Adult Neurogenesis Claims Are a Case Study of Neuroscientists Dogmatically Asserting Dubious Claims

Do human adult brains create new brain cells or neurons? The neuroscientist belief community cannot get its story straight on this topic. Very many neuroscientists matter-of-factly claim that the brains of human adults do create new neurons, and thereby assert as fact the doctrine of adult neurogenesis. Many other neuroscientists matter-of-factly claim that the brains of human adults do not create new neurons, and thereby deny the doctrine of adult neurogenesis.

Neuroscientists Teaching the Doctrine of Adult Neurogenesis

Let us first look at some neuroscientists who have asserted the doctrine of adult human neurogenesis, by claiming that human adults do create new brain cells. 

• In a 1998 paper "Adult Neurogenesis in the Adult Human Hippocampus, one that has been cited more than 8000 times, scientists claimed "we demonstrate that new neurons, as defined by these markers, are generated from dividing progenitor cells in the dentate gyrus of adult humans," and that "Our results further indicate that the human hippocampus retains its ability to generate neurons throughout life." 
• A 2014 paper claimed, "Our findings demonstrate a unique pattern of neurogenesis in the adult human brain."
• A 2015 paper claimed that "it is now known that neurogenesis persists throughout the human lifespan, and new neurons are being formed in the adult brain."
• A 2021 paper claimed that "most published studies provide evidence for childhood and adult neurogenesis in the human brain stem cell niches."
• A 2022 paper predicted that future studies "will confirm our indications that adult human neurogenesis is orchestrated in a broad brain area."
• A 2018 paper notes that "Renewed discussion about whether or not adult neurogenesis exists in the human hippocampus, and the nature and strength of the supporting evidence, has been reignited by two prominently published reports with opposite conclusions," but nonetheless says "there is currently no reason to abandon the idea that adult-generated neurons make important functional contributions to neural plasticity and cognition across the human lifespan."

Neuroscientists Recently Denying the Doctrine of Adult Neurogenesis

Let us now look at some neuroscientists who have denied the doctrine of adult human neurogenesis, by denying that human adults  create new brain cells. 

• A 2018 paper states, "Our recent observations suggest that newborn neurons in the adult human hippocampus (HP) are absent or very rare (Sorrells et al., 2018)." The paper notes that "studies supporting the presence of adult human hippocampal neurogenesis are not consistent with each other: some report a sharp decline and small, negligible contribution in adults...others support continuous high levels of neurogenesis in old age (Spalding et al., 2013; Boldrini et al., 2018), but show extremely high variability."
• A 2018 paper states "2 independent papers coming from different parts of the world have used a similar approach and methodology leading to converging results and the following similar conclusions: hippocampal neurogenesis in humans decays exponentially during childhood and is absent or negligible in the adult." It says these papers "are Sorrells et al. (2018) from the lab of Alvarez-Buylla in USA published in March in Nature, and the study by Cipriani and coworkers from the Adle-Biassette’s lab in France published in this issue of Cerebral Cortex (2018; 27: 000–000)."
• A 2018 article in The American Scientist (co-authored by Sorrells and Alvarez-Buylla) is entitled "No Evidence for New Adult Neurons."  It said, "Adult human brains don’t grow new neurons in the hippocampus, contrary to the prevailing view." The authors previous reports of adult neurogenesis partially by saying they "frequently used only a single protein to identify new neurons," which was a faulty technique because "we found that the protein most often used, one called doublecortin, can also be seen in nonneuronal brain cells (called glia) that are known to regenerate throughout life." A 2022 article entitled "Doublecortin and the death of a dogma" refers to work by Franjic, saying, "out of the 139,187 nuclei sequenced, only 2 showed appropriate transcriptomes for neural precursor cells... suggesting adult human neurogenesis is rare, if it occurs at all."
• A 2019 paper says that "a balanced review of the literature and evaluation of the data indicate that adult neurogenesis in human brain is improbable," and that "several high quality recent studies in adult human brain, unlike in adult brains of other species, neurogenesis was not detectable."
• A 2018 paper claimed that "New neurons continue to be generated in the subgranular zone of the dentate gyrus of the adult mammalian hippocampus," but the paper's title was "Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults."
• Describing his research, the neuroscientist  Ashutosh Kumar stated in 2020 that he had found this: "Progression of neurogenesis is restricted after childhood, and reduces to negligible levels around adolescence and onwards."
• A 2022 paper was entitled "Mounting evidence suggests human adult neurogenesis is unlikely."
• A 2022 paper states, "In this review, we will assess critically the claim of significant adult neurogenesis in humans and show how current evidence strongly indicates that humans lack this trait." The paper states that "In summary, a thorough review of the literature shows that there is no scientific convincing evidence of the generation and incorporation of new neurons into the circuitry of the adult human brain, including the dentate gyrus of the hippocampus."  Noting how false claims persist within neuroscience, the paper states, "As Victor Hamburger, co-discoverer of the nerve growth factor, said at an informal meeting: 'A single report of an incorrect finding that many people like, takes more than hundreds of papers with negative findings to make an acceptable correction.' ” 
• A 2021 paper was entitled "Positive Controls in Adults and Children Support That Very Few, If Any, New Neurons Are Born in the Adult Human Hippocampus."

What the examples here mainly show is an example of the tendency of many neuroscientists to state as if they were facts extremely dubious claims. That goes on all over the place in the world of neuroscience. It occurs most commonly when neuroscientists make extremely dubious and unproven claims that memories are stored in the human brain, and that the human brain is the cause of human thinking, self-hood and imagination.