of what the former studies indicate. Nevertheless, both sides believe in the importance of understanding the physiology and mechanisms of neurogenesis since it can help create ways to replace dead neuronal cells with healthier counterparts.This study attempts to add more data to the debate by observing the subgranular zone, near the dentate gyrus of the hippocampus, an area confirmed to be vital for the formation of memories and the ability to learn. Using a sample size of 59 postoperative and postmortem human tissue samples from the hippocampus, the researchers surprisingly found no newly formed neurons or progenitor cells near the subgranular zone during adulthood.In fact, fewer and fewer progenitor cells and immature neurons were found in samples starting from the 22-week gestational period as opposed to their flourishing numbers at the 11-week period. As each sample size of older subjects was observed, massive diminishments were found to the point where the oldest sample that contained immature neurons was at age 13. Beyond that point, no progenitor or new neuronal cells were seen to be found, contrary to the other few studies performed by other institutions.These observations were considered to be controversial in the scientific community with many scientists like René Hen, a professor of Columbia University’s departments of psychiatry, neuroscience, and pharmacology, expressing their doubts on the “provocative” study. For them, the quality of the samples used could have greatly influenced the outcomes; claiming that postmortem human tissue is usually poor in quality, causing sought for neurons to not be easily found.However, many other scientists believe in the importance of the study, recognizing that the results should not be put to the side until a more concrete explanation could be found. Jason Snyder, an assistant professor in the department of psychology at the University of British Columbia believes there could be profound effects on the study’s results. By further understanding the progenitor cells that affect the hippocampal site, the ability to replace the neurons that have died can be plausible.A great magnitude of importance can result from learning about the current state of neurogenesis in the adult brain. The future for how medical professionals treat mental illness can be substantially improved if progenitor cells are deemed fit to enhance the plasticity and recovery of the mind. Surgeries or even pharmaceutical drugs utilizing progenitor cells could possibly help reverse the negative side effects of mental conditions like Alzheimer’s or Parkinson’s disease by repairing the damaged tissue. Perhaps within the foreseeable future, the old tales of bodily rejuvenation can be turned into a reality, and mental fortitude can be restored to previous intervals of healthier living.